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Lateral variability in predation and taphonomic characteristics of turritelline gastropod assemblages from Middle Eocene - Lower Oligocene strata of the Gulf Coastal Plain, United States
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Lateral variability in predation and taphonomic characteristics of turritelline gastropod assemblages from Middle Eocene - Lower Oligocene strata of the Gulf Coastal Plain, United States
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LATERAL VARIABILITY IN PREDATION AND TAPHONOMIC CHARACTERISTICS O F TURRITELLINE GASTROPOD ASSEMBLAGES FROM MIDDLE EOCENE-LOWER OLIGOCENE STRATA O F THE GULF COASTAL PLAIN, UNITED STATES by J a m e s Whitey Hag adorn A T h esis P resented to th e FACULTY O F THE GRADUATE SCHOOL UNIVERSITY O F SOUTHERN CALIFORNIA In Partial Fulfillment of th e R equirem ents for th e D egree MASTER O F SCIENCE (Earth S ciences) May 1995 Copyright 1995 Ja m e s Whitey H agadorn UNIVERSITY OF SOUTHERN CALIFORNIA THE GRADUATE SCHOOL UNIVERSITY PARK LOS ANGELES. CALIFORNIA S 0 0 0 7 This thesis, written by ....^ ^ s.J ^ ite y „ H a sa d o r n ............................................... under the direction of h i s Thesis Committee, and approved by all its members, has been pre sented to and accepted by the Dean of The Graduate School, in partial fulfillment of the requirements for the degree of Master of Science Dr an IOMMITTEE Chairman ACKNOWLEDGMENTS I am deeply indebted to the many people who have assisted m e with this project. Those who I wish to thank follow, in no particular order. My advisor, Dave Bottjer, for encouragem ent, support, advice, funky food, and sticky-notes. Al and Gors, for asking the right questions and giving advice along the way. Many other dept, profs for answering my questions after repeatedly barging into their office. The incredible paleolabbers, past and present, for encouragem ent, discussion, support, and advice for this project and for the nuances of grad school in general. To the many fellow gradstus who have helped m e along the way (either a s buds or as scientific advisors and compatriots) - you know who you are. Deborah Fischer for putting up with all of my crap whilst in grad school ~ without her ability to drag m e away from my computer, I might have ended up wearing a pocket protector. Ozzy for allowing me to m ake a m ess in his basem ent lab whilst processing sam ples and Dave Foley for lending m e his magnifying coat-rack to examine specim ens. Warren Allmon, Patricia Kelley, Thor Hansen, Dan Miller, David Dockery, Emily Vokes, LouElla Saul, and Laurie Anderson provided much help and advice along the way and led me to the localities and subject matter of this M.S. thesis. I thank the many institutions which let me use their collections, including the Los Angeles County Museum of Natural History, the Alabama Geological Survey, the Mississippi Geological Survey, Tulane University, and Louisiana State University. The many folks at th ese institutions gave m e invaluable help by making the time to help m e locate specim ens, locality information, and most importantly, provided me access to and loan of specim ens for extended periods of time. This project w as supported by g ran ts from th e U.S.C. Dept, of Earth S cien ces G rad u ate S tudent R esearch Fund, Sigm a Xi, and th e Paleontological Society. iv TABLE OF CONTENTS LIST O F FIGURES viii LIST O F TABLES ix ABSTRACT 1 INTRODUCTION 3 GEOLOGIC SETTING 16 S to n e City B eds 17 Lisbon Form ation 23 G osport S an d 26 M oodys Branch Form ation 29 Byram Form ation 3 2 M ETHODS 3 8 Field Sam pling S trategy 3 8 Laboratory P rocessing & D ata Collection S trategy 4 0 M useum C ollections 46 D ata A nalysis & P resentation 4 6 Mixed S p e c ie s 4 7 Within S p e c ie s 4 8 Statistical A pproaches 4 9 R ESU LTS 51 Sam pling Reproducibility 52 P redator and Prey Size C haracteristics 53 B etw een S p ecies: Within S am p les 53 S to n e City B eds 53 M oodys Branch Form ation 58 Lisbon Form ation 60 G osport S and 61 S um m ary 62 Mixed S p ecies: B etw een S am p les 62 S um m ary 64 Mixed S p ecies: B etw een O utcrops 67 S um m ary 67 Mixed S pecies: B etw een Form ations 70 S um m ary 70 Within S pecies: B etw een S am p les 73 Mesalia claibornensis 73 Mesalia vetusta 74 Turritella apita 74 Turritella alveata 75 Turritella carinata 76 Turritella fischeri 77 Turritella ghigna 78 Turritella mississippiensis 78 Turritella nasuta 79 Turritella obruta 79 Turritella perdita 80 S um m ary V 81 Within S pecies: Betw een O utcrops 83 S um m ary 86 Within S pecies: Betw een Form ations 86 S um m ary 89 Predation C haracteristics 89 B etw een S pecies: Within S am p les 89 S tone City B eds 89 M oodys Branch Form ation 93 Lisbon Form ation 95 G osport S an d 95 S um m ary 96 Mixed S pecies: B etw een S am p les 97 S um m ary 99 Mixed S p ecies: B etw een O utcrops 99 S um m ary 100 Mixed S pecies: B etw een Form ations 100 S um m ary 101 Within S p ecies: B etw een S am p les 101 Mesalia Claibornensis 101 Mesalia vetusta 102 Turritella apita 103 Turritella alveata 103 Turritella carinata 105 Turritella fischeri 106 Turritella ghigna 106 Turritella mississippiensis 107 Turritella nasuta 107 Turritella obruta 108 Turritella perdita 108 S um m ary 110 Within S pecies: Betw een O utcrops 110 S um m ary 112 Within S pecies: Betw een Form ations 112 S um m ary 113 T aphonom ic C haracteristics 114 B etw een S pecies: Within S am p les 114 S to n e City B eds 114 M oodys Branch Form ation 114 Lisbon Form ation 116 G osport S and 116 S um m ary 117 Mixed S pecies: B etw een S am p les 117 S um m ary 118 Mixed S pecies: B etw een O utcrops 118 S um m ary 119 Mixed S pecies: Betw een Form ations 119 vi Sum m ary 120 Within S pecies: Between S am ples 120 Mesalia claibornensis 120 Mesalia vetusta 121 Turritella apita 121 Turritella alveata 122 Turritella carinata 123 Turritella fischeri 124 Turritella ghigna 124 Turritella mississippiensis 124 Turritella nasuta 125 Turritella obruta 125 Turritella perdita 126 Sum m ary 127 Within Species: Between O utcrops 127 Sum m ary 128 Within Species: Between Form ations 128 Sum m ary 130 M useum Collections 130 Betw een S p ecies Variability 130 Lisbon Formation 130 G osport Sand 133 S tone City B eds 134 Moodys Branch Formation 135 Sum m ary 135 Studied O utcrops vs. Museum Collections: Mixed S p ecies M eans 137 Lisbon Formation 137 G osport Sand 139 S tone City B eds 139 Moodys Branch Formation 140 Sum m ary 141 Studied O utcrops vs. M useum Collections: Within S p ecies M eans 141 Mesalia claibornensis, Lisbon Formation 143 Mesalia claibornensis, Stone City B eds 143 Mesalia vetusta, Gosport Sand 145 Turritella apita, G osport Sand 146 Turritella alveata, Moodys Branch Formation 147 Turritella carinata, G osport Sand 148 Turritella carinata, Lisbon Formation 148 Turritella ghigna, G osport Sand 149 Turritella mississippiensis, Byram Formation 150 Turritella nasuta, S tone City B eds 151 Turritella obruta, Gosport Sand 152 Turritella perdita, Moodys Branch Formation 152 Sum m ary 153 vii DISCUSSION 155 W ithin-Sam ple Variability 155 B etw een-S am ple Variability 159 Mixed S p e c ie s 160 Within S p e c ie s 160 B etw een-O utcrop Variability 164 Mixed S p e c ie s 164 Within S p e c ie s 164 B etw een-Form ation Variability 165 Mixed S p e c ie s 165 Within S p e c ie s 165 Variability in Different M odes of D ata S ynthesis and in Different P aram eters 166 B etw een S am p les 166 Betw een O utcrops 169 Betw een Form ations 170 Drilling Predation: T ernary D iagram s 170 M useum Collections 181 W ithin-Formation Variability 181 M useum - vs. O utcrop-B ased R esults 182 C om parison of Mixed S p ecies R esults 182 C om parison of Within S p ecies R esults 183 Variability in Different M odes of D ata S ynthesis and in Different P a ram eters 184 Study Variability and Published R esults 185 Prey S ize P aram eters 186 Predation P aram eters 188 Drilling Intensity 189 Drilling Efficiency 190 Peeling Intensity 192 Sum m ary and D iscussion 193 CO N CLU SIO N S 199 REFEREN CES 202 LIST OF FIGURES Figure 1: Photos of turritelline gastropods. 9 Figure 2: G eneralized locality m ap. 18 Figure 3: Stratigraphic section of Tertiary units of the Gulf C oast. 19 Figure 4: G eneralized stratigraphic section for th e S tone City Beds. 21 Figure 5: Locality m ap for th e Stone City B eds locality. 22 Figure 6: G eneralized stratigraphic section for the Lisbon Formation. 24 Figure 7: Locality m ap for th e Lisbon Formation locality. 25 Figure 8: G eneralized stratigraphic section for the G osport Sand. 27 Figure 9: Locality m ap for th e G osport Sand locality. 28 Figure 10: G eneralized stratigraphic section for the Moodys Branch Formation. 30 Figure 11: Locality m ap for th e Moodys Branch Formation. 31 Figure 12: Locality m ap for th e Moodys Branch Formation locality. 33 Figure 13: Locality m ap for th e Moodys Branch Formation locality. 34 Figure 14: G eneralized stratigraphic section for th e Byram Formation. 36 Figure 15: Locality m ap for th e Byram Formation locality. 37 Figure 16: P aram eters m easured in this study. 42 Figure 17: Whorl profiles of all turritelline gastropods utilized in this study. 54 Figure 18: Ternary plot of E ocene taxa m eans. 173 Figure 19: T ernary plot of E ocene sam ple m eans. 175 Figure 20: T ernary plot of Oligocene sam ple and outcrop m eans. 176 Figure 21: T ernary plot of all outcrop m eans. 177 Figure 22: T ernary plot of all formation m eans. 178 Figure 23: T ernary plot of epoch m eans. 179 Figure 24: C om posite ternary diagram of E ocene and Oligocene results. 180 ix 55 63 65 66 68 69 71 72 82 84 85 88 91 98 131 132 136 138 142 144 154 187 LIST OF TABLES Predator and prey size characteristics for all studied taxa. P-values for com parisons of taxa within sam ples. M ixed-species predator and prey size characteristics. M ixed-species p-values for within-outcrop com parisons. Mixed sp ecies values for all studied param eters. M ixed-species p-values for within-formation com parisons. M ixed-species values for all studied param eters. M ixed-species p-values for betw een-form ation com parisons. W ithin-species p-values for within-outcrop com parisons. W ithin-species values for all studied param eters. W ithin-species p-values for within-formation com parisons. W ithin-species values for all studied param eters. W ithin-species p-values for betw een-form ation com parisons. W ithin-species predation and taphonom ic characteristics. M ixed-species predation and taphonom ic characteristics. Sum m ary information for m useum collection data. M ean values and sam ples sizes for m useum specim ens. P-values for betw een-species m useum com parisons. M ixed-species values of m useum and outcrop specim ens. M ixed-species p-values for m useum -to-outcrop com parisons. W ithin-species m ean s and sam ple sizes for formations. P-values for w ithin-species m useum -to-outcrop com parisons. V alues utilized from literature reports. ABSTRACT Lateral variability in predation and taphonomic characteristics of turritelline gastropod assem blages was examined in Middle Eocene to Lower Oligocene strata from the Gulf Coast of the United States. Multiple bulk sam ples were taken from horizons of fossiliferous shell-beds which are commonly sam pled in large-scale studies of predation. T hese sam ples were utilized to determine if lateral variability is a common feature of these deposits, and if so, how it may affect large-scale studies of predator-prey interactions. W idespread variability (in a suite of paleobiologic and taphonomic characters) w as encountered between taxa in a given sample, between sam ples of the sam e outcrop, between outcrops of the sam e formation, and between formations of similar age. Probabilities of identifying the sources of variability at these different scales are higher when variability is examined within the sam e taxon, rather than between mixed-taxa results. In addition, probabilities of identifying sources of variability are highest when examining the principal abundant taxa from well-sampled outcrops. Among the studied param eters, variability in specim en size is most common at all scales. Variability in taphonomic characteristics of sam pled shells is also common. Variability in predatory characteristics, such as shell drilling and peeling, is not common. These preliminary results indicate that there is a strong possibility of encountering "Type I" sampling errors when collecting sam ples from outcrops which exhibit high levels of lateral variability. In this context, a Type I sampling error would occur if an erroneous conclusion w as reached based on erroneous, or in this case, non-representative sam ples collected from an outcrop. Similar variability within m useum -based collections w as also observed. 2 Comparison of field-based to m useum -based results (for similar taxa from the sam e outcrops) indicates strong biases may affect the latter. Although museum collections are characterized by bias, in general it appears that this bias may not affect large-scale studies of predation intensity and efficiency. Similar com parisons of field- to literature-based results indicate that there are pervasive differences between published results and study results for taxa which are collected from the sam e outcrop and analyzed for the sam e param eters. These results suggest that large-scale studies of predation need to test for, and constrain the incidence of outcrop-scale variability in order to m ake certain that collected sam ples actually "represent" the studied outcrops or horizons from whence they cam e. Records from all studied strata exhibit high variability in most of the studied characteristics, so much so that the sampling of a few dozen shells from a given locality or museum collection is not likely to give an accurate picture of the paleobiologic or taphonomic characteristics of the taxa under study. In order to constrain outcrop-based data sources, large- scale predation studies may need to revise sampling strategies to include usage of multiple bulk sam ples and/or collection of multiple sam ples along lateral transects of studied horizons. IN TR O D U C TIO N M olluscan-rich strata from the Gulf and Atlantic coastal plains have been u sed in a variety of long-term, large-scale paleobiologic and paleoecologic studies which have focused on predator-prey interactions (e.g., Carriker and Y ochelson, 1968; T hom as, 1976; Vermeij, 1977; 1987; Dudley and Vermeij, 1978; Kelley, 1988, 1989, 1992; Allmon et al., 1990; A nderson, 1992; Kelley and H ansen, 1993; H ansen and Kelley, in press). In particular, m any of th e se stu d ies (e.g., A degoke and T evesz, 1974; Dudley and Vermeij, 1978; Vermeij et al., 1980; Kitchell et al., 1981; Vermeij, 1982, 1983, 1987; Taylor et al., 1983; K abat and Kohn, 1986; Kitchell et al., 1986; Kelley, 1988, 1989, 1992; Allmon et al., 1990; A nderson, 1992; Kelley and H ansen, 1993; Tull and B ohning-G aese, 1993; H ansen and Kelley, in press) have focused on evolution and escalation of predator and prey taxa in the context of biotic interactions (e.g., Sohl, 1969; Van Valen, 1973), m ore comm only known a s the M esozoic M arine Revolution of Vermeij (1977). T he M esozoic Marine Revolution is thought to be o n e of the critical evolutionary trends of th e post-Paleozoic b e c a u se interactions (and h en ce competition, predation, defense, etc.) betw een invertebrate predator and prey organism s are thought to have intensified, or escalated [e.g., Vermeij, 1977, 1987; but also s e e original ideas e x p ressed in Sohl (1969) and in a m ore general se n se , Van Valen (1973)]. For exam ple, com parisons of intensities of shell-peeling and shell-drilling am ong bivalves and g astro p o d s indicate a nearly four-fold increase in intensity from the M esozoic to the C enozoic (e.g., Dudley and Vermeij, 1978; Vermeij et al., 1980; Vermeij, 1987; Allmon et al., 1990). C oncom itant with this escalation of predation, th ere w as an increase in shell-sturdiness (e.g., changing shell architecture) am ong g astropods (Vermeij, 4 1977, 1987; Kelley, 1989). Prior to the C retaceous, levels of predator-prey interactions am ong th e s e taxa a re thought to have been low (Sohl, 1969; Vermeij, 1977, 1987; Dudley and Vermeij, 1978; Vermeij et al., 1980; Allmon et al., 1990; Kelley and H ansen 1993). In addition, a b u n d an c es and diversity of shell-drilling g astropods w ere low [e.g., Sohl, 1969; but also s e e Allmon (1992b) for discussion of m acroevolutionary patterns in the light of varying generic definitions]. N ear the end of the M esozoic, however, both the intensity of shell-drilling predation and th e occurrence of drilled prey shells, including g astro p o d s and bivalves, increased greatly (Sohl, 1969; Vermeij, 1977, 1987; Dudley and Vermeij, 1978; Vermeij et al., 1980; Allmon et al., 1990; Kelley and H ansen 1993). In resp o n se to increased num bers of predators and increased intensity of predation, it h a s b een hypothesized that prey taxa evolved behavioral and/or structural adaptations for d efen se or avoidance of predators (Vermeij, 1977, 1987). As a result of increasing interest in predator-prey biotic interactions, m any large-scale, long-term studies have been undertaken which have focused on testing and refining th e hypothesis of escalation a s well a s to gain a better understanding of predator-prey interactions (e.g., A degoke and T evesz, 1974; Taylor and Taylor, 1977; Vermeij, 1977, 1982, 1987; Dudley and Vermeij, 1978; Vermeij and Currey, 1980; Vermeij et al., 1980, 1989; Kitchell et al., 1981; Croll, 1983; Taylor et al., 1983; Boggs et al., 1984; DeAngelis et al., 1985; K abat and Kohn, 1986; Kitchell, 1986; Kitchell et al., 1986; Allmon, 1988a, 1992a; Kelley, 1988, 1989, 1992; W alker, 1988; Allmon et al., 1990; A nderson, 1992; W alker, 1992a; Kelley and H ansen, 1993; Tull and B ohning-G aese, 1993; Lieberm an et al., 1993; H ansen and Kelley, in press). Many of th e se studies focus on a single 5 clade, time period, region, or on m odels or exam ination of living fauna in an attem pt to refine basic assum ptions about predator-prey interactions in the fossil record. Although there are m any types of predator-prey interactions which can be studied from the fossil record, including evidence of sponge, algal, fish, and other ty p es of shell-crushing or shell-breaking predation, [see sum m ary in Vermeij (1987)], Vermeij (1977) originally em phasized interactions betw een predatory g astropods and their gastropod prey. Thus, m any su b seq u e n t predation studies, including this one, have followed suit and focused on interactions betw een predatory gastropods and their gastropod or bivalve prey (e.g., Dudley and Vermeij, 1978; Vermeij and Currey, 1980; Vermeij et al., 1980, 1989; Kitchell et al., 1981; Vermeij, 1982; Croll, 1983; Taylor et al., 1983; Boggs et al., 1984; DeAngelis et al., 1985; K abat and Kohn, 1986; Kitchell, 1986; Kitchell et al., 1986; Kelley, 1988, 1989, 1992; Allmon et al., 1990; A nderson, 1992; Kelley and H ansen, 1993; Tull and B ohning-G aese, 1993; H ansen and Kelley, in press). To better understand changing predator-prey interactions, tem poral p attern s of m olluscan predator-prey interactions have been outlined for m uch of th e C enozoic and C retaceous (e.g., A degoke and T evesz, 1974; Vermeij, 1977, 1987; Dudley and Vermeij, 1978; Vermeij et al., 1980; Vermeij, 1982; Taylor et al., 1983; K abat and Kohn, 1986; Kelley, 1988, 1989; Allmon et al., 1990; A nderson, 1992; Kelley and H ansen, 1993; Tull and B ohning-G aese, 1993; H ansen and Kelley, in press). In order to m ake th e se long-term a sse ss m e n ts of predator-prey interactions, it h as been n ecessary to synthesize information from a variety of sources, including data from a variety of taxa, outcrops, m useum s, literature reports, and R ecent a ssem b lag es (see above references). For the 6 m ost part, however, m any large-scale predation studies collect information about predator-prey interactions from field studies of fossiiiferous outcrops (e.g., A degoke and Tevesz, 1974; Taylor et al., 1983; Kabat and Kohn, 1986; Kelley, 1988, 1989, 1992; Anderson, 1992; Kelley and H ansen, 1993; Tull and B ohning-G aese, 1993; H ansen and Kelley, in press). O ther studies com bine results from field studies with information from other similar studies and/or with information from the literature or m useum collections (e.g., Carriker and Yochelson, 1968; Sohl, 1969; Dudley and Vermeij, 1978; Vermeij et al., 1980; Vermeij, 1977, 1982, 1983, 1987; Allmon et al., 1990). R egardless, alm ost all of th ese long-term, large-scale studies of predation have, either directly or indirectly, collected information from molluscan-rich outcrops of C retaceous and Tertiary strata. In order to collect information about predators, including predatory gastropods such a s naticids or muricids, or less commonly, predatory calappid crabs, m any of the aforem entioned large-scale predation studies have utilized a variety of sam pling strategies. T h ese include sam pling collection m ethodologies which: i) often collect only one or two bulk sam ples from a given outcrop; ii) collect information from only one outcrop or horizon of th e studied formation, interval, etc. (e.g., Kabat and Kohn, 1986?); iii) collect sam ples from a variety of outcrops or exposures of the studied interval(s) (e.g., Kelley, 1988, 1989, 1992; H ansen and Kelley, in press); iv) do not indicate collection of bulk sam ples and thus may have collected 'float' or best-preserved surficial sam ples (e.g., Sohl, 1969; Adegoke and T evesz, 1974); v) collect sam ples from m useum collections which m ay have been collected a s bulk sam ples, a s float, a s a combination of the two, or m ay have been preferentially 7 sorted/biased/w innow ed a s a result of m useum usage, curation, sam ple- exchange, etc. (e.g., Taylor et al., 1983); vi) synthesize information from literature reports (e.g., Vermeij, 1982); and vii) utilize a combination of th e se ap p ro ach es (e.g., Carriker and Yochelson, 1968; Sohl, 1969; Dudley and Vermeij, 1978; Vermeij et al., 1980; Vermeij, 1977, 1987; Allmon et al., 1990; A nderson, 1992; Kelley and H ansen, 1993). As a result of th ese sam ple collection strategies, aforem entioned large- scale studies of predation have had to m ake assum ptions about collected sam ples and information in order to outline large-scale and long-term patterns. W hereas the general patterns outlined in th ese studies, such a s the concept of the M esozoic Marine Revolution (Vermeij, 1977), will likely continue to hold true, m any of the nuances of large-scale studies of predation will continue to undergo refinement. With this refinement in mind, this study se e k s to test som e of th e assum ptions m ade by th ese large-scale, long-term studies in utilizing simplified sam pling strategies. In particular, I hypothesize that the aforem entioned predation studies may underestim ate the role sm all-scale heterogeneity m ay play in simplified sam pling strategies which are used to a s s e s s patterns of predator-prey interactions. Sm all-scale heterogeneity, or variability, may m anifest itself at a variety of sc a le s and n eed s to be a sse sse d , or at least considered, w hen devising sam pling strategies to study predator-prey interactions b ased on highly fossiiiferous, often condensed to sem i-condensed shell-beds of the Gulf and Atlantic C oastal Plain. Potential variability m ay exist in three dim ensions within any strata and be visible at a variety of sc ales ranging from within a sam ple to within a formation or epoch (e.g., Schindel, 1980, 1982; Koch and Sohl, 1983; 8 Miller, 1988, 1989). Variability may span paieoenvironmental, taphonomic, temporal, community, lithologic, or other gradients (e.g., Stanton and Evans, 1972; Schindel, 1980, 1982; Koch and Sohl, 1983; Koch, 1987). In order to help a s s e s s effects of sm all-scale variability on large-scale predation studies, this pilot study w as conducted. This pilot study attem pts to a s s e s s one of these potential sources of heterogeneic bias by examining lateral variability at a variety of scales ranging from within-sample to within-epoch. To a s s e s s lateral variability at th ese scales, this pilot study utilizes a suite of param eters which are commonly noted in predation studies (see M ethods section for a more detailed discussion of th ese param eters, including citations) and focuses on one clade of commonly-occurring prey gastropods, the Turritellidae (Fig. 1). The nuances of this study are described in more detail below and in the M ethods section. Most large-scale studies of predation utilize sampling strategies which em phasize vertical sampling within a given interval (e.g., Dudley and Vermeij; 1978; Vermeij et al., 1980; Kelley, 1988, 1989, 1992; Allmon et al., 1990; Kelley and Hansen, 1993; Tull and Bohning-Gaese, 1993, Hansen and Kelley, in press). Commonly, many sam ples are collected at different horizons within a given unit or epoch, w hereas only one or two are collected from each horizon [e.g., Kelley, 1988, 1989, 1992; Allmon et al., 1990; se e also Schindel (1980, 1982), and Koch (1987, 1988)]. In som e instances, bulk sam ples are collected, w hereas in others, bulk sampling is not indicated, leaving the possibility that float has been collected -- oftentimes from a well-weathered horizon (e.g., Adegoke and Tevesz, 1974; Dudley and Vermeij, 1978; Schindel, 1980; Vermeij et al., 1980; Kabat and Kohn, 1986). Descriptions of the lateral extent 9 Figure 1: Photographs of turritelline gastropods similar to those used in this study. T. aflicostata from the Pliocene Yorktown Formation is shown. Note the presence of a complete naticid drillhole in A), multiple naticid drillholes in B), and an incomplete naticid drillhole in C). 10 of outcrop-scale sam ples are rarely provided, illustrating the point that m ost sam pling descriptions in predation studies are 'vertically-biased1 . In addition, descriptions of sam pling efforts rarely indicate how m any sam ples w ere collected at each horizon; w hether they w ere bulk sam ples or float; how large they w ere; how far apart multiple sam ples w ere spaced; or give the range of lateral variation of th e se sam ples relative to the vertical/temporal variation. This dearth of information regarding lateral spacing of sam ples m ay b e a function of abbreviated m ethodologies required by journals, but m ay also result from failure of large-scale predation studies to a s s e s s the reproducibility of the sam pling effort itself. For exam ple, m any of the aforem entioned large-scale predation studies do not ad d ress the possibility that the sam ples they collect m ay not represent the horizon/outcrop/layer from w hence they cam e (also known a s a Type I error; Davis, 1973; Alder and R oessler, 1977). In this context, a Type I sam pling error would occur if an erroneous conclusion w as reached b ased on erroneous or non-representative sam ples collected from an outcrop. For exam ple, if one reached the conclusion that shells at a given outcrop are large b ased on a single sam ple from that outcrop when, in fact, m ost shells at that outcrop w ere small, then one would be making an erroneous conclusion b ased on an inaccurate, or insufficient sam pling strategy. In sum , the degree of resolution which can be expected from the outcrop under study n eed s to be ad d ressed in order to confirm that single sam ples, double sam ples, float, or m useum specim ens can provide a representative sam ple of the studied outcrop which can be used in long-term analyses of predator-prey interactions. Unfortunately, studies of lateral variability and sam pling reproducibility which a d d re ss potential biases in large-scale predation studies are few and far 11 betw een (but s e e Stanton and Evans, 1972; Schindel, 1980, 1982; Koch, 1987; Koch and Morgan, 1988; Miller 1988, 1989; C oB abe and Allmon, 1994; and H ansen and Kelley, in press). With this in mind, this study exam ines patterns of lateral variability at several different scales in order to determ ine: i) if lateral variability is a pervasive feature of fossil deposits which are commonly sam pled in large-scale predation studies; ii) on what sc ales it exists; and iii) to what extent it might affect vertical- or tem porally-based sam ple collection strategies em ployed in aforem entioned large-scale predation studies. O ne of the sim plest w ays to m ake an a sse ssm e n t of this lateral variability is to exam ine variability at a sm all-scale within one taxonom ic group during one time period. In this preliminary study (described in m ore detail below), small- scale variability w as exam ined at a variety of scales ranging from individual sam ples to multiple form ations utilizing abundant specim ens of the genus Turritellidae (Fig. 1). Studied sam ples, outcrops and form ations are from the sam e epoch and represent similar paleoenvironm ents (for m ore detailed descriptions, s e e Geologic Setting below). Seven sam pling localities of five different Gulf C oastal form ations w ere chosen for this study for a variety of reasons, including: i) relative e a s e of access; ii) they have been well studied in stratigraphic and depositional contexts--thus they are temporally and paleoenvironm entally well-constrained; iii) they represent similar shallow-water paleoenvironm ents; iv) they are characterized by similar styles of deposition and have similar styles (but varying degrees) of fossil condensation and community tim e-averaging; v) faunas of th e se localities have been the focus of much previous work and hence are well described; and vi) faunas from th ese localities have been utilized in a num ber of 12 large-scale studies of predator-prey interactions (e.g., Toulmin, 1977; Vermeij, 1977, 1982, 1987; Dudley and Vermeij, 1978; Dockery, 1988; Vermeij et al., 1980; Allmon, 1988a; Allmon et al., 1990; Allmon and Dockery, 1992; Kelley and H ansen, 1993; C oB abe and Allmon, 1994; H ansen and Kelley, in press). To ad d ress lateral variability within outcrops of th ese formations, at each locality, a num ber of bulk sam ples w ere rem oved from a variety of locations along a transect of a single fossiiiferous horizon. Although lateral variability m ay likely exist in tw o-dim ensions within a given horizon, this variability is difficult to ad d ress except in c a s e s of large bedding plane exposures and is hence not ad d ressed in this study. In addition, sm all-scale vertical variability m ay exist at a given outcrop (i.e., betw een sam pling horizons) but is not a d d ressed in this study b ecau se it is often noted in predation studies which em phasize fine-scale vertical sam pling (e.g., Kelley, 1988, 1989, 1992, and references therein) B ecause paleobiological studies (including studies of predator-prey interactions) m ay be significantly affected by variations in sam ple size (Koch & Sohl, 1983; Koch, 1987; Koch & Morgan, 1988), sam ples collected in this study are of roughly the sam e size (two-liter volumes). This sam pling size w as chosen b ecau se it provided enough individuals to m ake statistically significant com parisons betw een and within abundant, com m on taxa (CoBabe and Allmon, 1994), and b ecau se sam ples w ere not so large a s to m ake this pilot study intractable in the context of a M.S. thesis. Turritelline gastropods (including the g en era Mesalia and Turritella; Marwick, 1957) w ere chosen a s the focus group for this study because: i) they are numerically abundant and taxonomically diverse in all of the sam ple 13 localities; ii) their taxonom ic affinity and functional morphology is relatively well- constrained a s a result of earlier studies; iii) they have been utilized in a num ber of large-scale paleobiologic and paleoecologic studies; and iv) they commonly preserve information about other organism s (such a s predatory gastropods, crabs, and assorted epibionts) which m ay have interacted with them during and/or after their lifecycle (e.g., Marwick, 1957; Carriker and Yochelson, 1969; Toulmin, 1977; Vermeij, 1977; Dudley and Vermeij, 1978; Dockery, 1980; Allmon, 1988a; Allmon et al., 1990; Kelley and H ansen, 1993; Allmon, 1994). S pecim ens in this study w ere m easured for a variety of param eters which have been utilized in other large-scale predation studies (e.g., A degoke and T evesz, 1974; Vermeij, 1977; Dudley and Vermeij, 1978; Vemeij et al., 1980; Kitchell et al., 1981; Taylor et al., 1983; Kabat and Kohn, 1986; Kitchell, 1986; Vermeij, 1987; Kelley, 1988, 1989; Allmon et al., 1990; A nderson, 1992; Kelley, 1992; Kelley and H ansen, 1993; Tull and B ohning-G aese, 1993; H ansen and Kelley, in press). T h ese param eters provide information about the prey organism s them selves a s well a s information about their interactions with other predatory organism s during and after death of the organism (e.g., Shim oyam a, 1979,1985; Shim oyam a et al., 1979; Frey, 1987; Smyth, 1988, 1989, 1990; Walker, 1986, 1988a, 1988b, 1989, 1990, 1992a). Information w as collected about the size of prey (in this case, the taxon under study), the size of predators, intensity and efficiency of predation in th ese comm unities, and d e g re es of post mortem shell degradation a s indicated by two generalized taphonom ic proxies (for further discussion of th ese param eters, s e e M ethods section below). Sm all-scale lateral variability (and hence reproducibility of sam pling strategies) w as exam ined within individual bulk sam ples from each outcrop by 14 assessin g differences betw een each species present in a given sam ple. Lateral variability betw een bulk sam ples at a given outcrop w as also a sse sse d by examining differences within and betw een given species across a given sampling horizon. Lateral variability w as a sse sse d at larger scales by examining variations betw een different outcrops of the sam e formation and betw een formations of similar age. Combination of sam ples from a variety of sources m ay introduce potential biases into large-scale predation studies which have not previously been addressed. U sage of sam ples which may have been collected in a different m anner or a different location (e.g., museum collections) together with sam ples collected directly from outcrops may introduce sam pling-based biases. To a s s e s s this potential bias and to suggest constraints for future usage of multiple data sources, field-based information from this study is com pared to similar information collected from a num ber of m useum collections utilized in previous large-scale studies of predation (Sohl, 1969; Vermeij, 1977, 1982, 1987; Dudley and Vermeij, 1978; Vermeij et al., 1980; Allmon et al., 1990; Anderson, 1992). Museum collections are analyzed for patterns of within- outcrop variability, and together with literature reports, are com pared to field- based results of this study. In addition, results from this study are com pared to results reported in several large-scale studies of predation in order to a sse ss effects of lateral variability on previously identified patterns of predator-prey interactions (Dudley and Vermeij, 1978; Allmon et al., 1990; Allmon and Dockery, 1992; Kelley and H ansen, 1993). Thus, by attempting to identify lateral variability in well- preserved fossil taxa in commonly utilized fossiliferous strata from the Gulf 15 C oast, this study hopes to aid in constraining potential biases which m ay affect aforem entioned (and future) large-scale studies of predator-prey interactions. In addition to potential b iases which m ay result from u sag e of simplified sam pling strategies, m ost of th e aforem entioned studies have utilized a variety of techniques to synthesize data from a variety of sources. T h ese are sum m arized in the M ethods section (below). Although th e se simplified techniques of d ata synthesis are often necessary in order to m ake generalizations about large-scale or long-term patterns, there are potential b iases in using them which have not been adequately a s s e s s e d in the literature. With this in mind, this study utilizes several techniques of data synthesis in order to illustrate potential hazards of commonly used data synthesis techniques in order to identify potential sources of bias so that future predation studies (as well a s readers of previous predation studies) can take this information into consideration when interpreting the results. 16 GEOLOGIC SETTING Fossils were collected from five formations at seven different outcrops in the Gulf C oast of the United States. Studied outcrops were targeted because of their accessibility, because they are temporally and paleoenvironmentally well- constrained as a result of earlier studies, and because sam ples from these localities are commonly found in museum collections and have been used by others in large-scale studies of predation. Ages of most strata in the Gulf Coast are based on biostratigraphic studies of calcareous nannoplankton, with the exception of the Stone City Beds, which have been correlated by mollusks and stratigraphic position (Dockery, 1980). For a more detailed summary of nannoplankton zones, se e Allmon (1988b). Sam ples were collected from fossiliferous horizons which represented broadly similar paleoenvironmental regimes in order to facilitate com parisons between sam ples. However, many of these paleoenvironmental interpretations are very general in nature, partially owing to lack of detailed studies. Many of the paleoenvironmental interpretations are no more detailed than descriptions of strata as representing "shallow shelf", "deltaic", or "open marine" environments (for further discussion, se e summary in Allmon, 1988b). Thus, although the grain-sizes of the study sam ples are variable (likely due to variable proximity to sedim ent sources, microenvironmental variations such a s proximity to lagoonal vs. high energy regimes, and/or winnowing of sediment), all of the studied sam ples have been interpreted to represent shallow near-shore marine environments. However, many of the sampled outcrops are characterized by glauconitic sands, suggesting that many of these beds were deposited under 17 transgressive conditions characterized by sediment starvation of shelf environments (Fischer, pers. comm.). Thus, there does not seem to be agreem ent on the specific depositional and taphonomic histories of each of the studied strata; sediments may have been deposited in shallow marine to open- shelf sediment-starved environments. Large-scale studies of predation take these paleoenvironmental generalizations into account and assum e temporal and paleoenvironmental equivalence of their sam ples in order to make comparisons between different units (and hence samples). Although this study's sam ples are from strata which differ slightly lithologically and temporally, I follow protocols of other large-scale predation studies in assuming that al! sam ples are from broadly similar paleoenvironments. Below I outline (chronologically) the salient geologic characteristics of the seven outcrops sampled in this study, including paleoenvironmental, stratigraphic, geologic, temporal, locality, faunal, and lithologic descriptions. For purposes of comparison, all study localities are indicated on a generalized locality map (Fig. 2). Studied strata are also indicated on a generalized composite stratigraphic section for the Gulf Coastal Region (Fig. 3). Stone City Beds The Middle Eocene (Claiborne Group) Stone City Beds were sampled at a locality in Burleson County, Texas. The Stone City Beds are a distinct unit which overlies and interfingers with the Sparta units and is composed of highly fossiliferous dark grey glauconitic clay (Toulmin, 1977). The Sparta Formation is a -1 5 m thick unit consisting of very fine-grained cross-bedded quartz sand Figure 2: Generalized locality map of the seven outcrops sampled in this study. (1=Brazos River, Texas; 2=Tcheva Creek, Mississippi; 3=LeFleur's Bluff, Mississippi; 4=West Talahalla Creek, Mississippi; 5=Chickasawhay River, Mississippi; 6=Litt!e Stave Creek, Alabama; 7=Tombigbee River, Alabama). For more detailed information, see individual locality maps (Figs. 5,7,9,11-13,15). FLORIDA PanhantU * A L A B A M A G E O R G IA LOUISIANA EA ST T E X A S ' / / 7 7 7 7 7 7 7 A Pdf'*** Mi-Tmoch fm C f j l l l l HlVfl f'TI M oody* 8r««ct> Fm M ilch o tig tx o Fm Figure 3: Generalized composite stratigraphic section of Tertiary units of the Gulf Coast. U.S.A. (from Dockery, 1980). 20 overlying -4 5 m of similar sands and carbonaceous sands and clays (Ricoy and Brown, 1977; Berg, 1979; Fig 4). The Stone City Beds in Texas are laterally equivalent to the middle portions of the Lisbon Formation (described below; Toulmin, 1977; Carter and Rossbach, 1989). At the studied locality, the Stone City Beds are -2 0 m thick and are characterized by dark grey marine shales interbedded with glauconitic fossiliferous bioturbated sandy lenses and horizons (Knight et al., 1977). T hese sedim ents were interpreted to be deposited during a progradational phase of a transgressive event (Berg, 1979) in a shallow shelf environment, possibly analogous to bays and open shelf areas east of the Mississippi delta (Stanton and Warme, 1971; Stanton and Evans, 1972). The Stone City Beds are highly fossiliferous, including a number of invertebrate forms such a s gastropods, bivalves, scaphopods, serpulid worm tubes, bryozoans, and hexacorals, a s well as rare fragments of decapods, cephalopods, echinoids, ophiuroids, chitons, barnacles, sponges, and brachiopods (Knight et al., 1977). The unit also contains microfossils such as ostracods and foraminifera, vertebrate fossils such as fish and ray teeth, bones, scales, otoliths, and dermal plates, terrestrial fossils such as insects, plants, spores, and pollen, and trace fossils (Knight et al., 1977; and references therein). At the study locality (which is also the type locality for this formation), shell-rich horizons of marine origin are commonly exposed along the bluffs on the northern edge of the Brazos River (Fig. 5). The main fossiliferous horizon (which w as sampled for this study) is about 1.5 m thick and occurs in the upper third of the section exposed at the Brazos River locality (for a more detailed description, se e Stanton and Nelson, 1980). 21 Crockett Fm. Main Glauconite Bed _ c o o u. O t o c o C O m -* » -* • Sparta Fm Figure 4: G eneralized stratigraphic section for the Stone City Beds at the B razos River locality (modified from Stanton and Nelson, 1980). Study sam ples are extracted from the main glauconite bed. 22 Kilometers ■ Little * Brazos R Brazos River Figure 5: Locality map for the Stone City Beds of the Sparta Formation at theBrazos River, Texas. For more detailed localitiy information, se e Knight et al. (1977). Arrow indicates sampling site on south bank of river. Locality is the sam e a s Texas BEG loc. 26-T-1, PRI loc. 723, and USGS 5473. 23 Lisbon Formation The Middle Eocene (Claiborne Group) Lisbon Formation w as sam pled at a locality in Clarke County, Alabama. The Lisbon Formation disconformably overlies the Tallahatta Formation and is disconformably overlain by the Gosport Sand. The Lisbon Formation is usually separated into three units, including the Lower, Middle, and Upper units (Toulmin, 1977; Fig. 6). The Lower Lisbon is -3-6 m thick and consists of coarse-grained, glauconitic sand; the Middle Lisbon consists of -2 5 m of carbonaceous to lignitic sand and silty clay; the Upper Lisbon is variable in thickness (from 0 to 50 m) and may consist of greenish-grey sandy clay with interbeds of yellowish-grey calcareous sand (Toulmin, 1977; Allmon, 1988b). In the studied region, the Upper Lisbon Formation is well exposed and primarily consists of calcareous sand, glauconitic sandy marl, and sandy marine clays. The sandy units (from which this study's sam ples were collected) have been interpreted to represent a shallow near-shore marine environment (i.e., Gardner, 1957; Oman, 1965, 1966; Toulmin, 1977; Dockery, 1980). The Lisbon Formation is highly fossiliferous, and has a diverse assem blage which is dominated by gastropods and bivalves, and is also characterized by solitary corals, shark teeth, oysters (including the guide fossil Cubitostrea sellaeformis in the upper member), and oyster biostromes (Toulmin, 1977; Dockery, 1980; and references therein). Study sam ples were collected from a sandy horizon in the upper part of the Lisbon Formation located along the eastern margin of the Tombigbee River (Fig. 7). 24 ■ a c CD CO tr o a. v > o a J_1 • ‘ V 0) a. Q. 3 o X I ( A ja » ■ a ■ o 5 o - 7 Clay Sand CaCOc 7 7 Glauconite Not Present @ Study Site Figure 6 : G eneralized stratigraphic section for the Lisbon Formation (modified after Toulmin, 1977). T hicknesses a re not to scale. 25 Tombigbee River \ Coffeeville AL Kilometers 0.6 1.2 Figure 7: Locality map for the Lisbon Formation at theTombigbee River, Alabama. Arrow indicates sampling site on east bank of river. Locality is located in sections 8 and 17, T9N, R1W of the Clarke County, Coffeeville 7.5 minute quadrangle. Locality is the sam e a s USGS 12181 and Toulmin (1977) ACI-3. 26 Gosport Sand The Middle Eocene (Claiborne Group) Gosport Sand w as sam pled at a locality in Clarke County, Alabama. The Gosport Sand disconformably overlies the Lisbon Formation (with a potential gap of 0.6 my — com pare with estim ated interval of <0.5 my for entire Gosport; Hazel et al., 1984; Allmon, 1988b) and is unconformably overlain by the Moodys Branch Formation. The contact betw een the Gosport and the Lisbon Formation is characterized by burrows into the Lisbon which are filled with sand from the Gosport (Toulmin, 1977 and references therein). In general, the Gosport Sand is about 2 -6 m thick, and consists of extremely fossiliferous glauconitic quartz san d with occasional thin lenses of carbonaceous shale and lignite (Copeland, 1968; Toulmin, 1977; Fig. 8 ). Sam ples w ere collected at Little Stave Creek, a locality fam ous for its exposures of Eocene Gulf Coast strata (Fig. 9). At this locality, the Gosport is characterized by an abundant m olluscan fauna dominated by bivalves and gastropods, a s well a s rare solitary corals and bryozoans. Microfauna include foraminifera and ostracods. The Gosport is thought to have been deposited a s part of a transgressive sequence and is interpreted to represent a shallow near shore environm ent (Dockery, 1987). This interpretation is suggested by the presence of leaf-bearing clays which locally overlie, underlie, and interfinger with the sandy shell-beds. The basal sand of the Gosport is characterized by poorly sorted grains of quartz and glauconite and contains abundant worn and broken shark teeth (Toulmin, 1977). Sam ples were collected from a horizon located approximately one m eter above the basal sand of the Gosport at a locality along the margin of Little Stave Creek (for more information about this locality, se e Gardner, 1957). Thickness (meters) 27 Moodys Branch Fm . & JL Clay Sand 7 7 | Glauconite Ironstone Concretion Fossils $$ I Trace Fossils Lisbon Fm Figure 8: Generalized stratigraphic section for the Gosport Sand in Clarke Co., Alabama (modified after Toulmin, 1977). Thicknesses are approximate. Entire unit is extremely fossiliferous. 28 Kilometers I ■ ■ ■ 0.3 0.6 * % \ i \ ♦ ♦ Little * StaveC Creek ^ ;□ ! I □ N / west ♦Point Drive Jackson Figure 9: Locality map for the Gosport Sand at Little Stave Creek, Alabama. For more detailed information, see G ardner (1957). Arrow indicates sampling site. Locality is located in sections 20 and 29, T7N, R2E, of the Burleson County, Jackson 7.5 minute quadrangle. 29 Moodys Branch Formation The Upper Eocene (Jackson Group) Moodys Branch Formation w as sam pled at three different localities in Clarke, Hinds, and Yazoo Counties, Mississippi. The Moodys Branch Formation overlies the Cockfield Formation (m ade up of deltaic sedim ents equivalent to the Gosport Sand in Alabama) and is overlain by the North Twistwood Creek Member (which is primarily com posed of clays) of the Yazoo Formation (Dockery, 1986a). In this region, the Moodys Branch Formation ranges from 3 to 6 m in thickness (Mellen, 1940; Allmon, 1988b) and is com posed of fossiliferous glauconitic san d s and clayey sands which have been subdivided into two laterally-distinct facies, known a s the northern and southern terrigenous facies (Dockery, 1976, 1977; Fig. 10). Strata from Hinds and Yazoo Counties contain the stratigraphically lower northern terrigenous facies and have been interpreted to represent nearshore shelf sedim ents. Strata from Clarke County contain the stratigraphically higher southern terrrigenous facies and have been interpreted to represent shelf sedim ents from slightly further offshore. The northern facies can be divided vertically into two distinct lithologic units. The upper unit is often characterized by marls and brownish glauconitic clayey sands. The lower unit is sand- dom inated and fossiliferous, often with light-brown calcareous san d s in the upper portions and brown san d s in the basal portions (Dockery, 1980, 1986a). Fossils are found throughout the Moodys Branch Formation and include a diverse assem blage of gastropods, bivalves, corals, and other fauna (Dockery, 1977; 1980). In Hinds County, sam ples were collected from the lower sandy m em ber at LeFleur's Bluff State Park (also known a s Riverside Park) in the deep ravine along the Nature Trail (Fig. 11). This locality, called Fossil Gulch, is 30 Scale in meters Sand EE3 Clay | — | Calcareous Fossils _ l j j > | Trace Fossils n** ! Ironstone Concretion Figure 10: Generalized stratigraphic section for the Moodys Branch Formation. Modified from a measured section of Dockery (1980) taken along the Chickasawhay River, Mississippi. Thicknesses are approximate. 31 Pearl River MS 55 Kilometers 0.3 0.6 Figure 11: Locality map for the Moodys Branch Formation at LeFleur's Bluff in Riverside Park (lightly shaded), Mississippi. Entire map a re a is within Jackson city limits. For more detailed information, se e Dockery (1986b). Arrow indicates sampling site. Locality is located in section 36, NEV4 NWV4 NWi/4„ , T6 N, R1E, Hinds County, Jackson 7.5 minute quadrangle. Locality is the sam e a s MGS 2. 32 fam ous because it is one of the last protected exposures of the entire Moodys Branch Formation [see Dockery (1986b) for more detailed information on this locality]. Sam ples were collected from one horizon in the middle of the Moodys Branch strata exposed along the margins of Fossil Gulch. In Yazoo County, sam ples were collected from a locality along the western to northwestern margin of Tcheva Creek (Fig. 12). Sam ples were extracted from a thin (-20-30 cm) horizon in the basal unit of a fossiliferous glauconitic clayey sand of the northern facies. This unit has been interpreted to represent an assem blage with w as deposited during a transition from high energy wave or tidal conditions to open-m arine conditions (Dockery, 1977). In Clarke County, sam ples were extracted from a locality along the eastern margin of the Chickasawhay River, near the Bridge Gun & Hunting Club (Fig. 13). Sam ples were extracted from a highly fossiliferous horizon near the boat-launching area of the Gun Club. B ecause this horizon w as characterized by sand and w as highly fossiliferous, it is inferred to represent the glauconitic sand layer of the southern facies. Byram Formation The Lower Oligocene (Vicksburg Group) Byram Formation w as sam pled at a locality in Smith County, Mississippi. The Byram Formation overlies the Glendon Limestone and underlies the Bucatunna Formation and together with th ese units, has been interpreted to be part of a coastal onlap cycle (Baum and Vail, 1988). Depending on the interpretation of the sequence boundary of the underlying units, the fossiliferous Byram units are thought to constitute the regressive phase of this cycle (Allmon and Dockery, 1992). In general, the Byram Formation is a glauconitic clayey sand unit characterized by a well- 33 Midway A Tcheva Creek Kilometers « ■ » Figure 12: Locality map for the Moodys Branch Formation at Tcheva Creek, Mississippi. Arrow indicates sampling site. Locality is in section 32, SW 1/4 SWV4, T13N, R1E of the Yazoo County, Mississippi quadrangle. Locality is the sam e as MGS 11. 3 4 Bridge Gun & Hunting Club Chickasawhay iRiver Shubuta MS 9 m Kilometers 0.5 0.6 Figure 13: Locality m ap for the Moodys Branch Formation at the C hickasaw hay River, Mississippi. Arrow indicates sam pling site. Locality is in section 30, NWV4 NE1/4 SEV4, T1N, R16E of the Clarke County, Mississippi quadrangle. Locality is the sam e a s MGS 16. 35 preserved m olluscan fau n a (Fig. 14). At th e study locality, a layer of the upper part of th e Byram Form ation is well exposed along th e south and southeastern m argin of W est T alahalla C reek (Fig. 15). At W est Talahalla Creek, an exceptional turritelline-dom inated assem b lag e occurs in a dark grey sa n d y clay unit which is exposed along the margin and bed of th e creek. This a ssem b lag e is thought to have been deposited in a shallow near-shore environm ent (Fisher and W ard, 1984) characterized by oscillatory cu rren ts and possibly fluctuating salinities (Allmon and Dockery, 1992). This locality is dom inated by T. mississippiensis C onrad, with rare occu rren ces of Turbinelfa witsoni C onrad and fragm entary sm all bivalves (Allmon and Dockery, 1992). In addition to m acrofauna, a benthic foraminiferal a sse m b la g e dom inated by rotaliines and an ostracod a sse m b la g e dom inated by th e family C ytherideidae are also p resen t (Allmon and Dockery, 1992). T he turritelline a sse m b la g e is by far the m ost conspicuous a sp e c t of this locality, a s all Turritella shells are extrem ely well preserved, a re oriented in a bimodal distribution, and a re p resen t in an otherw ise "sparsely fossiliferous" 1-5 cm thick layer (for a m ore detailed description of this locality, s e e Allmon and Dockery, 1992). S am ples used in this study w ere collected from this layer. 36 P L C f f tT - o c e w t IMM O ll U C B f l l l l 'Thickness (meters) te p ld o c u lln i Figure 14: Generalized stratigraphic section for the Vicksburg Group, including the Byram Formation (from Fisher and Ward, 1984). Section w as m easured at the Mississippi Vatley Portland Cement Company quarry (NWV4 Section 26, T18N, R4E), three miles northeast of Redwood on Mississippi Highway 3. 3 7 Leaf River /W e s t f Tallahala Creek Sylvarena Kilometers Figure 15: Locality m ap for th e Byram Formation at W est Talahalla C reek, M ississippi (modified after Allmon and Dockery, 1992). Arrow indicates sam pling site. Locality is in section 5, T1N, R9E of the Smith County, C enter Ridge 7.5 minute quadrangle in th e T alahalla C reek Oil and G as Field. Locality is the sam e a s MGS 94. 38 METHODS Field Sampling Strategy Multiple bulk sam ples w ere collected from each outcrop under study. Two-liter volum es of sedim ent w ere rem oved from the host lithology using a trowel and a shovel, with care not to break up the sedim ent sam ple or its asso ciated fossils. Sam ples w ere then w rapped tightly in plastic b ag s to prevent sam ples from drying out and breaking apart. At each different outcrop, multiple (range: 2-12) sam ples w ere collected from one -2 0 cm - thick horizon. Fossiliferous horizons w ere selected for study in order to insure large fossil abundances for study. Fossiliferous horizons at all of the study localities represent condensed shell-beds. The d eg ree of condensation affects each unit differently with respect to the tim e-averaging, taphonom y, and depositional history of constituent fossils (for a sum m ary, s e e Allmon, 1988a). Variations in th ese factors m ay affect com parisons betw een units and are a d d ressed in the Discussion section. However, b ecau se m ost aforem entioned large-scale predation studies com bine sam ples from the sam e outcrops and units utilized in this study, this study follows a similar protocol. At all of the localities, sam ples w ere collected along a continuous lateral transect. The irregular nature of m any of the outcrops m ade sam pling along a straight linear transect difficult; therefore, sam ples w ere collected along a roughly linear transect, depending on outcrop accessibility. All sam ples are sp aced at roughly 5 m intervals, (with the exception of the sam ples from W est Talahalla Creek, which w ere spaced ~1 m apart) along a transect along the face of each exposed outcrop area. The num ber of sam ples collected varied 39 depending on outcrop size, outcrop accessibility, and ability to extract sam ples from the sam e laterally-identifiable horizon. All localities sam pled in this study are illustrated in Figure 1. The following sam ples were collected: 1) Six two-liter sam ples were extracted from one interval within the E ocene Gosport Sand (upper Claiborne Group) at a locality along Little Stave Creek in Clarke County, Mississippi. 2) Nine two-liter sam ples w ere extracted from one interval within the Eocene Moodys Branch Formation (lower Jackson Group) at a locality along Tcheva Creek in Yazoo County, Mississippi. 3) Five two-liter sam ples w ere also extracted from exposures of the Moodys Branch Formation at a locality along the Chickasawhay River in Clarke County, Mississippi. 4) Three two-liter sam ples w ere also extracted from exposures of the Moodys Branch Formation at a locality at LeFleur's Bluff State Park in Hinds County, Mississippi. 5) Two two-liter sam ples were extracted from one interval within the E ocene Lisbon Formation (middle Claiborne Group) at a locality along the Tombigbee River in Clarke County, Alabama. 6 ) Five two-liter sam ples were extracted from one interval within the E ocene Stone City Beds (middle Claiborne Group) at a locality along the Brazos River in Burleson County, Texas. 7) Twelve two-liter sam ples were extracted from one interval within the Lower Oligocene Byram Formation at a locality along W est Talahalla Creek in Smith County, Mississippi. 40 In addition to the two-iiter sam ples utilized in this study, replicate two-liter sam ples were collected at the sam e bulk sam ple sites at each outcrop in order to identify: i) reproducibility of results at each sampling location; and ii) potential biases which might be incurred in sam ple transport, disaggregation, and fossil preparation (e.g., Flessa et al., 1992). Laboratory Processing and Data Collection Strategy Bulk sam ples were disaggregated in the laboratory using several techniques. Sam ples with high sand contents, (including sam ples from the Gosport and Lisbon Formations), were easily disaggregated by immersing them in water in an ultrasonic basin for 5 to 15 minutes (e.g., Pojeta and Balanc, 1989; and references therein). Sam ples which were clay-based, (including sam ples from the Byram, Moodys Branch, and Stone City Formations), were more difficult to disaggregate because of their high organic content. Sam ples from these three formations were first dried slowly (for several days) in a low- tem perature oven (at 50° C) and then soaked in bleach for approximately 12 hours (e.g., Harris and Sweet, 1989; and references therein). The bleach was then decanted from the sam ples. Sam ples from the Moodys Branch and Stone City Formations were then placed in an ultrasonic basin (filled with water) for 5 to 30 minutes in order to facilitate breakup of the sedim ents (Pojeta and Balanc, 1989; and references therein). Sam ples from the Byram Formation contained very fragile shells and thus were not placed in the ultrasonic basin. After decanting the liquid from all sam ples, they were allowed to dry for 24 to 48 hours at room temperature. 41 Fossil shells were then picked from the matrix of each sample by using tweezers or an artist's paintbrush with the aid of a magnifying lamp. All turritelline gastropods and naticids or muricids were extracted from each sample and identified to the species level based on comparison to previously published descriptions (e.g., Dockery, 1977, 1980; Toulmin, 1977; MacNeil and Dockery, 1984). In large-scale studies of predation, paleobiological information is commonly collected about predator and prey characteristics (e.g., size) as well as about their behavior (e.g., information about other organisms' drilling and peeling attempts on the study shells; Adegoke and Tevesz, 1974; Vermeij, 1977; Dudley and Vermeij, 1978; Vemeij et al., 1980; Kitchell et al., 1981; Taylor et al., 1983; Kabat and Kohn, 1986; Kitchell, 1986; Vermeij, 1987; Kelley, 1988, 1989; Allmon et al., 1990; Anderson, 1992; Kelley, 1992; Kelley and Hansen, 1993; Tull and Bohning-Gaese, 1993; Hansen and Kelley, in press; and references therein). Other studies of molluscan fauna from the Gulf Coast have also demonstrated the utility of noting taphonomic characteristics of the study shells (such as shell breakage and epibiont characteristics) in order to gain information about the post-mortem history of the shells (e.g., Shimoyama, 1979,1985; Shimoyama et al., 1979; Frey, 1987; Smyth, 1988, 1989, 1990; Walker, 1986, 1988a, 1988b, 1989, 1990, 1992a; and references therein). This information can be used to constrain potential biases in predation studies resulting from post-mortem predator-prey interactions (e.g., Walker, 1992a,b). With this in mind, the param eters and methods of m easurem ent utilized in this study are illustrated in Figure 17. Shell length and width were m easured because they are proxies for prey size (e.g., Dudley and Vermeij, 1978; Allmon 42 2 Figure 16: Param eters m easured in this study. (A=Maximum Whorl Diameter; B=Drillhole Diameter; C=lncomplete Drillhole; D= Healed Peel-mark; E=Shell Length; Y-Y'=Cross-section Through Shell). 43 et al., 1990; Tull and Bdhning-G aese, 1993). Shell length and width {in the center of the largest maximum whorl) w ere m easured utilizing digital calipers (precision = 0.01 mm). Shell width (i.e., maximum whorl diam eter) is typically a better proxy for shell size b ecau se shell breakage do es not prevent m easurem ent of this param eter (as opposed to length m easurem ents, which can often be ham pered by broken shell tips). The maximum width of drilling sites w as also m easured b ecau se the size of drillholes h as been dem onstrated to be a proxy for predator size (e.g., Kitchell et al., 1981; R abat and Kohn, 1986; Palm er, 1988, 1990). P resen ce of drillholes and peeling m arks w as noted in the study shells b e ca u se they give information about the activities of predatory organism s (in this case , drilling gastropods and peeling crabs) which prey upon turritelline gastropods (e.g., Carriker and Yochelson, 1968; Sohl, 1969; Adegoke and T evesz, 1974; Vermeij, 1977; Vermeij et al., 1981). Like other large-scale studies of predation (e.g., Adegoke and Tevesz, 1974; Vermeij, 1977; Dudley and Vermeij, 1978; Vemeij et al., 1980; Kitchell et al., 1981; Taylor et al., 1983; R abat and Kohn, 1986; Kitchell, 1986; Vermeij, 1987; Kelley, 1988, 1989; Allmon et al., 1990; Anderson, 1992; Kelley, 1992; Kelley and H ansen, 1993; Tull and Bohning-G aese, 1993) this study focuses on the predatory activities of shell-drilling naticid and muricid gastropods and shell-peeling calappid crabs. Attem pts at prey consum ption by th ese organism s a re recorded in th e fossil shells (e.g., Carriker and Yochelson, 1968; Sohl, 1969). As h as been done in other studies of predation (e.g., Adegoke and T evesz, 1974; Vermeij, 1977; Dudley and Vermeij, 1978; Vemeij et al., 1980; Taylor et al., 1983; R abat and Kohn, 1986; Vermeij, 1987; Kelley, 1988; Allmon et al., 1990; Anderson, 1992; 44 Kelley and H ansen, 1993; Tull and Bohning-G aese, 1993; H ansen and Kelley, in press), the record of drillholes and peel-m arks is used to estim ate the intensity and efficiency of predatory behavior in relation to the turritelline gastropod prey. Drilling intensity estim ates represent the percentage of shells which contain evidence of single successful drilling attem pts. Drilling intensity estim ates do not include multiply or incompletely drilled shells. Although they are often distinguishable (especially in larger shells; Carriker and Yochelson, 1968; Sohl, 1969), muricid and naticid drillholes are com bined in this study (following similar protocol se t by Dudley and Vermeij, 1978 and sub seq u en t large-scale predation studies listed above). Not all drilling attem pts result in successful consum ption of the prey, however. For exam ple, drilling activity m ay be interrupted prior to completion of the drillhole or empty shells m ay be repeatedly drilled (see review in Kelley and H ansen, 1993); this type of drilling activity represents inefficient predatory behavior b ecau se no "food" is collected a s a result of energy expenditure via drilling. Thus, drilling inefficiency estim ates represent the percentage of shells which contain evidence of unsuccessful drilling attem pts (i.e., all shells with multiple or incom plete drillsites; A degoke and Tevesz, 1974; Vermeij, 1982; Kitchell e ta l., 1981; Kitchell et al., 1986; Kabat and Kohn, 1986; Vermeij, 1987; Allmon et al., 1990; Tull and Bohning-G aese, 1993). Peeling intensity estim ates represent the percentage of shells which contain evidence of peeling attem pts (including repaired and unrepaired peeling marks; Vermeij, 1977; Vermeij et al., 1980; Vermeij et al., 1981; Vermeij, 1982; Allmon et al., 1990). Inefficient peeling estim ates w ere not m ade because: i) the num ber of recognizable successful 45 peeling attem pts is extremely small (<1 % of all peeled shells); and ii) successful peeling attem pts are not likely to be preserved b ecau se the shell aperture, when peeled successfully, is more fragile and hence likely to break off during shell transport, reworking, or burial (Walker, pers. comm.). G eneralized taphonom ic characteristics of the turritelline sam ples were also noted (including estim ates of shell breakage and presence of epibionts) b ecau se they have been shown to provide information about the post-mortem history of shell assem blages (e.g., Walker, 1988; and Walker, 1992a) and may provide clues on the m echanism s for patterns of lateral variability. Shells with evidence of breakage w ere noted. Shell breakage estim ates represent the percentage of shells which have evidence of non-healed breakage, such a s ab sen ce of shell tips or the basal whorl. Evidence for presence and type of epibionts w as noted by identification of characteristic markings on the shells (e.g., Walker, 1988a, b, 1989, 1990, 1992; and references therein). Epibiont presence estim ates represent the percentage of shells which have evidence of epibiont colonization (including presence of multiple epibionts). Epibiont evidence includes presence of scars, scratch-m arks, and indentations on shells which indicate the presence of bryozoans, corals, barnacles, or other colonizing organism s. Although the types of epibionts w ere identified on each shell, epibiont presence/absence w as utilized in this study in order to enable betw een-sam ple com parisons of the relative degree of epibiont colonization on shell sam ples. 46 Museum Collections Museum collections (including bulk sam ple-based collections) were examined in order to make comparisons to this study's outcrop-based observations. A similar suite of param eters was m easured on museum sam ples which were collected from the sam e outcrops utilized in the field-based portion of this study. Only taxa which were the sam e as those collected in the field were used. Mixed-species formation "averages'1 were calculated for each formation (for each study parameter) by combining averages for constituent taxa. Data Analysis & Presentation In order to a sse s large-scale patterns, previous studies have employed a variety of techniques to synthesize results from a variety of sam ples into one value (or m ean) for the interval under study. For example, previous large-scale predation studies have calculated m ean values (e.g., for levels of drilling, peeling, shell size, etc.) of a given formation or epoch in three different ways, including i) averaging all specim ens together (combining different num bers of different species) to obtain a mean for the interval under study (e.g., Adegoke and Tevesz, 1974; Dudley and Vermeij, 1978; Vermeij et al., 1980; Kitchell, 1986; Allmon et al., 1990; Hansen and Kelley, in press); ii) averaging all species together, with each species within a sam ple contributing equally to the sam ple mean, regardless of abundance of different taxa (e.g., Vermeij, 1987); and iii) assessing each species independently (e.g., Kitchell et al., 1981; Taylor et al., 1983; Kabat and Kohn, 1986; Kelley, 1988,1989,1992; Anderson, 1992; Tull and Bohning-Gaese, 1993). 47 Although examination of long-term patterns necessitates this type of taxonomic homogenization, sometimes combination of values for different species, such a s i) or ii) above, may bias results, especially when uncommon taxa have extreme values. Thus, two approaches are used in this study in order to circumvent these types of problems and to more accurately identify patterns of lateral variability. Within each of the sections described above, sam ple characteristics are summarized by values derived from all of the species within that sam ple (labeled Mixed Species variability), and by isolating each species in that sam ple (labeled Within Species variability). Mixed Species U sage of mixed species results in this study is similar to multiple-taxa averages used by Vermeij (1987) and others. In this study, mixed species values for each sam ple represent the m ean of the average value for each species within a sample, even though m easured populations for each species from each sam ple are different. For example, a sam ple containing three taxa (with average lengths of 5 mm, 10 mm, and 15 mm) might produce a mixed species average length of 10 mm for that sample. Within sam ple variability is a sse sse d by analyzing the variance (ANOVA) between the m ean value for each species within that sample. Between sam ple variability is a sse ssed by analyzing the variance between the m ean values for all sam ples within each outcrop. Between outcrop variability is assessed by analyzing the variance between the m ean values for each outcrop of the sam e formation. Between formation variability is a sse ssed by analyzing the variance between all m ean sam ple averages for each formation of similar age. Four formations of broadly 48 sim ilar a g e (all are E ocene and range from middle Claibornian to lower Jack so n ian in age) are com pared to one another. T he tim e gap betw een th e se form ations is -5 -7 million years (C arter and R ossbach, 1989). Many large-scale predation studies com bine information from multiple form ations (from different sta g e s) in order to obtain a value for that epoch and in order to a s s e s s longer- term patterns (e.g., Sohl, 1969; Vermeij, 1977,1987; Dudley and Vermeij, 1978; Vermeij et al., 1980; Kitchell, 1986; Allmon et al., 1990; A nderson, 1992). In the sa m e vein, this study also com bines results from multiple form ations in order to a s s e s s larger-scale (i.e., formation-level) patterns of lateral variability. Within S p e c ie s This study's u sa g e of within sp ecies results is analogous to within- sp e c ie s a n aly ses em ployed by Kitchell et al. (1981), Taylor et al. (1983), Kabat and Kohn (1986), Kelley (1988), Kelley (1989), A nderson (1992), Kelley (1992), Tull and B ohning-G aese (1993), and others. Within sp e cie s values for each sam ple rep resen t the m ean of all m easured specim ens (of that sp ecies) within that sam ple. Betw een sam ple variability is a s s e s s e d by analyzing the variance (ANOVA) betw een the m ean values for that taxon in each sam ple within an outcrop. In addition to the sam ples utilized in the mixed sp e cie s analyses, sam p les from the Lower O ligocene By ram Formation (i.e., T. mississippiensis) w ere used. B etw een outcrop variability w as a s s e s s e d by analyzing the variance betw een m ean values of that sp ecies for each outcrop. B etw een formation variability w as a s s e s s e d by analyzing the variance betw een all m ean sam ple av erag e s for that sp e cie s for each formation. R esults are organized into four sections, including predator and prey size characteristics, drilling and peeling 49 predation characteristics, taphonom ic characteristics, and m useum collection information. Statistical A pproaches O ne-w ay analyses of variance (ANOVA) w ere calculated for all d a ta s e ts in this study by using Microsoft Excel (v. 4.0) m acros on a M acintosh com puter (for m ore information about the ANOVA m acros, s e e [Microsoft], 1993). Analysis of variance determ ines w hether th e m ean s of a group of sam p les differ from one another b a sed on: i) partitioning of the sum of squares; and ii) estim ating of the stan d ard deviation of the population by two m ethods and a com parison of th e se e stim ates (Alder and R oessler, 1977). In order to utilize this test, it is a ssu m e d that all sam p les are taken from normally distributed populations. S am p les which did not contain m ore than one specim en (or d a ta point) w ere not analyzed for variance and are noted below in the results section. S am ples in which all th e values w ere the sam e w ere also not analyzed for variability (b ecau se there w as no variance) but are n o n eth eless reported below. Only significant variability above the 95% confidence level is reported in the results section. Variability above the 95% confidence level (p<0.05) is described a s significant. Variability above the 99% confidence level (p<0.01) is described a s highly significant. Variability above th e 99.9% confidence level (p<0 .0 0 1 ) is described a s very highly significant. In order to calculate probabilities (reported in the D iscussion section) of detecting significant variability am ong sam ple populations, it is a ssu m e d that: i) only the studied param eters, taxa, and outcrops are utilized for analysis; ii) sim ilar sam ple collection, distribution, and processing techniques are 50 em ployed; and iii) the sam e quantity of sam ples are collected. Probabilities are calculated by a sse ssin g the percentage of available study sam ples which exhibit significant variability and are expressed a s percent probability (out of 1 0 0 %) of encountering significant variability am ong similarly studied sam ples. Probabilities represent the likelihood of encountering significant variability in any given sam ple or param eter, assum ing that the sam ple and param eter are chosen independently and randomly. However, b ecau se future studies m ay sam ple in slightly different locations at a given outcrop (as this study did with respect to previous predation studies), one should only extrapolate and/or interpret reported probabilities in the general se n se (i.e., a s high or low probabilities), rather than a s absolute num bers. 51 RESULTS Results of these preliminary lateral variability studies are organized into five sections: i) sampling reproducability; ii) predator and prey size characteristics; iii) predation characteristics; iv) taphonom ic characteristics; and v) m useum collections. Param eters ii) through iv) w ere selected for study because they have been used in previous large-scale predation studies and b ecau se they provide easily-collected and easily-com parable information about the paleobiologic, paleoecologic, and taphonom ic characteristics of the turritelline gastropod shells used in this study. Predator and prey size characteristics include two estim ates of prey size, including the length and width of prey shells, and one estim ate of predator size {i.e., the diam eter of the drilling site). Although crabs are also predators, estim ates of their size are not available based on peel-m arks on prey shells. Predation characteristics include two estim ates of drilling predation, including the percent of shells drilled and the efficiency of shell drilling, a s well a s one estim ate of peeling predation (i.e., the percent of shells which have peel-marks). Generalized taphonomic features are also characterized by observing the percentage of shells which are broken and the percentage which have evidence of epibiont coverage. The m useum collections section includes analysis of ii), iii), and iv) on m useum specim ens which are com parable to field-based data collected in this study. Within each of these sections, lateral variability is examined: i) via mixed- species averages, and ii) via examination of patterns in individual species. Lateral variability is exam ined betw een constituent taxa in each two-liter sam ple. Lateral variability is also analyzed by using m ixed-species averages and is exam ined at the following scales: 52 i) Between two-liter sam ples at a given outcrop. ii) Between different outcrops of the sam e formation. iii) Between different formations of similar age. Lateral variability within individual species is analyzed betw een different sam ples at a given outcrop, between outcrops of the sam e formation, and between formations of similar age. Variability between taxa is examined in m useum collections. M useum-based results are also com pared to outcrop- based results. Sampling Reproducability In addition to the two-liter sam ples utilized in this study, replicate two-liter sam ples were collected at the sam e bulk sam ple sites at each outcrop in order to identify sampling reproducibility and potential sam ple preparation biases (e.g., Flessa et al., 1992). Replicate sam ples were analyzed by for the sam e param eters a s all primary sam ples and do not exhibit any significant differences in any of the param eters (for all 8 m easured param eters, p < 0.05, n=7). This suggests that sam ple transport and processing artifacts, if any, affect all sam ples in the sam e fashion. Although replicate sampling suggests reproducibility of results, sam ples collected from the W est Talahalla Creek outcrop of the Byram Formation may be subject to variations in outcrop-to-laboratory preservation (for a more detailed explanation, see Flessa et al., 1992). Shells from this deposit are very fragile and hence many were broken in the process of transporting and disaggregating sam ples. Thus, many of the shells from this outcrop could not be utilized in this 53 study, particularly for estim ates of prey size and shell breakage. Significant differences thus m ay exist betw een the am ount of shells available for study in- situ at th e outcrop and shells available for study from this study's sub-sam ples. However, replicate sam p les at the sam e location along th e lateral tran sect indicate that this bias affects all sam p les in roughly th e sa m e m anner. C om parison of all m easured p aram eters from replicate sam p les yield results which are not significantly different from one another (p < 0.05, n=7). Predator and Prey Size Characteristics B etw een S pecies: Within S am p les Stone City Beds Five two-liter sam p les of the S tone City B eds w ere collected from an outcrop along the B razos River in T exas (Figs. 4,5) and contain two sp ecies of turritelline gastropods, Mesalia claibornensis and Turritella nasuta (Fig. 17a,i). A verage length estim ates range from 5.66 mm to 16.91 mm for M. claibornensis (n=5; Table 1) and from 4.31 mm to 11.08 mm for T. nasuta (n=5). M easured sam ple siz e s range from 18 to 162 shells per two-liter sam ple (n=245). C om parisons of shell length betw een th e se sp ecies (within each sam ple) su g g e st that significant differences betw een constituent tax a do not exist in 4 of th e 5 sam ples. O ne sam ple exhibits a high level of significant variability betw een tax a (p<0.01). A verage whorl diam eter estim ates range from 3.32 mm to 5.74 mm for M. claibornensis (n-5) and from 1.25 mm to 2.50 mm for T. nasuta (n=5). M easured sam ple sizes range from 28 to 267 shells per two-liter sam ple (n=393). Four of five sam p les exhibit significant variations betw een Figure 17: Tumtelline gastropods utilized in this study. A = M. daibomensisf (x2.5); B = M vetusta** (x1.5); C = 7 apita** (x1.5); D = T . alveatat (xl.4); E= 7. ca/rnafa**(x1.5); F = 7 fischert* (x1.5);G = 7 ghignat* (x1.5);H= 7 mississippiensis * * * (x1); l= 7 nasut$ (x2.5); J = 7 obnita * * (x1.5); K = 7 perdita* * (x1.5). (* = Photograph from Dockery, 1980; * * = Photograph from Toulmin, 1977; * * * = Photograph from MacNeil and Dockery, 1984). m Table 1 : Predator and prey size characteristics. Mean values ( i n mm) and sample sizes for all studied taxa. Taxon Formation {Outcrop) Sam ple # Mean Length Specim ens 1 Mean WD Specimens Diameter Specim ens M. claibornensis Lisbon 1 2.91 2 1.26 2 0.71 1 2 17.62 50 6.5 53 1.28 25 M. claibornensis Stone City 1 9.1 6 5.19 10 1.22 2 2 16.91 2 5.74 3 1.31 1 3 8.7 43 | 4.56 81 0.79 8 4 6.66 6 j 3.32 8 0.83 2 5 8.27 5 3.83 7 0.64 2 M. vetusta Gosport 1 13.06 147 4.68 166 1.04 32 2 7.42 122 3.27 134 0.96 11 3 10.42 135 3.88 151 0.89 27 4 9.36 223 3.64 235 0.93 27 5 10.77 99 3.87 101 0.94 16 6 10.89 90 3.97 91 0.86 15 T. apita Gosport 1 3.53 1 1.56 1 - - 2 - - - - ■ ■ 3 14.57 1 6.15 2 - - 4 16.56 1 7.7 2 - . 5 20.4 3 7.87 3 - - 6 18.79 1 5.68 1 - - T. alveata Moodys (Chick. R.) 1 17.59 16 6.07 16 2.31 2 2 8.29 78 2.98 107 1.13 3 3 12 54 3.88 63 0.95 3 4 28.32 21 8.11 22 - - 5 27.93 16 8.22 16 2.01 2 T. alveata Moodys (LeFleurs) 1 25.09 2 7.56 2 - ■ 2 34.27 2 8.31 2 - ■ 3 28.01 1 6.95 1 0.5 1 T. alveata Moodys (Tcheva Ck.) 1 12.9 5 4.38 5 2.78 1 2 24.39 6 8.79 6 - - 3 6.62 2 2.79 2 ■ ■ 4 1.87 2 0.95 2 - - 5 16.08 5 4.95 6 - - 6 3.42 1 1.23 2 - - 7 25.39 17 8.16 19 1.71 1 8 17.2 16 6.22 21 1.63 2 9 22.96 17 7,62 23 1.08 3 U1 U1 Table 1: (continued) Taxon Formation (Outcrop) Sample # Mean Length Specim ens Mean WO Specim ens Diameter Specimens T. carinata Gosport 1 9.13 156 3.25 223 0.73 17 2 6.84 357 2.58 410 0.85 23 3 7.62 210 2.74 223 0.69 11 4 6.78 367 2.5 386 0.74 26 5 6.93 179 2.52 225 0.75 13 6 7.1 220 2.53 227 0.7 16 T. carinata Lisbon 1 5.06 12 1.98 22 0.57 1 2 6.81 278 2.15 353 0.63 42 T. fischeri Moodys (Tcheva Ck.) 1 22.9 1 6.51 1 - - 2 - - - - - - 3 - - - - - - 4 - - - - . - 5 7.85 1 6.66 4 . . 6 - - - • - - 7 - - - - - - 8 - - - - - - 9 - - - - - - T. ghigna Gosport 1 9.84 11 3.02 11 0.61 1 2 11.87 9 3.83 9 - - 3 10.69 8 3.82 8 1.48 2 4 11.41 10 4.26 11 1.42 2 5 8.86 5 3.45 5 0.48 1 6 16.66 1 4.81 1 - - T. houstonia Lisbon 1 - - - . . - 2 23.27 29 - - - - T. lisbonensis Lisbon 1 - - - - . - 2 14.36 18 - - - - T. mississippiensis Byram 1 4.91 123 1.78 181 0.49 25 2 10.09 75 3.4 113 0.61 8 3 9.57 103 2.91 116 1.3 2 4 7.65 69 2.63 102 0.43 5 5 7.5 111 2.64 151 0.56 13 6 10.11 141 3.45 217 0.59 7 7 9.08 139 3.42 219 0.54 6 8 8.53 135 2.98 187 0.63 4 9 9.7 79 2.9 93 0.4 7 tn CD Table 1 : (continued) Taxon Formation (Outcrop) Sample it Mean Length Specim ens Mean WD Specimens Diameter Specimens 10 8.09 113 2.6 162 0.32 5 11 8.59 80 2.77 112 0.56 9 12 7.44 120 2.47 155 0.73 7 T. nasuta Stone City 1 11.08 16 2.5 22 0.78 3 2 4.31 22 1.25 32 0.28 2 3 7.84 119 2.26 186 0.66 20 4 7.08 12 2.22 23 0.63 1 5 7.72 14 2.1 21 0.63 3 T. obruta Gosport 1 12.81 12 4.07 17 0.92 1 2 11.34 5 3.91 6 1.19 1 3 18.91 4 6.5 4 - - 4 13.94 8 4.53 8 1.47 1 5 12.26 2 4.03 2 - - 6 - - - - - - T. perdita Moodys (Chick. R.) 1 7.69 64 2.86 102 0.89 4 2 7.86 237 3.43 488 0.97 7 3 8.53 498 2.71 570 0.77 10 4 22.71 156 6.65 181 1.72 10 5 19.64 121 5.54 140 2.25 8 T. perdita Moodys (LeFleurs) 1 5.02 109 1.9 168 0.65 18 2 8.77 133 2.75 186 0.95 19 3 13.04 38 4.17 40 1.12 5 T. perdita Moodys (Tcheva Ck.) 1 5.58 301 1.76 335 0.59 43 2 10.34 32 3.33 36 0.64 1 3 5.51 269 2.02 320 0.72 17 4 5.7 155 2.11 201 0.74 14 5 6.4 160 2.22 201 0.61 12 6 5.12 19 1.88 28 0.58 3 7 11.37 148 3.64 171 0.76 9 8 8.3 73 2.6 87 0.81 7 9 11.25 92 3.52 99 0.88 6 Ol - Nl 58 taxa in whorl diam eter (p<0.05). Of th ese, highly significant variations are observed in o n e of the sam ples (p<0 .0 1 ) and very highly significant variations are observed in two of the sam ples (p<0.001). Average drillhole diam eter estim ates range from 0.64 mm to 1.31 mm for M. claibornensis (n=5) and from 0.28 mm to 0.78 mm for T. nasuta (n=5). M easured sam ple sizes range from 3 to 28 shells per two-liter sam ple (n=44). No significant variability is noted betw een taxa in any of the 5 sam ples. Moodvs Branch Formation Seventeen two-liter sam ples of th e Moodys Branch Formation w ere collected from three different outcrops, including T cheva Creek, LeFleur's Bluff, and the C hickasaw hay River in Mississippi (Figs. 11-13). Nine sam ples w ere collected from T cheva Creek, th ree sam ples w ere collected ffrom LeFleur's Bluff, and five sam ples w ere collected from the Chickasaw hay River. T he nine sam ples collected from T cheva C reek (Fig. 12) have three different sp ecies of turritelline gastropods, including T. alveata, T. fischeri, and T. perdita (Fig. 17d,f,k). Average length estim ates range from 1.87 mm to 25.39 mm for T. alveata (n=9), from 7.85 mm to 22.90 mm for T. fischeri (n=2), and from 5.12 mm to 11.25 mm for T. perdita (n=9; Table 1). M easured sam ple sizes range from 2 0 to 307 shells per two-liter sam ple (n=1322). C om parisons of shell length betw een th e se sp ecies sug g est that very highly significant differences exist in 6 of the 9 sam ples (p<0.001). A verage whorl diam eter estim ates range from 0.95 mm to 8.79 mm for T. alveata (n=9), 6.51 mm to 6 .6 6 mm for T. fischeri (n=2), and 1.76 mm to 3.64 mm for T. perdita (n=9). M easured sam ple sizes range from 30 to 341 shells per two-liter sam ple (n=1569). C om parisons of shell length betw een th ese sp ecies su g g est that very highly 59 significant differences exist in 6 of the 9 sam ples (pcO.001). Significant variability exists in the sam e sam ples which exhibit variability in length estim ates. Average drillhole diameter estim ates range from 0.50 mm to 2.78 mm for T. alveata (n=5) and from 0.59 mm to 0.88 mm for T. perdita (n=5). M easured sample sizes range from 2 to 44 shells per two-liter sample (n=74). Significant variability is observed in two of the 4 sam ples available for study (pxO.05; i.e., 5 of the 9 sam ples did not contain drilled shells or only had one drilled specimen available for study). The three two-liter sam ples collected from LeFleur's Bluff (Fig. 11) have two species of turritelline gastropods, including T. alveata and T. perdita (Fig. 17d,k). Average length estim ates range from 25.09 mm to 34.27 mm for T. alveata (n=3), and from 5.02 mm to 13.04 mm for T. perdita (n=3; Table 1). Measured sample sizes range from 39 to 135 shells per two-liter sample (n=285). Significant differences in average shell length exist between these species in all sam ples (p<0.05). Of these, two of the three sam ples exhibit very highly significant (p<0.001) differences. Average whorl diameter estim ates range from 6.95 mm to 8.31 mm for T. alveata (n=3), and 1.90 mm to 4.17 mm for T. perdita (n=3). Measured sample sizes range from 41 to 189 shells per two-liter sample (n=401). Two of the three sam ples exhibit very highly significant variability within sam ples (p<0.001). Only one species is characterized by drillholes in the study sam ples from LeFleur's Bluff-thus, variability in predator size (between species) was not assessed. The five two-liter sam ples collected from the Chickasawhay River (Fig. 13) have the sam e two species, T. alveata and T. perdita (Fig. 17d,k). Average length estim ates range from 8.29 mm o 28.32 mm for T. alveata (n=5), and from 60 7.69 mm to 22.71 mm for T. perdita (n=5; Table 1). M easured sam ple sizes range from 80 to 552 shells per two-liter sam ple (n=1261). Significant differences in av erag e shell length betw een sp ecies exist in 3 of the 5 sam ples (p<0.05). Of these, two sam ples exhibit very highly significant (p<0.001) differences. A verage whorl diam eter estim ates range from 2.98 mm to 8 .2 2 mm for T. alveata (n=5) and from 2.71 mm to 6.65 mm for T. perdita (n=5). M easured sam ple sizes range from 118 to 633 shells per two-liter sam ple (n=1705). Four of five sam ples exhibit significant variability within sam ples (p<0.05). Of these, one is highly significant (p<0.01) and two are very highly significant (p<0.001). A verage drillhole diam eter estim ates range from 0.95 mm to 2.31 mm for T. alveata (n=4), and from 0.77 mm to 2.25 mm for T. perdita (n=4). M easured sam ple sizes range from 6 to 13 shells per two-liter sam ple (n=39). Four of five sam ples from this outcrop contained drilled shells and were used in th e se an aly ses of variability. O ne of four sam ples exhibits significant variability in drillhole diam eter (p<0.05). Lisbon Formation Two two-liter sam ples of the Lisbon Formation w ere collected from an outcrop along th e Tom bigbee River (Fig. 7) and contain two sp ecies of turritelline gastropods, including M. claibornensis and T. carinata (Fig. 17a,e). A verage length estim ates range from 2.91 mm to 17.63 mm for M. claibornensis (n=2), and from 5.06 mm to 6.81 mm for T. carinata (n=2 ; Table 1). M easured sam ple sizes range from 14 to 365 shells per two-liter sam ple (n=379). Very highly significant variations exist in one of the two sam ples (p<0.001). This is the sa m e sam ple which contains the larger num ber of individuals and species. 61 A verage whorl diam eters range from 1.26 mm to 6.50 mm for M. claibornensis (n=2) and from 1.96 mm to 2.15 mm for 7. carinata (n=2). M easured sam ple sizes range from 24 to 457 shells per two-liter sam ple (n=481). 7. houstonia and 7. lisbonensis are only present in one of the two sam ples. Very highly significant variations exist in one of th e two sam ples (p<0.001). This is the sam e sam ple which contains the larger num ber of individuals and species. Average drillhole diam eter estim ates range from 0.71 mm to 1.28 mm for M. claibornensis (n=2), from 0.57 mm to 0.63 mm for 7. carinata (n=2), and are 1.04 mm and 1.11 mm for 7. lisbonensis (n=1) and 7. houstonia (n=1), respectively). Only o n e of the two-liter sam ples contains m ore than o n e drilled shell (n=75). Very highly significant variability exists in this sam ple (p<0.001). This is the sa m e sam ple which contains the larger num ber of individuals and species. Gosport Sand Six two-liter sam ples of the G osport Sand w ere collected from a locality at Little Stave Creek, A labam a (Fig. 9), and have five different species of turritelline gastropods, M. vetusta, 7. apita, 7. carinata, 7. ghigna, and 7. obruta (Fig. 17b,c,e,g). A verage length estim ates range from 7.42 mm to 13.06 mm for M. vetusta (n=6 ), from 3.53 mm to 14.57 mm for 7 apita (n=5), from 6.84 mm to 9.13 mm for 7. carinata (n=6 ), from 8 .8 6 mm to 16.66 mm for 7. ghigna (n=6), and from 1 1.34 mm to 18.91 mm for 7. obruta (n=5; Table 1). M easured sam ple sizes range from 286 to 610 shells per two-liter sam ple (n=2386). Very highly significant variability exists betw een sp ecies within all six sam p les (p<0 .0 0 1 ). Average whorl diam eter estim ates range from 3.27 mm to 4.68 mm for M. vetusta (n=6 ), from 1.56 mm to 7.87 mm for 7. apita (n=6 ), from 2.50 mm to 3.25 mm for 7. carinata (n=6 ), from 3.02 mm to 4.81 mm for 7. ghigna (n=6 ), and from 62 3.91 mm to 6.50 mm for T. obruta (n=5). M easured sam ple sizes range from 320 to 643 shells per two-liter sam ple (n=2666). Very highly significant variability exists betw een sp ecies within all six sam ples (p<0 .0 0 1 ). A verage drillhole diam eter estim ates range from 0.86 mm to 1.04 mm for M. vetusta (n=6), are 1.34 mm for T. apita (n=1), range from 0.69 mm to 0.85 mm for T. carinata (n=6 ), from 0.48 mm to 1.48 mm for T. ghigna (n=4), and from 0.92 mm to 1.47 mm for T. obruta (n-3). Drilled T. apita w ere only present in one sam ple and w ere thus not analyzed for variance. M easured sam ple sizes range from 31 to 56 shells per two-liter sam ple (n-244). Significant variability exists betw een species within two of the six sam ples (p<0.05). Of these, highly significant variability is observed in one sam ple (p<0 .0 1 ). Summary Significant variability betw een constituent tax a is observed in prey and predator size p aram eters at all of the outcrops for which d a ta w as available. Significant variability is observed in prey size p aram eters in 24 out of 30 sam ples w h ereas variability is only observed in predator size in 6 out of 2 0 sam p les (Table 2). Mixed Species: Betw een S am ples S am ples at six outcrops of the G osport (n=1), Lisbon (n=1), S tone City (n=1), and Moodys Branch (n=3) Form ations w ere com pared to one another to determ ine variability betw een two-liter sam ples (Figs. 1,3). A verage length estim ates range from 9.54 mm to 13.89 mm in G osport sam ples (n=6 ), from 3.98 mm to 15.52 mm in Lisbon sam ples (n=2), from 6.37 mm to 10.61 mm in S tone Formation Sam ple # Length Max WD BH Diam % Drill % Inelf. % Peel % Bkn % Epis G osport 1 0.000 0.000 0.090 0.070 0.150 0.030 0.030 0.000 2 0.000 0.000 0.310 0.560 0.940 0.040 0.020 0.000 3 0.000 0.000 0.010 0.020 0.130 0.080 0.020 0.004 4 0.000 0.000 0.050 0.250 0.290 0.130 0.160 0.430 5 0.000 0.000 0.190 0.005 0.006 0.640 0.000 0.110 6 0.000 0.000 0.210 0.220 0.600 0.830 0.730 0.008 Lisbon 1 0.410 0.230 - 0.030 - - 0.020 - 2 0.000 0.000 0.000 0.000 0.000 0.000 0.003 0.000 Moodys (Chick R.) 1 0.000 0.000 0.020 0.080 0.130 0.410 0.050 0.000 2 0.530 0.020 0.670 0.520 0.030 0.850 0.030 0.500 3 0.000 0.000 0.410 0.080 0.740 0.060 0.540 0.420 4 0.080 0,070 - 0.290 - 0.590 0.850 0.190 5 0.020 0.005 0.930 0.230 0.560 0.250 0.410 0.540 Moodys (LeFleurs) 1 0.000 0.000 . 0.630 0.810 0.720 0,310 0.000 2 0.000 0.000 - 0.650 0.690 0.001 0.830 0.850 3 0.040 0.150 - 0.710 - 0.040 0.410 0.880 Moodys (Tcheva) 1 0.000 0.000 0.680 0.810 0.960 0.001 0.820 0.920 2 0.000 0.000 - 0.150 - 0.110 0,880 0.570 3 0.630 0.250 - 0.760 0.890 0.030 0.260 0.710 4 0.120 0.120 - 0.750 0.810 0.740 0.050 0.680 5 0.000 0.000 ■ » 0.750 0,950 0.030 0.070 0.730 6 0.560 0.270 - 0.710 0.790 0.640 0.200 0.710 7 0.000 0.000 0.020 1.000 0.560 0.000 0.050 0.630 8 0.000 0.000 0.030 0.720 0.780 0.002 0.030 0.220 g 0.000 0.000 0.420 0.890 0.020 0.006 0.090 0.790 S to n e City 1 0.650 0.002 0.320 0.660 - 0.780 - 0.160 2 0.009 0.000 0.070 0.001 - 0.530 0.340 - 3 0.380 0.000 0.340 0.970 0.910 0.002 0.004 0.030 4 0.640 0.120 0.600 0.090 - 0.090 0.140 - 5 0.890 0.025 0.450 0.080 - 0.190 0.230 - T able 2: P-values for com parisons of tax a within sam ples. 64 City sam ples (n=5), from 8.08 mm to 25.79 mm in Moodys Branch sam ples from the C hickasaw hay River (n=5), from 15.05 mm to 21.52 mm in M oodys Branch sam p les from LeFleur's Bluff (n=3), and from 3.78 mm to 25.50 mm in Moodys Branch sam ples from T cheva Creek (n=9; Table 3). Significant variability is only observed in one of th ese six outcrops--at the outcrop of the Moodys Branch Form ation at th e C hickasaw hay River (p<0.05). Average whorl diam eter estim ates range from 3.91 mm to 4.56 mm in G osport sam ples (n=6), from 1.62 mm to 4.49 mm in Lisbon sam ples (n=2), from 2.96 mm to 3.85 mm in Stone City S am ples (n-5), from 3.20 mm to 7.38 mm in Moodys Branch sam ples from the C hickasaw hay River (n=5), from 4.73 mm to 5.56 mm in Moodys Branch sam p les from LeFleur's Bluff (n=3), and from 1.53 mm to 6.06 mm in Moodys Branch sam p les from T cheva C reek (n=9). Significant variability in whorl diam eters is not observed in any of th e se outcrops. A verage drillhole diam eter estim ates range from 0.78 mm to 1.14 mm in G osport sam ples (n=6), from 0.64 mm to 1.01 mm in Lisbon sam ples (n=2), from 0.73 to 1.00 mm in S tone City sam p les (n=5), from 0.86 mm to 2.13 mm in Moodys Branch sam ples from the C hickasaw hay River (n=4), and from 0.55 mm to 1.71 mm in Moodys Branch sam p les from T cheva C reek (n=5). Significant variability in drillhole diam eters is not observed in any of th ese 5 outcrops. Summary W hen utilizing m ixed-species sam ple m eans to analyze differences betw een sam ples, significant variability is observed in one of the six studied outcrops (Table 4). Significant variability is noted in prey length estim ates, but is not noted in estim ates of prey width or predator size. 65 Form ation (Outcrop) Sam ple # M ean Length # of Taxa M ean WD # of Taxa M ean BH Diam eter # of T axa G osport 1 11.21 4 4.29 5 0.82 4 2 10.41 5 3.95 5 1 3 3 12.84 5 3.95 5 1.02 3 4 13.89 5 4.56 5 1.14 4 5 11.52 5 3.91 5 0.88 4 6 9.54 4 3.22 4 0.78 2 Lisbon 1 3.98 2 1.62 2 0.64 2 2 15.52 4 4.49 4 1.01 4 M oodys (Chick. R.) 1 12.64 2 4.46 2 1.6 2 2 8.08 2 3.2 2 1.05 2 3 10.26 2 3.29 2 0.86 2 4 25.51 2 7.38 2 - - 5 23.79 2 6.88 2 2.13 2 Moodys (LeFiaurs) 1 15.05 2 4.73 2 - - 2 21.51 2 5.53 2 - - 3 20.53 2 5.56 2 - - Moodys (Tcheva Ck.) 1 13.79 3 4,21 3 0.55 2 2 17,36 2 6.06 2 1.71 2 3 6.07 2 2.4 2 ■ - 4 3.78 2 1.53 2 - - 5 10.11 3 4.61 3 - - 6 4.27 2 1.55 2 1.24 2 7 18.38 2 5.9 2 1.22 2 8 12.75 2 4.41 2 0.98 2 g 17.1 2 5.67 2 - - Stone City 1 8.26 2 3.85 2 1 2 2 10.09 2 3.5 2 1 2 3 10.61 2 3.41 2 0.72 2 1 4 6.37 2 3.41 2 0.73 2 1 5 6.37 2 2.96 2 0.73 2 T able 3: M ixed-species predator and prey size characteristics. M ean v alu es (in mm) used to analyze betw een-sam ple variability. Formation (Outcrop) Length Max WD BH Diam % Drill % Ineff, % Peel % Bkn. % Epis. Gosport 0.820 0.830 0.660 0.720 0.280 0.700 0.880 0.360 Lisbon 0.090 0.100 0.150 0.910 0.400 0.310 0.430 0.420 Moodys (Chick R.) 0.040 0.090 0.200 0.470 0.370 0.070 0,540 0.270 Moodys (LeFleurs) 0.900 0.960 - 0.980 0.550 0.520 0.470 0.480 Moodys (Tcheva) 0.290 0.410 0.690 0.520 0.300 0.450 0.360 0.001 Stone City 0.750 0.990 0.530 0.990 0.000 0.530 0.470 0.510 Table 4: M ixed-species p-values for com parisons of sam ples within outcrops. 67 Mixed Species: Between Outcrops Two-liter sam ples were collected at three outcrops of the Moodys Branch Formation at the Chickasawhay River, Tcheva Creek, and at LeFleur's Bluff in order to a s s e s s variability betw een different outcrops of the sam e formation (Figs. 11-13). Average length estim ates range from 11.51 mm to 19.03 mm (Table 5). Mean length estim ates for each outcrop are based on 9 sam ples at T cheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean shell length estim ates is not observed betw een th ese three outcrops. Average whorl diam eter estim ates range from 4.03 mm to 5.27 mm. Mean whorl diam eter estim ates for each outcrop are based on 9 sam ples at T cheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean whorl diam eter estim ates is not observed betw een th ese three outcrops. Average drillhole diam eter estim ates range from 1.14 mm to 1.41 mm. Mean whorl diam eter estim ates for the two available outcrops are based on 5 sam ples at Tcheva Creek and 4 at the Chickasawhay River. Significant variability in m ean drillhole diam eter is not observed betw een th ese two outcrops. Summary When utilizing m ixed-species sam ple m eans to analyze differences betw een outcrops, significant variability is not observed in any of the studied param eters. Results are sum m arized in Table 6. 68 # of Samples to n O l < 5 O' 2 I 16.00% 128.00% 8 a Mean % # of Broken i Sam ples LO 8 Pi C O & 8 o> 89.00% I 9 # of .Samples \ n to O ) M ean % Peel 14.00% I 39.00% I 25.00% f f of Samples tn C O O ) | M ean % | Inetf. [ 1.0 0 % I 1 .0 0 % I 2.00% f t of Samples in co O i M ean % D rill I %00‘S l %00’S | I 5.00% i f of Samples • i n Mean BH Diameter • I 1.14 I # of Samples i n CO O ) Mean WD SI a 15.62 36.25 f t of Samples m CO o Mean Length t o o <0 o o> in Outcrop < D > i t > nj i i u O |L e Fleurs B luff | iTcheva Creek I Table 5: Mixed species values for all studied param eters. Mean values and num ber of sam ples used to analyze between-outcrop variability. Size param eters are in mm. 69 Formation Length Max WD BH Diam % Drill % Ineff. % Peel % Bkn. % Epis. Moodys Branch 1 0.180 0.440 I 0.440 0.960 0.590 0.160 0.420 0.040 Table 6: Mixed-species p-values for comparisons of outcrops within the sam e formation. 70 Mixed Species: Between Formations Four formations from the sam e epoch were compared to one another in order to a sse ss variability between them. T hese included the Gosport, Lisbon, Moodys Branch, and Stone City Formations (Fig. 3). Average length estim ates for each formation range from 8.34 mm to 14.18 mm (n-4; Table 7). Mean length estim ates are based on 6 sam ples in the Gosport Sand, 2 sam ples in the Lisbon Formation, 17 sam ples in the Moodys Branch Formation, and 5 samples in the Stone City Beds. Significant variability in m ean shell length is not observed between these formations. Average whorl diameter estim ates for each formation range from 3.06 mm to 4.55 mm (n=4). Mean whorl diameter estim ates are based on 6 sam ples in the Gosport Sand, 2 sam ples in the Lisbon Formation, 17 sam ples in the Moodys Branch Formation, and 5 samples in the Stone City Beds. Significant variability in mean whorl diameter is not observed between these formations. Average drillhole diameter estim ates for each formation range from 0.83 mm to 1.26 mm (n=4). Mean drillhole diameter estim ates are based on 6 sam ples from the Gosport Sand, 2 sam ples from the Lisbon Formation, 9 sam ples from the Moodys Branch Formation, and 5 sam ples from the Stone City Beds. Significant variability in m ean drillhole diam eter is not observed between these formations. Summary When utilizing mixed-species sample m eans to analyze differences between outcrops, significant variability is not observed in any of the studied formations. Results are summarized in Table 8. # o f S am ples C O C v J in 5^ £ 'o. S L U s I 26.00% | | % 00’S | I 16.00% I 2.00% j Mean % # of I B kn Sam ples t o & 8 3 158.00% I 2 1 177.00% ! 1 7 I 186.00% ( 5 I u i a> ° c * § % to O J r-. in it of j Mean % Samples P eel -a f <0 r 2 1 11.00 % I 1 7 1 24.00% I 5 I 17.00% Mean % Inef. 1 2.00% | l 5.00% I 1 1.00% I 1.00% I : # of S am ples < 0 O J in Mean % Drill * • 2 ° 8 I 26.00% I I %oo s l I 15.00% I # o f S am ples CD O J w O ) Mean BH D iam eter 1 0.94 I I 0.83 I ___0.83 I 1.26 # o f S am ples CD CM N tn M ean WD 1 86'e 1 I 3.06 I 4.55 | CM ^r C O # of S am ples C O CM N m M ean Length f". t n I 9 1 6 I 14.18 | ! 8.34 | Form ation iGosport I iLisbon I I Moodys Branch I I Stone C itv I Table 7: Mixed-species values for all studied param eters. Mean values and number of sam ples used to analyze between-formation variability. Size param eters are in mm. 72 Scale Length Max WD BH Diam % Drill % Ineff. % Peel % Bkn. % Epis. Between Formation 0.190 0.290 0.120 0.000 0.170 0.260 0.000 0.010 Table 8: Mixed-species p-values for com parisons of formations of similar age. 73 Within Species: Between Sam ples Eleven species of turritelline gastropods were examined from 7 outcrops of 5 different formations in order to a sse ss within-species patterns of variability in predator and prey size characteristics. T hese taxa include M.esalia claibornensis, M. vetusta, Turritella apita, T. alveata, T. carinata, T. fischeri, T. ghigna, T. mississippiensis, T. nasuta, T. obruta, and T. perdita (Fig. 17). Mesalia claibornensis Seven sam ples of M. claibornensis (Fig. 17a) were collected from outcrops of the Stone City Beds along the Brazos River and from the Lisbon Formation along the Tombigbee River (Figs. 5, 7). Average length estim ates for each sam ple from the Lisbon Formation range from 2.91 mm to 17.63 mm (n=2; Table 1). M easured shell abundances range from 2 to 50 specim ens per two- liter sam ple (n=52). Highly significant variability in length is observed between th ese sam ples (p<0.01). Average whorl diam eter estim ates for each sam ple range from 1.26 mm to 6.50 mm (n=2 ). M easured shell abundances range from 2 to 53 specim ens per two-liter sam ple (n=55). Very highly significant variability in whorl diam eter is observed between these sam ples (p<0.001). Average drillhole diam eter estim ates for each sample range from 0.71 mm to 1.28 mm (n=2 ). M easured shell abundances range from 1 to 25 specim ens per two-liter sam ple (n-26). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Average length estim ates for each sam ple from the Stone City Beds range from 5.66 mm to 16.91 mm (n=5; Table 1). M easured shell abundances range from 2 to 43 specim ens per two-liter sam ple (n=62). Significant variability in length is not observed between these sam ples. Average whorl diam eter 74 estim ates for each sam ple range from 3.32 mm to 5.74 mm (n=5). M easured shell abundances range from 3 to 81 specim ens per two-liter sam ple (n=109). Significant variability in whorl diam eter is not observed betw een th ese sam ples. Average drillhole diam eter estim ates for each sam ple range from 0.64 mm to 1.31 mm (n=5). M easured shell abundances range from 1 to 8 specim ens per two-liter sam ple (n=15). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Mesalia vetusta Six sam ples of M.vetusta (Fig. 17b) w ere collected from an outcrop of the Gosport Sand at Little Stave Creek, Alabama (Fig. 9). Average length estim ates for each sam ple range from 7.42 mm to 13.06 mm (n=6 ; Table 1). M easured shell abundances range from 90 to 223 specim ens per two-liter sam ple (n=816). Very highly significant variability in length is observed betw een th ese sam ples (p<0.001). Average whorl diam eter estim ates for each sam ple range from 3.27 mm to 4.68 mm (n=6 ). M easured shell abundances range from 91 to 235 specim ens per two-liter sam ple (n=878). Very highly significant variability in whorl diam eter is observed betw een th e se sam ples (p<0 .0 0 1 ). Average drillhole diam eter estim ates for each sam ple range from 0.86 mm to 1.04 mm (n=6 ). M easured shell abundances range from 11 to 32 specim ens per two-liter sam ple (n=128). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Turritella aoita Six sam ples of T. apita (Fig. 17c) w ere collected from an outcrop of the Gosport Sand at Little Stave Creek, Alabam a (Fig. 9). Average length estim ates for each sam ple range from 3.53 mm to 20.40 mm (n=5; Table 1). M easured 75 shell ab u n d an ces range from 1 to 3 specim ens per sam ple (n=7). Average whorl diam eter estim ates for each sam ple range from 1.56 mm to 7.87 mm (n=5). M easured shell abundances range from 1 to 3 specim ens per two-liter sam ple (n=9). Lack of multiple shells in th ese sam p les m akes analysis of variance u n n ecessary in th e se param eters. Turritella alveata S eventeen sam ples of 7. alveata (Fig. 17d) were collected from 3 outcrops of th e M oodys Branch Formation at outcrops at th e Chickasaw hay River, LeFleur's Bluff, and T cheva C reek in Mississippi (Figs. 11-13). Average length estim ates for each sam ple from th e C hickasaw hay River outcrop range from 8.29 mm to 28.32 mm (n=5; Table 1). M easured shell ab u n d an ces range from 16 to 78 specim ens per two-liter sam ple (n=185). Very highly significant variability in length estim ates is observed betw een th e se sam p les (p<0 .0 0 1 ). A verage whorl diam eter estim ates for each sam ple range from 2.98 mm to 8.11 mm (n=5). M easured shell abundances range from 16 to 107 specim ens per two-liter sam ple (n=224). Very highly significant variability in whorl diam eter estim ates is observed betw een th e se sam ples (p<0.001). Average drillhole diam eter estim ates for each sam ple range from 0.95 mm to 2.31 mm (n=4). M easured shell ab u n d an ces range from 2 to 3 specim ens per two-liter sam ple (n=10). Significant variability in drillhole diam eter is not observed betw een th e se sam ples. A verage length estim ates for each sam ple from LeFleur's Bluff range from 25.09 mm to 34.27 mm (n -3 ; Table 1). M easured shell ab u n d an ces range from 1 to 2 specim ens per two-liter sam ple (n=5). Significant variability in length is not observed betw een th e se sam ples. Average whorl diam eter 76 estim ates for each sam ple range from 6.95 mm to 8.31 mm (n=:3). M easured shell a b u n d an ces range from 1 to 2 specim ens per two-liter sam ple (n=5). Significant variability in whorl diam eter is not observed betw een th e se sam ples. A verage drillhole diam eter estim ates w ere not calculated b e ca u se th ere w ere no drilled shells in the studied sam ples from LeFleur’s Bluff. A verage length estim ates for each sam ple from T cheva C reek range from 1.87 mm to 25.39 mm (n=9; Table 1). M easured shell ab u n d an ces range from 1 to 17 specim ens per two-liter sam ple (n-71). Very highly significant variability in length is observed betw een th ese sam ples (p<0 .0 0 1 ). A verage whorl diam eter estim ates for each sam ple range from 0.95 mm to 8.79 mm (n=9). M easured shell a b u n d an ces range from 2 to 23 specim ens per two-liter sam ple (n=8 6 ). Very highly significant variability in whorl diam eter is observed betw een th ese sam p les (p<0.001). A verage drillhole diam eter estim ates for each sam ple range from 0.50 mm to 2.78 mm (n=5). M easured shell ab u n d an ces range from 1 to 3 specim ens per two-liter sam ple (n=8 ). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Turritella carinata Eight sam ples of 7 " . carinata (Fig. 17e) w ere collected from the G osport and Lisbon Form ations at Little Stave C reek and th e T om bigbee River, respectively (Figs. 7, 9). A verage length estim ates for each sam ple from the G osport range from 6.78 mm to 9.13 mm (n=6 ; Table 1). M easured shell ab u n d an ces range from 156 to 367 specim ens per two-liter sam ple (n=1489). Very highly significant variability in length is observed betw een th e se sam ples (p<0.001). A verage whorl diam eter estim ates for each sam ple range from 2.50 mm to 3.25 mm (n=6 ). M easured shell ab u n d an ces range from 223 to 410 77 specim ens per two-liter sam ple (n=1694). Very highly significant variability in whorl diam eter is observed betw een these sam ples (p<0.001). Average drillhole diam eter estim ates for each sam ple range from 0.69 mm to 0.85 mm (n=6 ). M easured shell abundances range from 11 to 26 specim ens per two-liter sam ple (n=106). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Average length estim ates for each sam ple from the Lisbon range from 5.05 mm to 6.81 mm (n=2 ; Table 1). M easured shell abundances range from 12 to 278 specim ens per two-liter sam ple (n=290). Significant variability in length is not observed betw een th ese sam ples. Average whorl diam eter estim ates for each sam ple range from 1.98 mm to 2.15 mm (n=2). M easured shell abundances range from 22 to 353 specim ens per two-liter sam ple (n=375). Significant variability in whorl diam eter is not observed betw een th ese sam ples. Average drillhole diam eter estim ates for each sam ple range from 0.57 mm to 0.63 mm (n-2). M easured shell abundances range from 1 to 42 specim ens per two-liter sam ple (n=43). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Turritella fischeri Two sam ples of T. fischeri (Fig. 17f) w ere collected from the Moodys Branch Formation at T cheva Creek (Fig. 12). Lack of suitable shells for length estim ates and lack of drilled shells m akes analysis of variance in shell length and drillhole diam eter impossible. Average whorl diam eter estim ates for each sam ple range from 6.51 mm to 6.6 6 mm (n=2 ; Table 1). M easured shell abundances range from 1 to 4 specim ens per two-liter sam ple (n=5). Significant variability in whorl diam eter is not observed betw een th ese sam ples. 78 Turritella ahiana Six sam ples of T. ghigna (Fig. 17g) were collected from the Gosport Sand at Little Stave Creek, Alabama (Fig. 9). Average length estim ates for each sam ple range from 8.8 6 mm to 16.66 mm (n=6 ; Table 1). M easured shell abundances range from 1 to 11 specim ens per two-liter sam ple (n-44). Significant variability in length is not observed betw een th ese sam ples. Average whorl diam eter estim ates for each sam ple range from 3.20 mm to 4.81 mm (n=6 ). M easured shell abundances range from 1 to 11 specim ens per two- liter sam ple (n=45). Significant variability in whorl diam eter is not observed betw een th ese sam ples. Average drillhole diam eter estim ates for each sam ple range from 0.48 mm to 1.42 mm (n=4). M easured shell abundances range from 1 to 2 specim ens per two-liter sam ple (n=6 ). Lack of multiple specim ens in som e sam ples prevents analysis of variability in drillhole diam eter betw een th ese sam ples. Turritella mississiopiensis Twelve sam ples of T. mississippiensis (Fig. 17h) were collected from the Byram Formation at W est Talahalla Creek in Mississippi (Fig. 15). Average length estim ates for each sam ple range from 4.91 mm to 10.11 mm (n=12; Table 1). M easured shell abundances range from 69 to 141 specim ens per two- liter sam ple (n=1 2 ). Very highly significant variability in length is observed betw een th ese sam ples (p<0.001). Average whorl diam eter estim ates for each sam ple range from 1.78 mm to 3.45 mm (n=12). M easured shell abundances range from 93 to 219 specim ens per two-iiter sam ple (n=1808). Very highly significant variability in whorl diam eter is observed betw een th ese sam ples (p<0.001). Average drillhole diam eter estim ates for each sam ple range from 79 0.32 mm to 1.30 mm (n=12). M easured shell abundances range from 2 to 25 specim ens per two-liter sam ple (n=98). Highly significant variability in drillhole diam eter is observed betw een th ese sam ples (p<0 .0 1 ). Turritella nasuta Five sam ples of T. nasuta (Fig. 17i) w ere collected from the Stone City Beds at the Brazos River, T exas (Fig. 5). Average shell length estim ates for each sam ple range from 4.31 mm to 11.08 mm (n=5; Table 1). M easured shell abundances range from 12 to 119 specim ens per two-liter sam ple (n=183). Significant variability in length is observed betw een th ese sam ples (p<0.05). Average whorl diam eter estim ates for each sam ple range from 1.25 mm to 2.50 mm (n=5). M easured shell abundances range from 21 to 186 specim ens per two-liter sam ple (n=284). Very highly significant variability in whorl diam eter is observed betw een th ese sam ples (p<0.001). Average drillhole diam eter estim ates for each sam ple range from 0.28 mm to 0.78 mm (n=5). M easured shell abun dances range from 1 to 20 specim ens per two-liter sam ple (n=29). Significant variability in drillhole diam eter is not observed betw een th ese sam ples. Turritella obruta Five sam ples of T. obruta (Fig. 17]) w ere collected from the Gosport Sand at Little Stave Creek, Alabama (Fig. 9). Average shell length estim ates for each sam ple range from 11.34 mm to 18.91 mm (n=5). M easured shell abundances range from 2 to 12 specim ens per two-liter sam ple (n=31). Significant variability in length is not observed between th ese sam ples. Average whorl diam eter estim ates for each sam ple range from 3.91 mm to 6.50 mm (n=5). M easured 80 shell abundances range from 2 to 17 specim ens per two-liter sam ple (n=37). Significant variability in whorl diam eter is not observed between these sam ples. Variability in drillhole diam eter is not a sse ssed because no sam ples contain m ore than one drilled shell. Turritella oerdita Seventeen sam ples of T. perdita (Fig. 17k) were collected from 3 outcrops of the Moodys Branch Formation at outcrops at the Chickasawhay River, LeFleur's Bluff, and Tcheva Creek in Mississippi (Figs. 11-13). Average shell length estim ates for each sam ple from the Chickasawhay River range from 7.69 mm to 22.71 mm (n=5; Table 1). M easured shell abundances range from 64 to 498 specim ens per two-liter sam ple (n=1076). Very highly significant variability in length is observed between these sam ples (p<0.001). Average whorl diam eter estim ates for each sam ple range from 2.71 mm to 6.65 mm (n=5). Measured shell abundances range from 102 to 570 specim ens per two-liter sam ple (n=1481). Very highly significant variability in whorl diam eter is observed between these sam ples (p<0.001). Average drillhole diam eter estim ates for each sam ple range from 0.76 mm to 2.25 mm (n=5). M easured shell abundances range from 4 to 10 specim ens per two-liter sam ple (n=39). Significant variability in drillhole diam eter is not observed betw een these sam ples. Average shell length estim ates for each sam ple from LeFleur's Bluff range from 5.02 mm to 13.04 mm (n=3; Table 1). M easured shell abundances range from 38 to 133 specim ens per two-liter sam ple (n=280). Very highly significant variability in length is observed between these sam ples (p<0 .0 0 1 ). 81 Average whorl diam eter estim ates for each sam ple range from 1.90 mm to 4.17 mm (n=3). M easured shell abundances range from 40 to 186 specim ens per two-liter sam ple (n=394). Very highly significant variability in whorl diam eter is observed between these sam ples {p<0.001). Average drillhole diam eter estim ates for each sam ple range from 0.65 mm to 1.12 mm (n=3). Measured shell abundances range from 5 to 19 specim ens per two-liter sam ple (n=42). Significant variability in drillhole diam eter is observed betw een these sam ples (p<0.05). Average shell length estim ates for each sam ple from Tcheva Creek range from 5.12 mm to 11.25 mm (n=9; Table 1). M easured shell abundances range from 19 to 301 per two-liter sam ple (n=1249). Very highly significant variability in length is observed between these sam ples (p<0.001). Average whorl diam eter estim ates for each sam ple range from 1.76 mm to 3.64 mm (n=9). M easured shell abundances range from 28 to 335 specim ens per two- liter sam ple (n=1478). Very highly significant variability in whorl diam eter is observed between these sam ples (p<0.001). Average drillhole diam eter estim ates for each sam ple range from 0.58 mm to 0.88 mm (n=9). Measured shell abundances range from 1 to 43 specim ens per two-liter sam ple (n=112). Significant variability in drillhole diam eter is not observed between these sam ples. Summary Utilizing individual taxa, significant differences were noted between sam ples in both prey size param eters and in the predator size param eter (Table 9). Analysis of prey length reveals significant variability between sam ples in 10 Table 9: Within-species p-values for comparisons o f samples within outcrops. Taxon Formation (Outcrop) Length Max WD BH Diam % D rill % Ineff. % Peel % Bkn. % Epis. M. claibornensis Lisbon 0.001 0.000 0.340 0.690 0.510 0.270 0.510 0.040 M. claibornensis Stone City 0.320 0.450 0.330 0.470 0.990 0.510 0.950 0.210 M. vetusta Gosport 0.000 0.000 0.790 0.260 0.040 0.050 0.610 0.000 T. apita Gosport - - - - - - 0.760 0.800 T. alveata Moodys (Chick. R.) 0.000 0.000 0.070 0.160 0.190 0.060 0.002 0.170 T. alveata Moodys (LeFleurs) 0.550 0.860 - - - - 0.630 0.630 T. alveata Moodys (Tcheva Ck.) 0.000 0.000 0.180 0.870 0.890 0.860 0.250 0.010 T. carinata Gosport 0.000 0.000 0.460 0.910 0.460 0.510 0.000 0.000 T. carinata Lisbon 0.070 0.410 0.790 0.290 0.720 0.320 - 0.290 T. fischeri Moodys (Tcheva Ck.) - 0.960 - - - 0.690 0.690 - T. ghigna Gosport 0.700 0.400 - 0.580 0.150 0.840 0.030 0.180 T. mississippiensis Byram 0.000 0.000 0.005 0.000 0.140 0.050 0.000 0.007 T. nasuta Stone City 0.020 0.000 0.400 0.210 0.900 0.810 0.000 0.002 T. obruta Gosport 0.620 0.120 - 0.930 - 0.610 0.970 0.860 T. perdita Moodys (Chick. R.) 0.000 0.000 0.360 0.030 0.001 0.000 0.000 0.000 T. perdita Moodys (LeFleurs) 0.000 0.000 0.040 0.890 0.290 0.020 0.510 0.340 T. perdita Moodys (Tcheva Ck.) 0.000 0.000 0.060 0.009 0.530 0.000 0.000 0.000 83 out of 15 taxa. Similarly, significant variability in prey width and predator size is observed in 10 out of 16 and 2 out of 12 taxa, respectively. Within Species: Between Outcrops Seventeen two-liter sam ples w ere collected at three outcrops of the Moodys Branch Formation at the Chickasawhay River, T cheva Creek, and at LeFleur's Bluff in order to a s s e s s variability betw een different outcrops of the sam e formation (Figs. 11 -13). T hese outcrops have two sp ecies of turritelline gastropods which are com m on to b o th - Turritella alveata and Turritella perdita (Fig. 17d,k). A verage shell length estim ates for T. alveata range from 14.54 mm to 29.12 mm (Table 10). Mean length estim ates for each outcrop are b ased on 9 sam ples at T cheva Creek, 5 at th e Chickasaw hay River, and 3 at LeFleur's Bluff. Significant variability in m ean shell length is not observed betw een th ese three outcrops (Table 11). Average whorl diam eter estim ates range from 5.01 mm to 7.61 mm. Mean whorl diam eter estim ates for each outcrop a re b ased on 9 sam ples at T cheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean whorl diam eter is not observed betw een th ese three outcrops. A verage drillhole diam eter estim ates range from 1.54 mm to 1.60 mm. Mean drillhole diam eter estim ates are based on 5 sam ples at Tcheva C reek and 4 sam ples at the Chickasaw hay River. Significant variability in m ean drillhole diam eter is not observed betw een th ese two outcrops. Average shell length estim ates for T. perdita range from 7.73 mm to 13.29 mm (Table 10). Mean length estim ates for each outcrop are b ased on 9 sam ples at T cheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. 84 I #of % Epis. [sam ples I 14.00% ! 5 I C O v fl 0s o o n! I 24.00% i 9 [ m v O O'* o o C O 0s* O O O T T I 29.00% I 9 I # o f sam p les W C O 0) in C O 05 % Bkn. I 69.00% I * * 5 o '* 8 8 I 93.00% I I 75.00% 98.00% I 88.00% I # o f sam p les tn C O C T ) in C O 05 © © a. O '* £ s O J [67.00% l kO o' S 8 16.00% l 13.00% ! 13.00% | #o! I samples! tn C O 0 > in C O 05 % IneH. I 1.00% I 0.00% I 6.00% | 1.00% I | 1.00% 1 I 2.00% # of sam p les tn C O o> to C O o> % Drill I 7.00% I 0.00% | 6.00% | 3.00% j 111.00% | I 6.00% # o f sam p les tn 4 0) in C O 0) s | o in C O 0 5 Length I 18.82 CM 05 CM [ 14.54 j 0) C J CO 0 5 c d I 7.73 I O utcrop if o !c O I LeFleurs I o < n > © xz j2 [f o .c O f2 3 © U - 5 iTcheva CkJ Taxon j T . a l v e a t a \ ■ Q t C D Q . Table 10: W ithin-species values for all studied param eters. Mean values and num ber of sam ples used to analyze betw een-outcrop variability. Size param eters are in mm. 85 ! % Epis. I S O 'O I e o o % Bkn. 0 .7 8 ! 0.00 % Peel 900 0.77 % Ineff. 0.27 0.27 % D rill 0.37 I 0.00 B H Diam 0.91 I 0.03 M a x WD i 0.34 0 .0 7 | Length 0.07 0.1 3 | Taxon ■ S to J " c o T . perdita Table 11: Within-species p-values for com parisons of outcrops within formations. 86 Significant variability in m ean shell length is not observed betw een th e s e three outcrops (Table 11). A verage whorl diam eter estim ates range from 2.56 mm to 4.24 mm. M ean whorl diam eter estim ates for each outcrop are b ased on 9 sam p les at T cheva C reek, 5 at the C hickasaw hay River, and 3 at LeFleur's Bluff. Significant variability in m ean whorl diam eter is not observed betw een th e se th ree outcrops. A verage drillhole diam eter estim ates range from 0.70 mm to 1.32 mm. M ean drillhole diam eter estim ates for each outcrop are b a se d on 9 sam p les at T cheva C reek, 5 at th e C hickasaw hay River, and 3 at LeFleur's Bluff. Significant variability in drillhole diam eter is observed betw een th e s e th ree outcrops (p<0,05). Summary Using individual taxa to a s s e s s variability, significant variability betw een outcrops of the sa m e formation is observed in one out of two taxa (Table 2). Significant variability betw een outcrops is only observed in predator size p a ram eters. Within S pecies: B etw een Form ations Four form ations from th e sa m e epoch w ere com pared to one another in order to a s s e s s variability betw een them . T h ese included th e Gosport, Lisbon, M oodys Branch, and S tone City Form ations (Fig. 3). Turritelline gastropod taxa which a re com m on to m ore than one of the studied form ations include Mesalia claibornensis and Turritella carinata (Fig. 17a,e). M. claibornensis occurs in the S tone City and Lisbon Form ations w hereas T. carinata occurs in the G osport and Lisbon Form ations. Average shell length estim ates for M. claibornensis range from 9.72 mm to 10.27 mm (Table 12). M ean length estim ates for each formation are b ased on 5 sam ples in the Stone City Beds and 2 sam ples in the Lisbon Formation. Significant variability in m ean shell length is not observed betw een th e se 2 formations. A verage whorl diam eter estim ates range from 3.86 mm to 4.53 mm. Mean whorl diam eter estim ates for each formation are b ased on 5 sam ples in the S tone City B eds and 2 sam ples in the Lisbon Formation. Significant variability in m ean whorl diam eter is not observed betw een th e se 2 formations. A verage drillhole diam eter estim ates range from 0.96 mm to 0.97 mm. M ean drillhole diam eter estim ates for each formation are b ased on 5 sam ples in the Stone City B eds and 2 sam ples in the Lisbon Formation. Significant variability in m ean drillhole diam eter is not observed betw een th e se 2 formations. Average shell length estim ates for T. carinata range from 5.93 mm to 7.40 mm (Table 12). Mean length estim ates for each formation are based on 6 sam ples in the G osport Sand and 2 sam ples in the Lisbon Formation. Significant variability in m ean shell length is not observed betw een th e se 2 formations. Average whorl diam eter estim ates range from 2.06 mm to 2.68 mm. Mean whorl diam eter estim ates for each formation are b ased on 6 sam ples in the G osport Sand and 2 sam ples in the Lisbon Formation. Significant variability in m ean whorl diam eter is observed betw een th ese 2 form ations (p<0.05). Average drillhole diam eter estim ates range from 0.60 mm to 0.74 mm. M ean drillhole diam eter estim ates for each formation are b ased on 6 sam ples in the G osport Sand and 2 sam ples in the Lisbon Formation. Significant variability in m ean drillhole diam eter is observed betw een th ese 2 form ations (p<0.05). t t of samples C M tn C D C M % Epis. ! 6 5 .0 0 % | & Q o CO ii.oo%| 0.00% 1 # of sam ples C M in C O C M # o f | samples % Bkn. O o V* o> s e o o o o 29.00% t 8 1 .0 0 % c m i n CO C M % Peel 2 0 .0 0 % 2 1 .0 0 % | 7.00% 3.00% I # o f sam ples C M t n CO C M % Ineff. 9.00% I 0.00% I * ' ■ 9 O ' O © 0.00% I M O Q . § O J C M m C O C M t t o f I samples] % Drill O o C O C M o'* o © w in S ' © o C D CO & o o cd C M x 1 m g o> 07 O to 03 d 0.74 o.eol t t of sam ples C M tn C D C M Max WD 00 C O C 9 C O in ** 8 C M 2 .0 6 t t of sam ples C M in C D C M Length N C M O C M N o> © h - 5.93 I c 15 § _£ c o X p \M . c l a i b o r n e n s i s [Lisbon I > o o e o w | T. c a r in a ta [Gosport | e 0 n tn l_l Table 12: W ithin-species values for all studied param eters. Mean values and num ber of sam ples used to analyze betw een- formation variability. Size param eters are in mm. 89 Summary Using individual taxa to a sse ss variability between formations of similar age, significant variability is observed in one of two taxa (Table 13). Significant variability is observed in prey width and predator size param eters. Predation Characteristics Between Species: Within Sam ples Stone Citv Beds Five two-liter sam ples of the Stone City Beds were collected from an outcrop along the Brazos River in Texas (Fig. 5) and contain two species of turritelline gastropods, M. claibornensis and T. nasuta (Figs. 17a,i). Average drilling intensity estim ates range from 11% to 33% for M. claibornensis (n=5) and from 0 % to 14% for T. nasuta (n=5; Table 14). M easured sam ple sizes range from 28 to 267 shells per two-liter sam ple (n=393). Comparisons of drilling intensity between these species (within each sample) suggest that very highly significant variability exists in one of the 5 sam ples (p<0.001). Average drilling inefficiency estim ates range from 0 % to 1 % for M. claibornensis (n=5) and from 0% to 1% for T. nasuta (n=5). Measured sam ple sizes range from 28 to 267 shells per two-liter sam ple (n=393). Significant variations in drilling inefficiency are not observed in these sam ples. Average peeling intensity estim ates range from 0% to 43% for M. claibornensis (n=5) and from 4% to 14% for T. nasuta (n=5). Measured sam ple sizes range from 28 to 267 shells per two-liter sample (n=393). Highly significant variability in peeling intensity is observed in 1 of the 5 sam ples (p<0.01). 90 Taxon Length WD BH Diam % Drill % Ineff. % Peel % Bkn. % Epis. M. claibornensis 0.920 0.700 0.890 0.050 0.130 0.920 0.080 0.140 T. cannata 0.110 0.030 0.020 0.260 0.090 0.060 0.000 0.080 T able 13: W ithin-species p-values for com parison of betw een-form ation variability. 91 Taxon Form ation (Outcrop) Sam ple # If of I M ean % Specim ens Drill M ean % Ineff. M ean % Peel M ean % Bkn M ean % Epis M. claibornensis Lisbon 1 53 35.85% 18.87% 39.62% 69.00% 18.87% 2 2 I 50.00% 0.00% 0.00% 0.00% 0.00% M. claibornensis Stone City 1 10 20.00% 0.00% 10.00% 100.00% 0.00% 2 3 33.33% 0.00% 0.00% 100.00% 0.00% 3 61 11.11% 1.23% 29.63% 84.00% 2.47% 4 8 25.00% 0.00% 25.00% 62.00% 0.00% 5 7 28.57% 0.00% 42.86% 71.00% 0.00% M. vetusta Gosport 1 151 13.91% 6.62% 4,64% 28.00% 19.28% 2 166 16.67% 5.42% 14.46% 15.00% 18.66% 3 134 8.21% 0.75% 5.97% 15.00% 18.66% 4 235 9.79% 2.98% 6.81% 22.00% 17.45% 5 101 12.87% 8.91% 9.90% 11.00% 19.80% 6 91 13.19% 4.40% 9.89% 34.00% 10.99% T. apita Gosport 1 1 0.00% 0.00% 0.00% 0.00% 0.00% 2 1 100.00% 0.00% 0.00% 0.00% 0.00% 3 3 0.00% 0.00% 0.00% 33.00% 33.33% 4 2 0.00% 0.00% 0.00% 0.00% 0.00% 5 3 0.00% 0.00% 0.00% 0.00% 0.00% 6 2 0.00% 0.00% 0.00% 0.00% 50.00% T. aiveata Moodys (Chick R.) 1 16 12.50% 6.25% 6.25% 100.00% 50.00% 2 107 2.80% 0.93% 4.67% 86.00% 17.76% 3 63 4.76% 0.00% 14.29% 76.00% 12.70% 4 22 0.00% 0.00% 22.73% 82.00% 36.36% 5 16 12.50% 0,00% 12.50% 87.00% 37.50% T. aiveata Moodys (LeFleurs) 1 2 0.00% 0.00% 0.00% 100.00% 50.00% 2 2 0.00% 0.00% 100.00% 50.00% 0.00% 3 1 0.00% 0.00% 100.00% 100.00% 0.00% T. aiveata Moodys (T cheva Ck.) 1 5 20.00% 0.00% 40.00% 100.00% 0.00% 2 6 16.67% 0.00% 50.00% 100.00% 0.00% 3 2 0.00% 0.00% 50.00% 100.00% 0.00% 4 2 0.00% 0.00% 0.00% 100.00% 0.00% 5 6 0.00% 0.00% 33.33% 83.00% 16.67% 6 2 0.00% 0.00% 0.00% 100.00% 0.00% 7 19 5.26% 0.00% 57.89% 89.00% 10.53% 8 21 4.76% 4.76% 42,86% 95.00% 4.76% 9 23 4.35% 13.04% 69.57% 70.00% 30.43% T. cannata G osport 1 223 7.17% 1.35% 7.62% 17.00% 3.59% 2 410 5.61% 0.24% 6.83% 27.00% 7.07% 3 223 4.48% 1.35% 5.83% 28.00% 17.49% 4 386 5.96% 0.78% 4.66% 31.00% 21.76% 5 225 6.22% 1.33% 8.89% 35.00% 10.67% 6 227 6.17% 1.76% 7.05% 37.00% 5.73% T. cannata Lisbon 1 353 11.90% 0.57% 0.57% 86.00% 0.00% 2 22 4.55% 0,00% 0.00% 77.00% 0.00% T. fischeri Moodys (Tcheva Ck.) 1 1 0.00% 0.00% 0.00% 100.00% 0.00% 2 - - - - - - 3 - - - - - - 4 - - - - ■ - 5 4 0.00% 0.00% 25.00% 100.00% 25.00% 6 - - - - - - 7 - - - - - - 8 - - - - - - T able 14: W ithin-species predation and taphonom ic characteristics. M ean values and sam ple sizes for all studied taxa. 92 Taxon Formation (Outcrop) Sam ple u # of Specim ens Mean % Drill Mean % Inetf. M ean % Peel M ean % Bkn Mean % Epis 9 - - - - - - T. ghigna Gosport 1 11 9.09% 0.00% 18.18% 36.00% 0.00% 2 9 0.00% 0.00% 33.33% 0.00% 33.33% 3 8 25.00% 0.00% 25.00% 25.00% 75.00% 4 11 18.18% 0.00% 9.09% 18.00% 36.36% 5 5 0.00% 20.00% 20.00% 60.00% 20.00% 6 1 0.00% 0.00% 0.00% 0.00% 100.00% T. houstonia Lisbon 1 - - - - - - 2 - - - - - ■ T. tisbonensls Lisbon 1 - - ■ - - - 2 - - - - - ■ T. mississippiensis Byram 1 219 2.74% 0.00% 0.00% 82.00% 0,00% 2 181 13.26% 1.10% 1.10% 87.00% 0.55% 3 113 6.19% 0.00% 0.00% 89.00% 3.54% 4 116 1.72% 0.00% 0.00% 90.00% 0.00% 5 102 4.90% 0.98% 0.98% 76.00% 0.00% 6 162 3.09% 0.00% 0.00% 78.00% 0.00% 7 112 7.14% 1.79% 1.79% 06.00% 0.00% 8 155 4.52% 0.00% 0.00% 92.00% 0.00% 9 151 8.61% 0.00% 0.00% 84.00% 0.00% 10 217 3.23% 0.00% 0.00% 81.00% 0.46% 11 187 2.14% 0.53% 0.53% 86.00% 0.00% 12 93 7.53% 0.00% 0.00% 82.00% 0.00% T. nasuta Stone City 1 22 13.64% 0.00% 0.00% 100.00% 18.18% 2 32 0.00% 0.00% 0.00% 75.00% 0.00% 3 166 11.29% 1.00% 1.08% 95.00% 0.00% 4 23 4.35% 0.00% 0.00% 87.00% 0.00% 5 21 4.76% 0.00% 0.00% 90.00% 0.00% T. obruta Gosport 1 17 11.76% 0.00% 29.41% 6.00% 0.00% 2 6 16.67% 0.00% 0.00% 17.00% 25.00% 3 4 0.00% 0.00% 25.00% 0.00% 5.38% 4 8 12.50% 0.00% 25.00% 12.00% 13.04% 5 2 0.00% 0.00% 50.00% 0.00% 9.52% 6 • ■ - - • - T. perdita Moodys (Chick R.) 1 102 2.94% 0.98% 13.73% 79.00% 12.75% 2 488 1.84% 0.00% 5.12% 92.00% 15.16% 3 570 1.58% 0.18% 7.37% 80.00% 16.67% 4 181 4.97% 0.00% 28.18% 83.00% 51.38% 5 140 5.00% 2.14% 25.71% 79.00% 30.00% T. perdita Moodys (LeFleurs) 1 168 10.71% 2.98% 5.95% 65.00% 0.60% 2 113 9.73% 0.88% 15.04% 58.00% 1.77% 3 40 12.50% 0.00% 17.50% 57.00% 2.50% T. perdita Moodys (Tcheva Ck.) 1 335 12.24% 1.49% 4.18% 75.00% 2.69% 2 36 2.78% 0.00% 19.44% 81.00% 5.56% 3 318 5.03% 0.94% 8.18% 61.00% 6.60% 4 201 4.98% 2.99% 5.97% 66.00% 7.96% 5 201 5.47% 1.00% 6.97% 64.00% 12.44% 6 28 7.14% 3.57% 10.71% 86.00% 7.14% 7 171 5.26% 1.75% 18.13% 75.00% 14.62% 8 87 6.90% 3.45% 13.79% 60.00% 14.94% 9 99 5.05% 1.01% 27.27% 75.00% 33.33% Table 14: (continued) 93 Moodys Branch Formation Seventeen two-liter sam ples of the Moodys Branch Formation were collected from three different outcrops, including Tcheva Creek, LeFleur's Bluff (n=3), and the Chickasawhay River (n=5) in Mississippi {Figs. 11-13). Taxa at these outcrops include T. aiveata, T. fischeri, and T. perdita. (Fig. 17d,f,k). The nine sam ples collected from Tcheva Creek contain three different species of turritelline gastropods, including T. aiveata, T. fischeri, and T. perdita {Figs. 17d,f,k). Average drilling intensity estim ates range from 0% to 20% for T. aiveata (n=9), are 0% for T. fischeri (n=2), and range from 3% to 12% for T. perdita (n=9; Table 14). M easured sam ple sizes range from 30 to 341 shells per two-liter sam ple (n=1567). Significant variability in drilling intensity is not observed within these sam ples. Average drilling inefficiency estim ates range from 0% to 13% for T. aiveata (n=9), are 0% for T. fischeri (n=2), and range from 0% to 4% for T. perdita (n=9). M easured sam ple sizes range from 30 to 341 shells per two-liter sam ple (n=1567). Significant variability in drilling inefficiency is observed in 1 of the 8 sam ples (p<0.05). Average peeling intensity estim ates range from 0% to 70% for T. aiveata (n=9), from 0% to 25% for T. fischeri (n=2), and from 4% to 27% for T. perdita (n=9). M easured sam ple sizes range from 30 to 341 shells per two-liter sample (n=1567). Significant variability in peeling intensity is observed in 6 of 9 sam ples (p<0.05). Of these, highly significant variability is observed in two sam ples (p<0.01) and very highly significant variability is observed in two sam ples (p<0.001). The three two-liter sam ples collected from LeFleur's Bluff have two species of turritelline gastropods, including T. aiveata and T. perdita (Fig. 17d,k). Average drilling intensity estim ates are 0% for T. aiveata (n=3) and 94 range from 10% to 13% for T. perdita (n=3; Table 14). M easured sam ple sizes range from 41 to 170 shells per two-liter sam ple (n=326). Significant variability in drilling intensity is not observed in th e se sam ples. A verage drilling inefficiency estim ates are 0% for T, aiveata (n=3) and range from 0% to 3% for T. perdita (n=3). M easured sam ple sizes range from 41 to 170 shells per two- liter sam ple (n=326). Significant variability in drilling inefficiency is not observed in th e s e sam ples. A verage peeling intensity estim ates range from 0% to 100% for T. aiveata (n=3), and range from 6% to 18% for T. perdita (n=3). M easured sam p les siz es range from 41 to 170 individuals p er two-liter sam ple (n=326). Significant variability in peeling intensity is observed in 2 of th e 3 sam p les (p<0.05). Highly significant variability is observed in one of th e s e two sam p les (p<0.01). T he five two-liter sam p les collected from the C hickasaw hay River have the sa m e two sp ecies, T. aiveata and T. perdita (Fig. 17d,k). A verage drilling intensity estim ates range from 0% to 13% for T. aiveata (n=5) and from 2% to 5% for T. perdita (n=5; Table 14). M easured sam ple siz es range from 118 to 633 shells p er two-liter sam ple (n=1705). Significant differences in av erag e drilling intensity are not observed in th e se sam p les. A verage drilling inefficiency estim ates range from 0% to 6% for T. aiveata (n=5) and from 0% to 2 % for T. perdita (n=5). M easured sam ple siz es range from 118 to 633 shells per two-liter sam p le (n=1705). Significant variability in drilling inefficiency is observed in 1 of the 4 sam p les available for study (p<0.05). A verage peeling intensity estim ates range from 5% to 23% for T. aiveata (n=5) and from 5% to 28% for T. perdita (n=5). M easured sam ple siz es range from 118 to 633 shells 95 per two-liter sam ple (n=39). Significant variability in peeling intensity is not observed in th e se sam ples. Lisbon Formation Two two-liter sam ples of the Lisbon Formation w ere collected from an outcrop along the Tom bigbee River (Fig. 7) and contain two sp ecies of turritelline gastropods, including M. claibornensis and T. carinata (Fig. 17a,e). A verage drilling intensity estim ates range from 5% to 36% for M. claibornensis (n=2) and from 5% to 12% for T. carinata (n=2; Table 14). M easured sam ple siz es range from 24 to 406 shells per two-liter sam ple (n=428). Significant variability in drilling intensity are observed in both sam ples (p<0.05). Very highly significant variability exists in one of the two sam ples (p<0.001). This is the sa m e sam ple which contains the larger num ber of individuals. A verage drilling inefficiency estim ates range from 0% to 19% for M. claibornensis (n=2) and from 0% to 1 % for T. carinata (n=2). M easured sam ple sizes range from 24 to 406 shells per two-liter sam ple (n=432). Very highly significant variability in drilling inefficiency is observed in one of the two sam ples (p<0.001). This is the sa m e sam ple which contains the larger num ber of individuals. A verage peeling intensity estim ates range from 0% to 40% for M. claibornensis (n=2) and from 0% to 6% for T. carinata (n=2). M easured sam ple sizes range from 24 to 406 shells per two-liter sam ple (n=432). Very highly significant variability in peeling intensity is observed in one of the two sam ples (p<0.001). Gosport Sand Six two-liter sam ples of the Gosport Sand w ere collected from a locality at Little Stave Creek (Fig. 9) and have five different species of turritelline gastropods, M. vetusta, T. apita, T. carinata, T. ghigna, and T. obruta (Fig. 96 17b,c,e,g,j). Average drilling intensity estim ates range from 8% to 17% for M. vetusta (n=5), from 0% to 100% for T. apita (n=5), from 4% to 7% for T. carinata (n=5), from 0% to 25% for T. ghigna (n=5), and from 0% to 17% for T. obruta (n=4; Table 14). M easured sam ple sizes range from 320 to 643 shells per two- liter sam ple (n=2667). Significant variability in drilling intensity is observed in two of the six sam ples (p<0.05). One of these sam ples exhibits highly significant variability (p<0.01). Average drilling inefficiency estim ates range from 1% to 9% for M. vetusta (n=6), are 0% for T. apita (n=6), range from 1% to 2% for T. carinata (n=6), range from 0% to 20% for T. ghigna (n=6), and are 0% for T. obruta (n=5). M easured sam ple sizes range from 320 to 643 shells per two-liter sam ple (n=2666). Highly significant variability in drilling inefficiency is observed in 1 of the 6 sam ples {p<0.01). Average peeling intensity estim ates range from 5% to 14% for M. vetusta (n=6), are 0% for T. apita (n=6), range from 5% to 9% for T. carinata (n=6), range from 0% to 33% for T. ghigna (n=6), and range from 0% to 50% for T. obruta (n=5). M easured sam ple sizes range from 320 to 643 shells per two-liter sam ple (n=2666). Significant variability in peeling intensity is observed in 2 of the 6 sam ples (p<0.05). Summary Significant variability betw een constituent taxa is observed in predation param eters at all of the studied outcrops. Significant variability is observed in drilling intensity in 5 out of 30 sam ples, in drilling efficiency in 4 out of 20 sam ples, and in peeling intensity in 12 out of 29 sam ples (Table 12). 97 Mixed Species: Between Sam ples Sam ples were collected at six outcrops of the Gosport (n=1), Lisbon (n=1), Stone City (n=1), and Moodys Branch (n=3). Sam ples from each outcrop w ere com pared to one another to determine variability betw een two-liter sam ples (Fig. 3). Average drilling intensity estim ates range from 5% to 24% in Gosport sam ples (n=6), from 24% to 27% in Lisbon sam ples (n=2), from 11% to 17% in Stone City sam ples (n=5), from 2% to 9% in Moodys Branch sam ples from the Chickasawhay River (n=5), from 5% to 6% in Moodys Branch sam ples from LeFleur's Bluff (n=3), and from 2% to 11% in Moodys Branch sam ples from Tcheva Creek (n=9; Table 15). Significant variability in drilling intensity betw een sam ples is not observed at any of these six outcrops. Average drilling inefficiency estim ates range from 1% to 6% in Gosport sam ples (n=6), from 0% to 10% in Lisbon sam ples (n-2), from 0% to 1% in Stone City Sam ples (n=5), from 0% to 4% in Moodys Branch sam ples from the Chickasawhay River (n=5), from 0% to 1% in Moodys Branch sam ples from LeFleur's Bluff (n=3), and from 0% to 7% in Moodys Branch sam ples from Tcheva Creek (n=9; Table 15). Very highly significant variability in drilling inefficiency is observed in one of these six outcrops (p<0.001). Average peeling intensity estim ates range from 4% to 18% in Gosport sam ples (n=6), from 0% to 23% in Lisbon sam ples (n=2), from 6% to 29% in Stone City sam ples (n=5), from 5% to 25% in Moodys Branch sam ples from the Chickasawhay River (n=5), from 3% to 58% in Moodys Branch sam ples from LeFleur's Bluff (n=3), and from 5% to 48% in Moodys Branch sam ples from 98 Formation (Outcrop) Sam ple # # of Taxa Mean % Drill Mean % Ineff Mean % Peel Mean % Bkn Mean % Epis Gosport 1 5 8.98% 1.35% 13.93% 90.00% 82.51% 2 5 8.98% 0.20% 9.23% 82.00% 88.27% 3 5 8.68% 1.59% 12.09% 60.00% 86.66% 4 5 9.29% 0.75% 9.11% 60.00% 76.66% 5 5 23.82% 6.05% 17.76% 80.00% 78.89% 6 4 4.84% 1.54% 4.23% 71.00% 82.34% Lisbon 1 2 27.27% 0.00% 0.00% 100.00% 61.36% 2 2 23.87% 9.72% 22.64% 91.00% 22.61% M oodys (Chick R.) 1 2 7.72% 3.62% 9.99% 69.00% 10.29% 2 2 2.32% 0.47% 4.90% 84.00% 10.80% 3 2 3.17% 0.09% 10.83% 85.00% 22.08% 4 2 2.49% 0.00% 25.45% 56.00% 17.38% 5 2 8.75% 1.07% 19.11% 66.00% 16.96% Moodys (LeFleurs) 1 2 5.36% 1.49% 2.98% 75.00% 17.26% 2 2 4.87% 0.44% 57.52% 99.00% 46.24% 3 2 6.25% 0.00% 57.52% 99.00% 21.25% Moodys (Tcheva Ck.) 1 3 10.75% 0.50% 14.73% 99.00% 14,93% 2 2 9.72% 0.00% 34.72% 97.00% 18.06% 3 2 2.52% 0.47% 29.09% 97.00% 19.34% 4 2 2.49% 1.49% 2.99% 96.00% 67.16% 5 3 1.82% 0.33% 21.77% 82.00% 11.94% 6 3 1.82% 1.79% 5.36% 82.00% 32.14% 7 2 5.26% 0.88% 38.01% 87.00% 15.20% 8 2 5.83% 4.11% 28.33% 90.00% 27.26% 9 2 4.70% 7.03% 48.42% 68.00% 16.97% Stone City 1 2 16.82% 0.00% 11.82% 91.00% 0.00% 2 2 16.67% 0.00% 6.25% 100.00% 12.50% 3 2 11.20% 1.15% 21.54% 99.00% 10.71% 4 2 14.67% 1.15% 14.67% 100.00% 25.27% 5 2 16.67% 1.15% 28.57% 100.00% 19.05% Table 15: M ixed-species predation and taphonom ic characteristics. Mean values and sam ple sizes used to analyze betw een-sam ple variability. 99 Tcheva Creek (n=9; Table 15). Significant variability in peeling intensity is not observed in any of th ese six outcrops. Summary W hen utilizing m ixed-species sam ple m eans to analyze differences betw een sam ples, significant variability is observed in one of the six studied outcrops (Table 4). Significant variability is noted in drilling efficiency estim ates, but is not noted in estim ates of drilling or peeling intensity. Mixed Species: Between Outcrops Two-liter sam ples were collected at three outcrops of the Moodys Branch Formation in order to a s s e s s variability betw een different outcrops of the sam e formation. T hese included outcrops at the Chickasawhay River, Tcheva Creek, and at LeFleur's Bluff (Figs. 11-13). Average drilling intensity estim ates are all close to 5% at each outcrop (Table 5). Mean drilling intensity estim ates for each outcrop are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean drilling intensity estim ates is not observed betw een these three outcrops. Average drilling inefficiency estim ates range from 2% to 5% (Table 5). Mean drilling inefficiency estim ates for each outcrop are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur’s Bluff. Significant variability in m ean drilling inefficiency estim ates is not observed betw een these three outcrops. Average peeling intensity estim ates range from 14% to 39% (Table 5). Mean peeling intensity estim ates for each outcrop are based on 9 sam ples at 100 Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean peeling intensity estim ates is not observed betw een th ese three outcrops. Summary W hen utilizing m ixed-species sam ple m eans to analyze differences betw een outcrops, significant variability is not observed in any of the studied param eters. Results are sum m arized in Table 6. Mixed Species: Between Formations Four formations from the sam e epoch were com pared to one another in order to a s s e s s variability betw een them . T hese included the Gosport, Lisbon, Moodys Branch, and Stone City Formations (Fig. 3). Average drilling intensity estim ates for each formation range from 5% to 26% (Table7). Mean drilling intensity estim ates are based on 6 sam ples in the Gosport Sand, 2 sam ples in the Lisbon Formation, 17 sam ples in the Moodys Branch Formation, and 5 sam ples in the Stone City Beds. Very highly significant variability in m ean drilling intensity is observed betw een th ese 4 form ations (p<0.001). Average drilling inefficiency estim ates for each formation range from 1 % to 5% (Table 7). Mean drilling inefficiency estim ates are b ased on 6 sam ples in the Gosport Sand, 2 sam ples in the Lisbon Formation, 17 sam ples in the Moodys Branch Formation, and 5 sam ples in the Stone City Beds. Significant variability in drilling inefficiency is not observed betw een th ese 4 formations. 101 Average peeling intensity estim ates for each formation range from 11% to 24% (Table 7). Mean peeling intensity estim ates are based on 6 sam ples from the Gosport Sand, 2 sam ples from the Lisbon Formation, 17 sam ples from the Moodys Branch Formation, and 5 sam ples from the Stone City Beds. Significant variability in m ean peeling intensity is not observed between these 4 formations. Summary When utilizing mixed-species sample m eans to analyze differences between formations, significant variability is observed in one of the three studied param eters, drilling intensity. Results are summarized in Table 8. Within Species: Between Sam ples Eleven species of turritelline gastropods were examined from 7 outcrops of 5 different formations in order to a sse ss within-species patterns of variability in predation characteristics. Studied taxa include Mesaiia claibornensis, M. vetusta, Turritelia apita, T. aiveata, T. carinata, T. fischeri, T. ghigna, T. mississippiensis, T. nasuta, T. obruta, and T. perdita (Fig. 17). Mesaiia Claibornensis Seven sam ples of M. claibornensis (Fig. 17a) were collected from outcrops of the Stone City Beds along the Brazos River and from the Lisbon Formation along the Tombigbee River (Figs. 5,7). Average drilling intensity estim ates for each sam ple from the Lisbon Formation range from 36% to 50% (n=2; Table 14). M easured shell abundances range from 2 to 53 specim ens per two-liter sam ple (n=55). 102 Significant variability in m ean drilling intensity is not observed betw een th e se sam p les. A verage drilling inefficiency estim ates for each sam ple range from 0% to 19% (n=2). M easured shell ab u n d an ces range from 2 to 53 specim ens per two-liter sam ple (n=55). Significant variability in m ean drilling inefficiency is not observed betw een th e se sam ples. A verage peeling intensity estim ates for e ac h sam ple range from 0% to 40% (n=2). M easured shell a b u n d an c es range from 2 to 53 sp ecim en s per two-liter sam ple (n=55). Significant variability in peeling intensity is not observed betw een th e se sam ples. A verage drilling intensity estim ates for each sam ple from the S tone City B eds range from 11% to 33% (n=5; T able 14). M easured shell ab u n d an ces range from 3 to 81 specim ens p er two-liter sam ple (n=109). Significant variability in drilling intensity is not observed betw een th e s e sam ples. A verage drilling inefficiency estim ates for each sam ple range from 0% to 1% (n=5). M easured shell ab u n d an ces range from 3 to 81 sp ecim en s per two-liter sam ple (n=109). Significant variability in drilling inefficiency is not o bserved betw een th e s e sam ples. A verage peeling intensity estim ates for each sam ple range from 0% to 43% (n=5). M easured shell ab u n d an ces range from 3 to 81 sp ecim en s per two-liter sam ple (n=109). Significant variability in peeling intensity is not observed betw een th ese sam ples. Mesaiia vetusta Six sam p les of M. vetusta (Fig. 17b) w ere collected from an outcrop of the G osport S and at Little S tave C reek (Fig. 9). A verage drilling intensity estim ates for e ac h sam ple range from 10% to 17% (n=6; Table 14). M easured shell a b u n d an c es range from 91 to 235 specim ens per two-liter sam ple (n=878). Significant variability in drilling intensity is not observed betw een th e se 103 sam p les. A verage drilling inefficiency estim ates for each sam ple range from 1 % to 9% (n=6). M easured shell ab u n d an ces range from 91 to 235 specim ens p er two-liter sam ple (n=878). Significant variability in drilling inefficiency is o bserved betw een th e se sam p les (p<0.05). A verage peeling intensity estim ates for each sam ple range from 5% to 14% (n=6). M easured shell a b u n d an c es range from 91 to 235 specim ens per two-liter sam ple (n=878). Significant variability in peeling intensity is observed betw een th e se sam p les {p<0.05). Turritella apita Six sam p les of T. apita (Fig. 17c) w ere collected from an outcrop of th e G osport S and a t Little S tave C reek (Fig. 9). A verage drilling intensity estim ates for each sam ple range from 0% to 100% (n=6; T able 14). M easured shell a b u n d an c es range from 1 to 3 specim ens p er sam ple (n=12). Lack of multiple shells in several sam p les a s well a s lack of inefficient and peeled shells m akes analysis of variance u n n ecessary (b ecau se th ere is no variance in each sam ple). Turritella aiveata S ev en teen sam p les of T. aiveata (Fig. 17d) w ere collected from 3 outcrops of the Moodys Branch Formation at outcrops at th e C hickasaw hay River, LeFleur's Bluff, and T cheva C reek in M ississippi (Figs. 11-13). A verage drilling intensity estim ates for each sam ple from the C hickasaw hay River outcrop range from 0% to 13% (n=5; T able 14). M easured shell a b u n d an c es range from 16 to 107 specim ens per two-liter sam ple (n=224). Significant variability in drilling intensity estim ates is not observed betw een th e se sam ples. A verage drilling inefficiency estim ates for each 104 sam ple range from 0% to 6% (n=5). M easured shell abundances range from 16 to 107 specim ens per two-liter sam ple (n=224). Significant variability in drilling inefficiency estim ates is not observed betw een th ese sam ples. A verage peeling intensity estim ates for each sam ple range from 5% to 23% (n=5). M easured shell ab u n d an ces range from 16 to 107 specim ens per two-liter sam ple (n=224). Significant variability in peeling intensity is not observed betw een th ese sam ples. Average drilling intensity estim ates for each sam ple from LeFleur's Bluff are all 0% (n— 3; Table 14). M easured shell abundances range from 1 to 2 specim ens per two-liter sam ple (n=5). No variability exists betw een th ese sam ple averages. A verage drilling inefficiency estim ates for each sam ple from LeFleur's Bluff are all 0% (n=3). M easured shell abundances range from 1 to 2 specim en s per two-liter sam ple (n=5). No variability exists betw een th ese sam ple averages. A verage peeling intensity estim ates for each sam ple from LeFleur's Bluff range from 0% to 100% (n=3). M easured shell abundances range from 1 to 2 specim ens per two-liter sam ple (n=5). Lack of multiple specim ens in one of th ese sam ples m akes analysis of variability unnecessary. A verage drilling intensity estim ates for each sam ple from T cheva C reek range from 0% to 17% (n=9; Table 14). M easured shell ab u n d an ces range from 2 to 23 specim ens per two-liter sam ple (n=86). Significant variability in drilling intensity is not observed betw een th ese sam ples. A verage drilling inefficiency estim ates for each sam ple range from 0% to 13% (n=9). M easured shell ab u n d an ces range from 2 to 23 specim ens per two-liter sam ple (n=86). Significant variability in drilling inefficiency is not observed betw een th e se sam ples. A verage peeling intensity estim ates for each sam ple range from 0% 105 to 69% (n=9). M easured shell abundances range from 2 to 23 specim ens per two-liter sam ple (n=86). Significant variability in peeling intensity is not observed betw een th ese sam ples. Turritella carinata Eight sam ples of T. carinata (Fig. 17e) were collected from the Gosport and Lisbon Formations at Little Stave Creek and the Tombigbee River, respectively (Figs.7,9). Average drilling intensity estim ates for each sam ple from the Gosport range from 4% to 7% (n=6; Table 14). M easured shell abundances range from 223 to 410 specim ens per two-liter sam ple (n=1694). Significant variability in drilling intensity is not observed betw een these sam ples. Average drilling inefficiency estim ates for each sam ple range from 0% to 2% (n=6). M easured shell abundances range from 223 to 410 specim ens per two-liter sam ple (n=1694). Significant variability in drilling inefficiency is not observed betw een th ese sam ples. Average peeling intensity estim ates for each sam ple range from 5% to 9% (n=6). M easured shell abundances range from 223 to 410 specim ens per two-liter sam ple (n=1694). Significant variability in peeling intensity is not observed betw een these sam ples. Average drilling intensity estim ates for each sam ple from the Lisbon range from 55 to 12% (n=2; Table 14). M easured shell abundances range from 22 to 353 specim ens per two-liter sam ple. Significant variability in drilling intensity is not observed betw een these sam ples. Average drilling inefficiency estim ates for each sam ple range from 0% to 1% (n=2). M easured shell abundances range from 22 to 353 specim ens per two-liter sam ple (n=375). Significant variability in drilling inefficiency is not observed betw een these 106 sam ples. A verage peeling intensity estim ates for each sam ple range from 0% to 6% (n=2). M easured shell abundances range from 22 to 353 specim ens per two-liter sam ple (n=375). Significant variability in peeling intensity is not observed betw een th e se sam ples. Turritella fischeri Two sam ples of T. fischeri (Fig. 17f) w ere collected from the Moodys Branch Formation at T cheva C reek (Fig. 12). Analysis of variance in drilling intensity and drilling inefficiency estim ates is not calculated b ecau se none of the sam p les contained drilled shells (thus, no variance). A verage peeling intensity estim ates for each sam ple range from 0% to 25 % (n=2; Table 14). M easured shell a b u n d an ces range from 1 to 4 specim ens per two-liter sam ple (n=5). Significant variability in peeling intensity is not observed betw een th ese sam ples. Turritella ghiana Six sam ples of T. ghigna (Fig. 17g) w ere collected from the G osport Sand at Little Stave C reek (Fig. 9). A verage drilling intensity estim ates for each sam ple range from 0% to 25% (n=6). M easured shell ab u n d an ces range from 1 to 11 specim ens per two-liter sam ple (n=45). Significant variability in drilling intensity is not observed betw een th ese sam ples. A verage drilling inefficiency estim ates for each sam ple range from 0% to 20% (n=6). M easured shell ab u n d an ces range from 1 to 11 specim ens per two-liter sam ple (n=45). Significant variability in drilling inefficiency is not observed betw een th e se sam ples. A verage peeling intensity estim ates for each sam ple range from 0% to 33% (n=6). M easured shell abundances range from 1 to 11 specim ens per 107 two-liter sam p le (n=6). Significant variability in peeling intensity is not observed betw een th e s e sam ples. Turritella mississippiensis Twelve sam p les of T. mississippiensis (Fig. 17h) w ere collected from the Byram Form ation at Tallahalla C reek in M ississippi (Fig. 15). A verage drilling intensity estim ates for each sam ple range from 2% to 13% (n=12; T able 14). M easured shell a b u n d an c es range from 93 to 219 sp ecim en s p e r two-liter sam ple (n=1808). Very highly significant variability in drilling intensity is o bserved betw een th e se sam p les (p<0.001). A verage drilling inefficiency estim ates for each sam ple range from 0% to 2% (n=12). M easured shell a b u n d an c es range from 93 to 219 sp ecim en s per two-liter sam ple (n=1808). Significant variability in drilling inefficiency is not observed betw een th e se sam ples. A verage peeling intensity estim ates for each sam ple range from 0% to 5% (n=12). M easured shell a b u n d an c es range from 93 to 219 specim ens per two-liter sam ple (n=1808). Significant variability in peeling intensity is not observed betw een th e se sam ples. Turritella nasuta Five sam ples of T. nasuta (Fig. 17i) w ere collected from th e S tone City B eds along the B razos River (Fig. 5). A verage drilling intensity estim ates for e ach sam p le range from 0% to 14% (n=5; Table 14). M easured shell a b u n d a n c e s range from 21 to 186 specim en s per two-liter sam ple (n=284). Significant variability in drilling intensity is not observed betw een th e se sam ples. A verage drilling inefficiency estim ates for e ac h sam ple range from 0% to 1% (n=5). M easured shell ab u n d an ces range from 21 to 186 specim en s per two-liter sam ple (n=284). Significant variability in drilling inefficiency is not 108 observed betw een th e se sam ples. Average peeling intensity estim ates for each sam ple range from 4% to 14% (n=5). M easured shell abundances range from 21 to 186 specim ens per two-liter sam ple (n=284). Significant variability in peeling intensity is not observed betw een th ese sam ples. Turritella obruta Five sam ples of T. obruta (Fig. 17j) w ere collected from the G osport Sand at Little Stave C reek (Fig. 9). Average drilling intensity estim ates for each sam ple range from 0% to 17% (n=5). M easured shell abundances range from 2 to 17 specim ens per two-liter sam ple (n=37). Significant variability in drilling intensity is not observed betw een th ese sam ples. A verage drilling inefficiency estim ates for each sam ple are all 0% and hence do not exhibit any variability (n=5). M easured shell abundances range from 2 to 17 specim ens per two-liter sam ple (n=37). A verage peeling intensity estim ates for each sam ple range from 0% to 50% (n=5). M easured shell ab u n d an ces range from 2 to 17 specim ens per two-liter sam ple (n=37). Significant variability in peeling intensity is not observed betw een th ese sam ples. Turritella perdita S eventeen sam ples of T. perdita (Fig. 17k) w ere collected from 3 outcrops of the Moodys Branch Formation at outcrops at the Chickasaw hay River, LeFleur's Bluff, and Tcheva Creek in Mississippi (Figs. 11-13). A verage drilling intensity estim ates for each sam ple from the Chickasaw hay River range from 2% to 5% (n=5; Table 14). M easured shell ab u n d an ces range from 102 to 570 specim ens per two-liter sam ple (n=1481). Significant variability in drilling intensity is observed betw een th e se sam ples (p<0.05). A verage drilling inefficiency estim ates for each sam ple range from 109 0% to 2% (n=5). M easured shell abundances range from 102 to 570 specim ens per two-liter sam ple (n=1481). Highly significant variability in drilling inefficiency is observed between these sam ples (p<0.01). Average peeling intensity estim ates for each sam ple range from 5% to 28% (n=5). M easured shell abundances range from 102 to 570 specim ens per two-liter sam ple (n=1481). Very highly significant variability in peeling intensity is observed betw een th ese sam ples (p<0.001). Average drilling intensity estim ates for each sam ple from LeFleur's Bluff range from 10% to 13% (n=3; Table 14). M easured shell abundances range from 40 to 168 specim ens per two-liter sam ple (n=321). Significant variability in drilling intensity is not observed betw een th ese sam ples. Average drilling inefficiency estim ates for each sam ple range from 0% to 3% (n=3). M easured shell abundances range from 40 to 168 specim ens per two-liter sam ple (n=321). Significant variability in drilling inefficiency is not observed betw een th ese sam ples. Average peeling inefficiency estim ates for each sam ple range from 6% to 18% (n=3). M easured shell abundances range from 40 to 168 specim ens per two-liter sam ple (n=342). Significant variability in peeling intensity is observed between th ese sam ples (p<0.05). Average drilling intensity estim ates for each sam ple from Tcheva Creek range from 3% to 12% {n=9; Table 14). M easured shell abundances range from 28 to 335 per two-liter sam ple (n=1478). Highly significant variability in drilling intensity is observed between these sam ples (p<0.01). Average drilling inefficiency estim ates for each sam ple range from 0% to 4% (n=9). M easured shell abundances range from 28 to 335 specim ens per two-liter sam ple (n=1478). Significant variability in drilling inefficiency is not observed betw een 110 th ese sam ples. Average peeling intensity estim ates for each sam ple range from 4% to 27% (n=9). M easured shell abundances range from 28 to 335 specim ens per two-liter sam ple (n=1478). Very highly significant variability in peeling intensity is observed between th ese sam ples (p<0.001). Summary Utilizing individual taxa, significant differences w ere noted betw een sam ples in all predation param eters {Table 9). Analysis of drilling intensity reveals significant variability betw een sam ples in 3 out of 14 taxa. Similarly, significant variability in drilling efficiency and peeling intensity is observed in 2 out of 13 taxa and 4 out of 15 taxa, respectively. Within Species: Between Outcrops Seventeen two-liter sam ples were collected at three outcrops of the Moodys Branch Formation at the Chickasawhay River, Tcheva Creek, and at LeFleur's Bluff in order to a sse ss variability betw een different outcrops of the sam e formation (Figs. 11-13). T hese outcrops have two species of turritelline gastropods which are common to both--7 " . aiveata and T. perdita (Fig. 17d,k). Average drilling intensity estim ates for T. aiveata range from 0% to 7% (n=3; Table 10). Mean drilling intensity estim ates for each outcrop are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean drilling intensity is not observed betw een th ese three outcrops. Average drilling inefficiency estim ates range from 0% to 6% (n=3; Table 10). Mean drilling inefficiency estim ates for each outcrop are based on 9 111 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean drilling inefficiency is not observed betw een these three outcrops. A verage peeling intensity estim ates range from 12% to 67% (Table 10). Mean peeling intensity estim ates are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur’ s Bluff. Significant variability in m ean peeling intensity is not observed between these three outcrops. A verage drilling intensity estim ates for T. perdita range from 3% to 11% (n— 3: Table 10). Mean drilling intensity estim ates for each outcrop are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Highly significant variability in m ean drilling intensity is observed betw een these three outcrops (p<0.01). Average drilling inefficiency estim ates range from 1% to 2% (n=3; Table 10). Mean drilling inefficiency estim ates for each outcrop are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in m ean drilling inefficiency is not observed betw een th ese three outcrops. Average peeling intensity estim ates range from 13% to 16% (n=3; Table 10). Mean peeling intensity estim ates for each outcrop are b ased on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in peeling intensity is not observed betw een th ese three outcrops. 112 Summary Using individual taxa to a sse ss variability, significant variability betw een outcrops of the sam e formation is observed in one out of two taxa (Table 11). Significant variability betw een outcrops is observed in both epibiont presence and shell breakage param eters. Within Species: Betw een Formations Four formations from the sam e epoch were com pared to one another in order to a s s e s s variability betw een them. T hese included the Gosport, Lisbon, Moodys Branch, and Stone City Formations (Fig. 3). Turritelline gastropod species common to the Stone City and Lisbon Formations include M. claibornensis (Fig. 17a). Turritelline gastropod species common to the Gosport and Lisbon Formations include T. carinata (Fig. 17e). Average drilling intensity estim ates for M. claibornensis range from 24% to 43% (n=2; Table 12). Mean drilling intensity estim ates for each formation are based on 5 sam ples in the Stone City Beds and 2 sam ples in the Lisbon Formation. Significant variability in m ean drilling intensity is observed betw een these 2 formations (p<0.05). Average drilling inefficiency estim ates range from 1% to 10% (n=2; Table 12). M ean drilling inefficiency estim ates for each formation are b ased on 5 sam ples in the Stone City Beds and 2 sam ples in the Lisbon Formation. Significant variability in m ean drilling inefficiency is not observed betw een these 2 formations. Average peeling intensity estim ates range from 20% to 21% (n=2; Table 12). M ean peeling intensity estim ates for each formation are based on 5 113 sam ples in the S tone City B eds and 2 sam ples in the Lisbon Formation. Significant variability in m ean peeling intensity is not observed betw een th ese 2 form ations. A verage drilling intensity estim ates for T. carinata range from 6% to 8% (n=2; Table 12). Mean drilling intensity estim ates for each formation are b ased on 6 sam p les in the Gosport Sand and 2 sam ples in the Lisbon Formation. Significant variability in m ean drilling intensity is not observed betw een th ese 2 form ations. Average drilling inefficiency estim ates range from 0% to 1% (n=2; Table 12). M ean drilling inefficiency estim ates for each formation are b ased on 6 sam ples in the G osport Sand and 2 sam ples in the Lisbon Formation. Significant variability in m ean drilling inefficiency is not observed betw een th ese 2 formations. A verage peeling intensity estim ates range from 3% to 6% (n=2; Table 12). M ean peeling intensity estim ates for each formation are based on 6 sam ples in the G osport Sand and 2 sam ples in the Lisbon Formation. Significant variability in m ean peeling intensity is not observed betw een th ese 2 form ations. Summary Using individual taxa to a s s e s s variability betw een form ations of similar age, significant variability is observed in one of two taxa (Table 13). However, significant variability is only observed in drilling intensity param eters. 114 Taphonomic Characteristics Betw een Species: Within Sam ples Stone City Beds Five two-liter sam ples of the Stone City Beds w ere collected from an outcrop along the Brazos River in T exas (Fig. 5) and contain two sp ecies of turritelline gastropods, M. claibornensis and T. nasuta (Fig. 17a,i). A verage shell breakage estim ates range from 62% to 100% for M. claibornensis (n=5) and from 75% to 100% for T. nasuta (n=5; Table 14). M easured sam ple sizes range from 28 to 267 shells per two-liter sam ple (n=393). Highly significant variability in m ean shell breakage is observed in one of the 5 sam ples (p<0.001). A verage epibiont presence estim ates range from 0% to 2% for M. claibornensis (n=5) and from 0% to 18% for T. nasuta (n=5). M easured sam ple sizes range from 28 to 267 shells per two-liter sam ple (n=393). Significant variability in epibiont presen ce is observed in one of the five sam ples (p<0.05). Moodvs Branch Formation S eventeen two-liter sam ples of th e Moodys Branch Formation w ere collected from three different outcrops, including T cheva Creek, LeFleur's Bluff (n=3), and the Chickasaw hay River (n=5) in Mississippi (Figs. 11-13). The nine sam ples collected from Tcheva C reek have three different sp ecies of turritelline gastropods, including T. alveata, T. fischeri, and T. perdita (Fig. 17d,f,k). A verage shell breakage estim ates range from 0% to 100% for T. alveata (n=9), are 100% for T. fischeri (n=2), and range from 60% to 86% for 7 * . perdita (n=9; Table 14). M easured sam ple sizes range from 30 to 341 shells per two-liter sam ple (n=1569). Significant variability in shell breakage is 115 observed in 1 of th e se 9 sam ples (p<0.05). A verage epibiont p resen c e estim ates range from 0% to 30% for 7. alveata (n=9), from 0% to 25% for 7. fischeri (n=2), and 3% to 33% for 7. perdita (n=9). M easured sam ple sizes range from 30 to 341 shells per two-liter sam ple (n=1569). Significant variability in epibiont p resen ce is not observed in th e se sam ples. The th ree two-liter sam p les collected from LeFleur's Bluff (Fig. 11) have two sp e c ie s of turritelline gastropods, including 7. alveata and 7. perdita (Fig. 17d,k). A verage shell breakage estim ates range from 50% to 100% for 7. alveata (n=3) and from 5.02 mm to 13.04 mm for 7. perdita (Table 14). M easured sam ple siz es range from 41 to 189 shells per two-liter sam ple (n=401). Significant variability in shell b reakage is not observed in th e se sam ples. A verage epibiont p resen ce estim ates range from 0% to 50% for 7. alveata (n=3) and 1% to 3% for 7. perdita (n=3). M easured sam ple sizes range from 41 to 189 shells per two-liter sam ple (n=401). Very highly significant variability in epibiont p resen ce is observed in one of th e th ree sam p les (p<0.001). The five two-liter sam ples collected from the C hickasaw hay River (Fig. 13) have th e sa m e two species, 7. alveata and 7. perdita (Fig. 17d,k). A verage shell b reak ag e estim ates range from 76% to 100% for 7. alveata (n=5) and from 79% to 92% for 7. perdita (n=5; Table 14). M easured sam ple siz es range from 118 to 633 shells per two-liter sam ple (n=1705). Significant differences in shell breakage is observed in 2 of the 5 sam ples (p<0.05). A verage epibiont p resen ce estim ates range from 13% to 50% for 7. alveata (n=5) and from 13% to 51% for 7. perdita (n=5). M easured sam ple siz es range 116 from 118 to 633 shells per two-liter sam ple (n=1705). Very highly significant variability in epibiont presence is observed in one of the five sam ples (p<0.001). Lisbon Formation Two two-liter sam ples of the Lisbon Formation w ere collected from an outcrop along the Tom bigbee River {Fgi. 7) and contain two species of turritelline gastropods, including M. ciaibornensis, and T. carinata (Fig. 17a,e). A verage shell breakage estim ates range from 69% to 100% for M. ciaibornensis (n=2) and from 78% to 86% for T. carinata (n=2; Table 14). M easured sam ple sizes range from 24 to 405 shells per two-liter sam ple (n=429). Significant variability in shell breakage is observed in both sam ples (p<0.05). Highly significant variability is observed in one of th ese (p<0.01). A verage epibiont presen ce range from 0% to 19% for M. claibornensis (n=2) and are 0% for T. carinata (n=2). M easured sam ple sizes range from 24 to 457 shells per two-liter sam ple (n=481). Very highly significant variability in epibiont coverage is observed in one of the two sam ples (p<0.001). Gosport Sand Six two-liter sam ples of the Gosport Sand w ere collected from a locality at Little Stave Creek, Alabam a (Fig. 9), and have five different sp ecies of turritelline gastropods, M. vetusta, T. apita, T. carinata, T. ghigna, and T. obruta (Fig. 17b,c,e,g,j). A verage shell breakage estim ates range from 11% to 34% for M. vetusta (n=6), from 0% to 33% for T. apita (n=6), from 17% to 37% for T. carinata (n=6), from 0% to 60% for T. ghigna (n=6), and from 0% to 17% for T. obruta (n=5; Table 14). M easured sam ple sizes range from 320 to 643 shells per two-liter sam ple (n=2666). Significant variability in shell breakage is observed in 4 of the 6 sam ples (p<0.05). Very highly significant variability is 117 observed in one of th ese sam ples (p<0.001). Average epibiont presence estim ates range from 11 % to 30% for M. vetusta (n=6), from 0% to 50% for T. apita (n=6), from 4% to 22% for T. carinata (n=6), from 0% to 100% for T. ghigna (n=6), and from 25% to 50% for T. obruta (n=5). M easured sam ple sizes range from 320 to 643 shells per two-liter sam ple (n=2666). Highly significant variability in epibiont presence is observed in four of the six sam ples (p<0.01). Two of these sam ples exhibit very highly significant variability (p<0.001). Summary Significant variability betw een constituent taxa is observed in taphonom ic characteristics at all of the outcrops for which data w as available. Significant variability is observed in epibiont presence in 8 out of 26 sam ples w hereas variability is observed in shell breakage in 10 out of 29 sam ples (Table 2). Mixed Species: Between Sam ples Sam ples at six outcrops of the Gosport (n=1), Lisbon (n=1), Stone City (n=1), and Moodys Branch (n-3) Formations were com pared to one another to determ ine variability betw een two-liter sam ples (Fig. 3). Average shell breakage estim ates range from 12% to 23% in Gosport sam ples (n=6), from 39% to 78% in Lisbon sam ples (n=2), from 75% to 100% in Stone City sam ples (n=5), from 78% to 90% in Moodys Branch sam ples from the Chickasawhay River (n=5), from 54% to 79% in Moodys Branch sam ples from LeFleur's Bluff (n=3), and from 33% to 88% in Moodys Branch sam ples from Tcheva C reek 118 (n=9; Table 15). Significant variability in shell breakage is not observed between sam ples at these outcrops. Average epibiont presence estim ates range from 10% to 40% in Gosport sam ples (n=6), from 0% to 9% in Lisbon sam ples (n=2), from 0% to 9% in Stone City Sam ples (n=5), from 29% to 88% in Moodys Branch sam ples from the Chickasawhay River (n=5), from 1% to 25% in Moodys Branch sam ples from LeFleur's Bluff (n=3), and from 1% to 32% in Moodys Branch sam ples from Tcheva Creek (n=9; Table 15). Very highly significant variability in epibiont presence is observed in one of these six outcrops (p<0.001). Summary When utilizing mixed-species sam ple m eans to analyze differences betw een sam ples, significant variability is observed in one of the six studied outcrops (Table 4). Significant variability is noted in epibiont presence, but is not noted in estim ates of shell breakage. Mixed Species: Between Outcrops Two-liter sam ples were collected at three outcrops of the Moodys Branch Formation at the Chickasawhay River, Tcheva Creek, and at LeFleur's Bluff in order to a s se ss variability between different outcrops of the sam e formation (Fig. 3). Average shell breakage estim ates range from 72% to 85% (n=3; Table 7). Mean shell breakage estim ates for each outcrop are based on 9 sam ples at Tcheva Creek, 5 at the Chickasawhay River, and 3 at LeFleur's Bluff. Significant variability in shell breakage estim ates is not observed between these three outcrops. 119 A verage epibiont p resen ce estim ates range from 9% to 28% (n=3; Table 7). M ean epibiont p resen ce estim ates for each outcrop are b a sed on 9 sam ples at T cheva Creek, 5 at the C hickasaw hay River, and 3 at LeFleur's Bluff. Significant variability in epibiont p resen ce estim ates is observed betw een th e se th ree outcrops (p<0.05). Summary W hen utilizing m ixed-species sam ple m ean s to analyze differences betw een outcrops, significant variability is observed in one of the two studied p aram eters, epibiont p resence. R esults a re sum m arized in Table 6. Mixed S pecies: B etw een Form ations Four form ations from the sam e epoch w ere com pared to one an o th er in order to a s s e s s variability betw een them . T h ese included the G osport, Lisbon, M oodys Branch, and S tone City Form ations (Fig. 3). A verage shell breakage estim ates for each formation range from 17% to 8 6 % (n -4 ; Table 7). M ean shell b reakage estim ates are b a se d on 6 sam p les in th e G osport Sand, 2 sam p les in the Lisbon Formation, 5 sam p les in th e Stone City B eds, and 17 sam ples in the M oodys Branch Formation. Very highly significant variability in m ean shell b reakage is observed betw een th e s e 4 form ations. A verage epibiont p resen ce estim ates for each formation range from 2% to 26% (n=4; Table 7). M ean epibiont p resen ce estim ates a re b ased on 6 sam p les in the G osport Sand, 2 sam p les in the Lisbon Form ation, 5 sam p les in th e S tone City Beds, and 17 sam p les in the Moodys Branch Form ation. 120 Significant variability in m ean epibiont presence is observed betw een th ese 4 form ations (p<0.05). Summary W hen utilizing m ixed-species sam ple m eans to analyze differences betw een formations, significant variability is observed in both of th e studied p aram eters, including epibiont p resen ce and shell breakage. R esults are sum m arized in Table 8. Within Species: Betw een Sam ples Eleven sp ecies of turritelline gastropods w ere exam ined from 7 outcrops of 5 different form ations in order to a s s e s s within-species patterns of variability in taphonom ic characteristics. Studied taxa include Mesalia claibornensis, M. vetusta, Turritella apita, T. alveata, T. carinata, T. fischeri, T. ghigna, T. mississippiensis, T. nasuta, T. obruta, and T. perdita (Fig. 17). Mesalia claibornensis S even sam ples of M. claibornensis (Fig. 17a) w ere collected from outcrops of th e Stone City Beds at the Brazos River and from the Lisbon Formation along the Tom bigbee River (Figs. 5,7). A verage shell breakage estim ates for each sam ple from the Lisbon Formation range from 0% to 70% (n=2; Table 14). M easured shell ab u n d an ces range from 2 to 52 specim ens per two-liter sam ple (n=54). Significant variability in m ean shell breakage is observed betw een th e se sam ples (p<0.05). A verage epibiont p resen ce estim ates for each sam ple range from 0% to 19% (n=2). M easured shell ab u n d an ces range from 2 to 53 specim ens per two-liter sam ple (n=55). 121 Significant variability in m ean epibiont presence is not observed betw een these sam ples. Average shell breakage estim ates for each sam ple from the Stone City Beds range from 62% to 100% {n=5; Table 14). M easured shell abundances range from 3 to 81 specim ens per two-liter sam ple (n=109). Significant variability in shell breakage is not observed betw een these sam ples. Average epibiont presence estim ates for each sam ple range from 0% to 2% (n=5). M easured shell abundances range from 3 to 81 specim ens per two-liter sam ple (n=109). Significant variability in epibiont presence is not observed betw een th ese sam ples. Mesalia vetusta Six sam ples of M. vetusta (Fig. 17b) were collected from an outcrop of the Gosport formation at Little Stave Creek (Fig. 9). Average shell breakage estim ates for each sam ple range from 11% to 34% (n=6; Table 14). M easured shell abundances range from 91 to 235 specim ens per two-liter sam ple (n=878). Very highly significant variability in shell breakage is observed betw een th ese sam ples (p<0.001). Average epibiont presence estim ates for each sam ple range from 11% to 20% (n=6). M easured shell abundances range from 91 to 235 specim ens per two-liter sam ple (n=878). Significant variability in epibiont presence is not observed between these sam ples. Turritella apita Six sam ples of T. apita (Fig. 17c) were collected from an outcrop of the Gosport formation at Little Stave Creek (Fig. 9). Average shell breakage estim ates for each sam ple range from 0% to 33% (n=6). M easured shell abundances range from 1 to 3 specim ens per sam ple (n=12). Significant 122 variability in shell breakage is not observed between these sam ples. Average epibiont presence estim ates for each sample range from 0% to 50% (n=6). Measured shell abundances range from 1 to 3 specim ens per sample (n=12). Significant variability in epibiont presence is not observed between these sam ples. Turritella alveata Seventeen sam ples of T. alveata (Fig. 17d) were collected from 3 outcrops of the Moodys Branch Formation at outcrops at the Chickasawhay River, LeFleur's Bluff, and Tcheva Creek in Mississippi (Figs. 11-13). Average shell breakage estim ates for each sample from the Chickasawhay River outcrop range from 76% to 100% (n=5; Table 14). Measured shell abundances range from 16 to 107 specim ens per two-liter sample (n=224). Significant variability in shell breakage estim ates is not observed between these sam ples. Average epibiont presence estim ates for each sample range from 12% to 50% (n=5). Measured shell abundances range from 16 to 107 specim ens per two-liter sample (n=224). Highly significant variability in epibiont presence estim ates is observed between these sam ples (p<0.01). Average shell breakage estim ates for each sample from LeFleur's Bluff range from 50% to 100% (n=3; Table 14). Measured shell abundances range from 1 to 2 specim ens per two-liter sample (n=5). Significant variability in shell breakage is not observed between these samples. Average epibiont presence estim ates for each sample from LeFleur's Bluff range from 0% to 50% (n=3). Measured shell abundances range from 1 to 2 specim ens per two-liter sample (n=5). Significant variability in epibiont presence is not observed between these samples. 123 A verage shell breakage estim ates for each sam ple from T cheva C reek range from 0% to 100% (n=9; Table 14). M easured shell abundances range from 2 to 23 specim ens per two-liter sam ple (n=86). Significant variability in shell breakage is observed betw een th ese sam ples (p<0.05). A verage epibiont p resen ce,estim ates for each sam ple range from 0% to 30% (n=9). M easured shell ab u n d an ces range from 2 to 23 specim ens per two-liter sam ple (n=86). Significant variability in epibiont p resen ce is not observed betw een th ese sam ples. Turritella carinata Eight sam ples of T. carinata (Fig. 17e) w ere collected from the Gosport and Lisbon Form ations at Little Stave C reek and the Tom bigbee River, respectively (Figs. 7,9). A verage shell breakage estim ates for each sam ple from the G osport range from 17% to 37% (n=6; Table 14). M easured shell a b u n d an ces range from 223 to 410 specim ens per two-liter sam ple (n=1694). Very highly significant variability in shell breakage is observed betw een th ese sam ples (p<0.001). A verage epibiont presence estim ates for each sam ple range from 4% to 22% (n=6). M easured shell ab u n d an ces range from 223 to 410 specim ens per two-liter sam ple (n=1694). Very highly significant variability in epibiont presence is observed betw een th ese sam ples (p<0.001). A verage shell breakage estim ates for each sam ple from the Lisbon range from 77% to 86% (n=2; Table 14). M easured shell ab u n d an ces range from 22 to 353 specim ens per two-liter sam ple (n=375). Significant variability in shell breakage is not observed betw een th ese sam ples. A verage epibiont p resen ce estim ates for each sam ple are 0% (n=2) and therefore do not exhibit 124 any variability. M easured shell abundances range from 22 to 353 specim ens per two-liter sam ple (n=375). Turritella fischeri Two sam ples of T. fischeri (Fig. 17f) were collected from the Moodys Branch Formation at Tcheva Creek (Fig. 12). No broken specim ens were found; therefore there w as no variance in shell breakage betw een sam ples. Average epibiont presence estim ates for each sam ple range from 0% to 25% (n=2; Table 14). M easured shell abundances range from 1 to 4 specim ens per two-liter sam ple (n=5). Significant variability in epibiont presence is not observed betw een th ese sam ples. Turritella ahiana Six sam ples of T. ghigna (Fig. 17g) were collected from the Gosport Sand at Little Stave Creek (Fig. 9). Average shell breakage estim ates for each sam ple range from 0% to 60% (n=6; Table 14). M easured shell abundances range from 1 to 11 specim ens per two-liter sam ple (n=45). Significant variability in shell breakage is not observed betw een th ese sam ples. Average epibiont presence estim ates for each sam ple range from 0% to 75% (n=6). M easured shell abundances range from 1 to 11 specim ens per two-liter sam ple (n=45). Significant variability in epibiont presence is observed betw een these sam ples (p<0.05). Turritella mississippiensis Twelve sam ples of T. mississippiensis (Fig. 17h) w ere collected from the Byram Formation at W est Talahalla Creek in Mississippi (Fig. 15). Average shell breakage estim ates for each sam ple range from 76%% to 92% (n=12; Table 14). M easured shell abundances range from 93 to 219 specim ens per 125 two-liter sam ple (n=1808). Highly significant variability in shell breakage is observed betw een th ese sam ples (p<0.01). Average epibiont presence estim ates for each sam ple range from 0% to 4% (n=12). M easured shell abundances range from 93 to 219 specim ens per two-liter sam ple (n=1808). Very highly significant variability in epibiont presence is observed betw een th ese sam ples (p<0.001). Turritella nasuta Five sam ples of T. nasuta (Fig. 17i) were collected from the Stone City B eds along the Brazos River. Average shell breakage estim ates for each sam ple range from 75% to 100% (n=5; Table 14). M easured shell abundances range from 21 to 186 specim ens per two-liter sam ple (n=284). Highly significant variability in shell breakage is observed betw een th ese sam ples (p<0.01). Average epibiont presence estim ates for each sam ple range from 0% to 18% (n-5). M easured shell abundances range from 21 to 186 specim ens per two-liter sam ple (n=284). Very highly significant variability in epibiont p resence is observed betw een th ese sam ples {p<0.001). Turritella obruta Five sam ples of T. obruta (Fig. 17j) were collected from the Gosport Sand at Little Stave Creek (Fig. 9). Average shell breakage estim ates for each sam ple range from 0% to 17% (n=5). M easured shell abundances range from 2 to 17 specim ens per two-liter sam ple (n=37). Significant variability in shell breakage is not observed betw een th ese sam ples. Average epibiont presence estim ates for each sam ple range from 25% to 50% (n=5). M easured shell abundances range from 2 to 17 specim ens per two-liter sam ple (n=37). 126 Significant variability in epibiont presence is not observed between these sam ples. Turritella perdita Seventeen sam ples of T. perdita (Fig. 17k) were collected from 3 outcrops of the Moodys Branch Formation at outcrops at the Chickasawhay River, LeFleur's Bluff, and Tcheva Creek in Mississippi (Figs. 11-13). Average shell breakage estim ates for each sam ple from the Chickasawhay River range from 79% to 92% (n=5; Table 14). M easured shell abundances range from 102 to 570 specim ens per two-liter sam ple (n=1481). Very highly significant variability in shell breakage is observed between these sam ples (p<0.001). Average epibiont presence estim ates for each sam ple range from 13% to 51% (n=5). M easured shell abundances range from 102 to 570 specim ens per two- liter sam ple (n=1481). Very highly significant variability in epibiont presence is observed betw een these sam ples (p<0.001). Average shell breakage estim ates for each sam ple from LeFleur's Bluff range from 57% to 65% (n=3; Table 14). Measured shell abundances range from 40 to 168 specim ens per two-liter sam ple (n=321). Significant variability in shell breakage is not observed between these sam ples. Average epibiont presence estim ates for each sam ple range from 1 % to 3% (n=3). Measured shell abundances range from 40 to 168 specim ens per two-liter sam ple (n=321). Significant variability in epibiont presence is not observed between these sam ples. Average shell breakage estim ates for each sam ple from Tcheva Creek range from 60% to 86% (n=9; Table 14). M easured shell abundances range from 28 to 335 per two-liter sam ple (n=1478). Very highly significant variability 127 in shell b reak ag e is observed betw een th ese sam p les (p<0.001). A verage epibiont p resen c e estim ates for each sam ple range from 2% to 33% (n=9). M easured shell a b u n d an c es range from 28 to 335 specim en s per two-liter sam ple (n=1478). Very highly significant variability in epibiont p resen c e is observed betw een th e s e sam ples (p<0.001). Summary Utilizing individual taxa, significant differences w ere noted betw een sam p les in both taphonom ic param eters (Table 9). A nalyses of epibiont p resen c e reveal significant variability betw een sam p les in 7 out of 16 taxa. Similarly, significant variability in shell b reakage is observed in 8 out of 16 taxa. Within S pecies: B etw een O utcrops S ev en teen two-liter sam p les w ere collected from th ree outcrops of the Moodys Branch Form ation at the C hickasaw hay River, T cheva C reek, and at LeFleur's Bluff in order to a s s e s s variability betw een different outcrops of the sa m e form ation (Figs. 11-13). T h ese outcrops have two sp e cie s of turritelline gastro p o d s which are com m on to b oth-T . alveata and T. perdita (Fig. 17d,k). A verage shell b reak ag e estim ates for T. alveata range from 76% to 86% (n=3; T able 10). M ean shell breakage estim ates for each outcrop a re b a se d on 9 sam p les at T cheva Creek, 5 at the C hickasaw hay River, and 3 at LeFleur’s Bluff. Significant variability in shell b reakage is not observed betw een th e se three outcrops . A verage epibiont p resen ce estim ates range from 7% to 31% (n=3; Table 10). M ean epibiont p resen c e estim ates for each outcrop are b ased on 9 128 sam p les at T cheva C reek, 5 at the C hickasaw hay River, and 3 at LeFleur's Bluff. Significant variability in m ean epibiont p resen ce is not observed betw een th e se three outcrops. A verage shell b reakage estim ates for T. perdita range from 60% to 83% (n=3; T able 10). M ean shell b reakage estim ates for each outcrop a re b a se d on 9 sam p les at T cheva C reek, 5 at the C hickasaw hay River, and 3 at LeFleur's Bluff. Highly significant variability in shell b reak ag e is observed betw een th e se th ree outcrops (p<0.01). A verage epibiont p resen c e estim ates range from 2% to 25% (n=3; Table 10). M ean epibiont p resen ce estim ates for each outcrop are b a se d on 9 sam p les at T cheva Creek, 5 at the C hickasaw hay River, and 3 at LeFleur's Bluff. Significant variability in m ean epibiont p resen c e is observed betw een th e se th ree outcrops (p<0.05). Summary Using individual taxa to a s s e s s variability, significant variability betw een outcrops of the sam e formation is observed in one out of two taxa (Table 11). Significant variability betw een outcrops is observed in both epibiont p resen c e and shell breakage param eters. Within S pecies: Betw een Form ations Four form ations from the sa m e epoch w ere com pared to o n e an o th er in order to a s s e s s variability betw een them . T h ese included the G osport, Lisbon, M oodys Branch, and S tone City Form ations (Fig. 3). Turritelline gastropod sp e c ie s com m on to the S tone City and Lisbon Form ations include M. 129 claibornensis (Fig. 17a). Turritelline gastropod sp ecies com m on to th e G osport and Lisbon Form ations include T. carinata (Fig. 17e). A verage shell b reakage estim ates for M. claibornensis range from 35% to 74% (n=2; T able 12). M ean shell breakage estim ates for each form ation are b a se d on 5 sam p les in the S tone City B eds and 2 sam p les in the Lisbon Form ation. Significant variability in m ean shell breakage is not observed betw een th e se 2 form ations. A verage epibiont p resen ce estim ates range from 1% to 9% (n=2; T able 12). M ean epibiont estim ates for each formation are b a sed on 5 sam p les in the S to n e City B eds and 2 sam p les in the Lisbon Form ation. Significant variability in m ean epibiont p resen c e is not observed betw een th e se 2 form ations. A verage shell breakage estim ates for T. carinata range from 29% to 81% (n=2; T able 12). M ean shell breakage estim ates for each formation a re b a se d on 6 sam p les in th e G osport Sand and 2 sam p les in the Lisbon Form ation. Very highly significant variability in m ean shell b reakage is observed betw een th e s e 2 form ations (p<0 .0 0 1 ). A verage epibiont p resen ce estim ates range from 0% to 11% (n=2; Table 12). M ean epibiont p resen c e estim ates for each formation are b ased on 6 sam p les in the G osport S and and 2 sam ples in the Lisbon Form ation. Significant variability in m ean epibiont p resen ce is not observed betw een th ese 2 form ations. 130 Summary Using individual tax a to a s s e s s variability betw een form ations of similar ag e, significant variability is observed in one of two tax a (Table 13). Significant variability is observed in shell b reakage param eters. Museum Collections B etw een S p e c ie s Variability T axa from each studied formation w ere com pared to o n e another in order to determ ine if betw een-species variability p o sed a significant so u rce of bias in m useum collections. T he sa m e taxa exam ined from field-based sam p les w ere analyzed in m useum collections. Only m useum sp ecim en s which cam e from the sam e outcrops studied in the fieid-based portion of this study w ere analyzed. T h ese included th e Gosport, Lisbon, Moodys Branch, and Stone City Form ations (Fig. 3). Lisbon Formation Lisbon Form ation sam p les from the M ississippi B ureau of G eology (hereafter MBG), th e A labam a Geological Survey (hereafter AGS), and the Los A ngeles County M useum of Natural History (hereafter LACMNH; T able 16) include several taxa of turritelline gastropods, including T. carinata and M. claibornensis (Fig. 17a,e). A verage length estim ates for th e s e taxa are 31.69 mm (n=41) and 27.31 mm (n=60), respectively (Table 17). Highly significant differences in m ean length estim ates are noted betw een th e se taxa (p<0 .0 1 ). M ean whorl diam eter estim ates for th e se two taxa are 9.25 mm (n=41) and 8.65 mm (n=62), respectively. Significant variability in whorl diam eter is not Taxon Form ation O utcrop M usuem Collection M ode # of S pecim en s M. claibornensis M oodys Branch R iverside Park 1 Bulk 4 M. claibornensis Stone City B razos River 5 Bulk 206 M. claibornensis Lisbon T om bigbee River 4 Bulk 88 M. vetusta G osport Little S tav e C reek 1 Bulk 8 M. vetusta G osport Little S tav e C reek 4 Bulk 519 T. apita G osport Little S tav e C reek 1 Bulk 3 T. apita G osport Little S tav e C reek 4 Bulk 20 T. alveata M oodys Branch Riverside Park 2 Bulk 2 T. carinata G osport Little S tav e C reek 1 Bulk 2 T. carinata G osport Little S tav e C reek 3 Bulk 130 T. carinata G osport Little S tav e C reek 4 Bulk - 5 T. carinata Lisbon Tom bigbee River 1 Bulk 13 T. carinata Lisbon Tom bigbee River 3 Bulk? 63 T. carinata Lisbon Tom bigbee River 4 Bulk 33 T. ghigna G osport Little S tav e C reek 1 Bulk 2 T. ghigna G osport Little S tav e C reek 4 Bulk 3 T. mississippiensis Byram T alahalia C reek 1 Bulk 10 T. nasuta G osport Little S tav e C reek 1 Bulk 4 T. nasuta Stone City B razos River 5 Bulk 484 T. nasuta Stone City B razos River 6 Bulk? 43 T. nasuta Lisbon T om bigbee River 3 Bulk? 41 T. nasuta Lisbon T om bigbee River 4 Bulk 180 T. nasuta Moodys Branch R iverside Park 1 Bulk 8 T. obntta G osport Little S tav e C reek 1 Bulk 4 T. obruta G osport Little S tav e C reek 4 Bulk 262 T. perdita Moodys Branch Riverside Park 1 Bulk 5 TOTALS: 10 6 5 6 n/a 2142 1 = M ississippi B ureau ol G eology 2 = L ouisiana S ta te University 3 = Los A ngeles County M useum of Natural History 4 = A labam a Geological Survey 5 = T ex as A & M | 6 = C. Thornton p ers. coll. T able 16: S am ple sizes, source, locality, and m ode of collection for m useum d a ta which w as com parable to study taxa. 132 # o f Specimens to in co ■ Mean % Bkn • 94.74% * ■ ' ■ ■ ' - 1 90.77% • ■ # o f Specimens C O 206 h* C O m C M C M C M O S o 23 © § 528 in !M ean % i Peel sS © C O C \ J ■ M - : 5.64% ■ 0.73% j 0.00% 158.33% i 39.62% 115.60% I 8.70% | i 10.00% 5.64% 8.52% 60.00%l # of I Specimens C O 0s - m O) in 206 137 in C M C M C M 8 r * 23 O T“ § C O C M in m § | a > c £ aS o © o 0.00% 0.00% 9.43% % 6om 0.00% 0.00% 5.64% £ m C O 0.00% 1 # o f Specimens s 206 137 m < M C M W o> © T* C O C M o 1 4E6 C O C M in in Mean % Drill 26.57% 27.67% a? o> o i & o o o 1 16.67% I f c u> o X T 24.77% 13.04% I % 0 0 '0 29.97% 1 S? C O 3 & 3 d c n c Q J o E * * s Q > O C O O i <0 r*- 1 C M 28 C O 1 h- Oi 00 • Mean B H Diam U m s o C M ' C O C M in n C M 3 ' o m © 154 I • #01 Specimens 6 2 | 3 ■»-* h - in C M 2 3 | O Oi Oi C O in Mean WD 1 8.65 I 4.81 C M rr o 17.98 C O © r*. © T ' tn w o> 2 7.03 | to d 8 o> 10.41 I # o f Specimens o < & | 1 5 4 | C O S3 C M 5 10 o 9 3 | m i Mean ! Length O J 15.01 | 28.41 | 10.39 | Oi C O ? C O C O 31.69 | 51.68 | tn C M Oi 05 c i T* iS a 34.54 I i ;Formallon c o a 3 Slone C itv 1 Gosport Gosport Moodys I Gosport I Lisbon I Gosport | B yram | £ o I D c C O Gosport | £ 8 E Taxon .V ) £ 8 S a C J 2= |M . c l a i b o r n e n s i s \ 3 s 5 ‘ to & T. a l v e a t a T. c a r i n a t a ■5 < u * l ■c Ol 8 •5 .1 l -ta e h* IT. n a s u t a f f l 3 o h » S ‘e £ ! ■ » T able 17: M ean values and sam ples sizes for m useum specim ens for all param eters. Size param eters are in mm. 133 observed betw een these two taxa. Mean drillhole diam eter estim ates for these taxa are 1.45 mm (n=28) and 1.72 mm (n=19), respectively. Significant variability in drillhole diam eter is not observed betw een th ese two taxa. Mean drilling intensity estim ates for th ese taxa are 25% (n=109) and 29% (n=84), respectively. Significant variability in drilling intensity is not observed betw een these two taxa. Mean drilling inefficiency estim ates for these taxa are 10% (n=109) and 6 % (n=84), respectively. Significant differences in drilling inefficiency are not noted betw een these two taxa. Mean peeling intensity estim ates for th ese taxa are 16% (n=109) and 43% (n=84), respectively. Very highly significant differences are noted in peeling intensity betw een these two taxa (p<0 .0 0 1 ). Gosoort Sand Gosport Sand sam ples com e from the MBG, LACMNH, and AGS {Table 16) and include a num ber of taxa of turritelline gastropods, including M. vetusta, T. apita, T. carinata, T. ghigna, and T. obruta (Fig. 17b,c,e,g,j). Average length estim ates for these taxa range from 18.39 mm to 51.68 mm and include analysis of a total of 52 individuals (Table 17). Very highly significant differences in m ean length are noted betw een these taxa (p<0.001). Mean whorl diam eter estim ates for th ese taxa range from 6.11 mm to 17.98 mm and include analysis of 52 individuals. Very highly significant differences in m ean whorl diam eter are noted betw een th ese taxa (p<0.001). Mean drillhole diam eter estim ates for th ese taxa (except T. ghigna) range from 1.25 mm to 2.27 mm and are based on analysis of 16 individuals. Significant differences in drillhole diam eter estim ates are observed betw een these taxa (p<0.05). Mean drilling intensity estim ates for th ese taxa range from 0% to 41 % and are based on analysis of 134 905 individuals. Very highly significant differences are noted in drilling intensity between these taxa {p<0.001). Mean drilling inefficiency estim ates range from 0% to 9% and are based on analysis of 905 individuals. Highly significant differences are noted in drilling inefficiency between these taxa (p<0.01). Mean peeling intensity estim ates for these taxa range from 0% to 40% and are based on analysis of 905 individuals. Very highly significant differences are noted in peeling intensity between these taxa (p<0 .0 0 1 ). Stone City Beds Sam ples of the Stone City Beds com e from Texas A & M (hereafter TAM) and the personal collections of Chuck Thornton (hereafter CT; Table 16) and include several taxa of turritelline gastropods, including M. claibornensis and T. nasuta (Fig. 17a,i). Mean length estim ates for these taxa are 15.01 mm (n=154) and 13.99 mm (n=93), respectively (Table 17). Significant differences in length are not noted between these taxa. Mean whorl diameter estim ates for these taxa are 4.81 mm (n=163) and 3.37 mm (n=99), respectively. Very highly significant differences in whorl diameter are noted between these two taxa (p<0.001). Mean drillhole diameter estim ates for these two taxa are 0.78 mm (n=76) and 0.59 mm (n=97), respectively. Highly significant differences in drillhole diam eter are noted between these taxa (p<0.01). Mean drilling intensity estim ates for these two taxa are 28% (n=206) and 30% (n=337), respectively. Significant differences in drilling intensity are not noted between these taxa. Mean drilling inefficiency estim ates for these taxa are 13% (n=206) and 6 % (n=337), respectively. Highly significant differences in drilling inefficiency are noted between these taxa (p<0.01). Mean peeling intensity estim ates for these taxa are 51% (n=206) and 42% (n=337), respectively. 135 Significant differences in peeling intensity are noted between these taxa (p<0.05). Mean shell breakage estim ates for these taxa are 95% (n=57) and 91% (n=65), respectively. Significant differences in shell breakage are not noted between these taxa. Moodys Branch Formation Moodys Branch Formation sam ples come from Louisiana State University {hereafter LSU) and MBG (Table 16) and include two taxa of turritelline gastropods, including T. alveata and T. perdita (Fig. 17d,k). Mean length estim ates for these two taxa are 39.41 mm (n=12) and 34.54 mm (n=5), respectively (Table 17). Significant differences in length are not noted between these taxa. Mean whorl diameter estim ates for these taxa are 10.18 mm (n=12) and 10.41 mm (n=5), respectively. Significant differences in whorl diam eter are not noted betw een these taxa. Between-species com parisons of drillhole diam eter and drilling inefficiency estim ates are not m ade because only one of these taxa contains evidence of drilling activity. Mean drilling intensity estim ates for these taxa are 17% (n=12) and 0% (n=5), respectively. Significant differences in drilling intensity are not observed between these taxa. Mean peeling intensity estim ates for these taxa are 58% (n=12) and 60% (n=5), respectively. Significant differences in peeling intensity are not observed between these taxa. Summary Significant variability between constituent taxa is observed in three out of four studied formations examined from museum collections (Table 18). Significant variability is observed in all studied param eters except for shell 136 Formation Length Max WD BH Diam % Drill % Ineff % Peel % Bkn Lisbon 0.007 0.090 0.090 0.550 0.300 0.000 - Gosport 0.000 0.000 0.010 0.000 0.003 0.000 - Stone City 0.420 0.000 0.004 0.570 0.002 0.030 0.410 Moodys 0.240 0.810 - 0.360 1.000 0.950 - T able 18: P -values for b etw een -sp ecies com parisons in m useum collections. 137 b reak ag e (but note that shell b reakage w as only exam ined in one m useum collection). Lisbon Form ation sam p les exhibit variability in two of th e six studied p aram eters, and G osport and S tone City Form ation sam p les exhibit significant variability in six out of six and four out of six param eters, respectively. Studied O utcrops vs. M useum Collections: Mixed S p ecies M eans M ixed-species formation "averages" w ere calculated for each formation (for e ac h study param eter) by combining a v erag e s for constituent taxa. Four form ations from the sa m e epoch contained m ore than one taxon of turritelline gastropod and could be com pared to the field-based d ata (hereafter labeled "study specim ens") b a se d on m ixed-species a v e ra g e s for th e studied p aram eters. T h e se included th e Gosport, Lisbon, M oodys Branch, and S tone City Form ations (Fig. 3, T able 16). Lisbon Formation Lisbon Form ation m useum sam ple m ea n s are b ased on synthesis of m ean values for two constituent turritelline taxa. M ean length values for m useum specim en s (29.50 mm) exhibit significant differences (p<0.05) from m ean length estim ates for study specim ens (8.10 mm; T able 19). M ean whorl diam eter estim ates for m useum specim ens (8.95 mm) exhibit significant differences (p<0.05) from m ean whorl diam eter estim ates for study sp ecim en s (2.97 mm). M ean drillhole diam eter estim ates for m useum sp ecim en s (1.59 mm) do not exhibit significant differences from m ean drillhole diam eter estim ates for study specim ens (0.80 mm). M ean drilling intensities for m useum sp ecim en s (27% ) do not exhibit significant differences from drilling intensities for study specim ens (26%). M ean drilling inefficiency estim ates for m useum 138 Formation Source S o t T axa Length Max WO BH Diam % Drill % Ineff % P eel % Bkn G osport M useum 5 34.33 10.80 1.77 16.07% 3.59% 11.51% Outcrop 5 12.42 4.16 1.05 10.57% 3.85% 24.61% Lisbon M useum 2 29.50 8.95 1.59 26.67% 8.02% 29,23% Outcrop 2 8.10 2.97 0.60 25.57% 4.86% 11.32% Moodys Branch M useum 2 3G.9B 10.30 2.28 8.33% 0.00% 59.17% Outcrop 2 19.03 5.27 0.90 5.49% 0.64% 39.75% S to n e City M useum 2 14.50 4.09 0.69 28.82% 9.37% 46.80% 92.75% Outcrop 2 8.66 3.30 0.77 15.21% 0.23% 16.57% 86.49% T able 19: M ixed-species values and sam ple sizes of com parable m useum and outcrop specim ens. 139 specim ens (8 %) do not exhibit significant differences from drilling inefficiencies for study specim ens (5%). Mean peeling intensity estim ates for m useum specim ens (29%) do not exhibit significant differences from peeling intensity estim ates for study specim ens (1 1%). Gosport Sand G osport Sand m useum sam ple m eans are based on synthesis of m ean values for five constituent turritelline taxa. Mean length values for m useum specim ens (34.33 mm) exhibit highly significant differences (p<0.01) from m ean length estim ates for study specim ens (12.42 mm; Table 19). Mean whorl diam eter estim ates for m useum specim ens (10.80 mm) exhibit significant differences (p<0.05) from m ean whorl diam eter estim ates for study specim ens (4.16 mm). M ean drillhole diam eter estim ates for m useum specim ens (1.77 mm) exhibit significant differences (p<0.05) from m ean drillhole estim ates for study specim ens (1.05 mm). Mean drilling intensity estim ates for m useum specim ens (16%) do not exhibit significant differences from m ean drilling intensity estim ates for study specim ens (11%). M ean drilling inefficiency estim ates for m useum specim ens (4%) do not exhibit significant differences from m ean drilling inefficiency estim ates for study specim ens (4%). Mean peeling intensity estim ates for m useum specim ens (12%) do not exhibit significant differences from m ean peeling intensity estim ates for study specim ens (25%). Stone Citv Beds Museum sam ple m eans for the Stone City B eds are based on a synthesis of m ean values for two constituent turritelline taxa. Mean length values for m useum specim ens (14.50 mm) exhibit significant differences 140 (p<0.05) from m ean length estim ates for study specim ens (8 .6 6 mm; Table 19). Mean whorl diam eter estim ates for m useum specim ens (4.09 mm) do not exhibit significant differences from m ean whorl diam eter estim ates for study specim ens (3.30 mm). Mean drillhole diam eter estim ates for m useum specim ens (0.69 mm) do not exhibit significant differences from m ean drillhole diam eter estim ates for study specim ens (0.77 mm). Mean drilling intensity estim ates for m useum specim ens (29%) do not exhibit significant differences from m ean drilling intensity estim ates for study specim ens (15%). Mean drilling inefficiency estim ates for m useum specim ens (9%) do not exhibit significant differences from m ean drilling inefficiency estim ates for study specim ens (<1%). Mean peeling intensity estim ates for m useum specim ens (47%) exhibit significant differences (p<0.05) from m ean peeling intensity estim ates for study specim ens (17%). Mean shell breakage estim ates for m useum specim ens (93%) do not exhibit significant differences from m ean shell breakage estim ates for study specim ens (8 6 %). Mood vs Branch Formation Moodys Branch Formation m useum sam ple m eans are based on synthesis of m ean values for two constituent turritelline taxa. Mean length values for m useum specim ens (19.03 mm) do not exhibit significant differences from m ean length estim ates for study specim ens (36.98 mm; Table 19). Mean whorl diam eter estim ates for m useum specim ens (5.27 mm) do not exhibit significant differences from m ean whorl diam eter estim ates for study specim ens (10.30 mm). Lack of multiple specim ens m akes analysis of variability betw een data sources (for drillhole diameter) impossible. Mean drilling intensity estim ates for m useum specim ens (5%) do not exhibit significant differences 141 from m ean drilling intensity estim ates for study specim ens (8 %). Mean drilling inefficiency estim ates for museum specim ens (1%) do not exhibit significant differences from m ean drilling inefficiency estim ates for study specim ens (0 %). Mean peeling intensity estim ates for museum specim ens (40%) do not exhibit significant differences from m ean peeling intensity estim ates for study specim ens (59%). Summary When utilizing mixed-species sam ple m eans to analyze formation-level differences between museum- and field-based data sets, significant variability is observed in three of the four formations (Table 20). Significant variability is only observed in predator and prey size param eters. Significant variability is observed between Lisbon Formation data sources in two of the six studied param eters. Similarly, significant variability between data sources is observed in three of six and one of seven param eters in the Gosport and Stone City Formations, respectively. Studied Outcrops vs. Museum Collections: Within Species Means The studied outcrops were also compared to museum collections by utilizing results from individual taxa. Within species m eans were calculated for each taxon (for each study parameter) by analyzing all of the individuals found in museum collections or in the studied outcrops. Twelve taxa from five different formations (Lisbon, Gosport, Stone City, Moodys Branch, and Byram Formations) were comparable to those found in the studied outcrops (Table 16). 142 Formation Length Max WD BH Diam % Drill % Ineff % Peel % Bkn Gosport 0.020 0.020 0.080 0.950 0.590 0.380 - Lisbon 0.005 0.010 0.040 0.450 0.930 0.390 . M oodys Branch 0.040 0.630 0.750 0.250 0.130 0.046 0.220 Stone City 0.230 0.160 - 0.800 0.420 0.550 - Table 20: P-values for comparison of m ixed-species results of com parable museum and outcrop specim ens. 143 Mesafia claibornensis. Lisbon Formation Mean shell length estim ates for M. claibornensis (Fig. 17a) from the Lisbon Formation are 17.06 mm in study specim ens (n=52) and 27.1 mm in museum specim ens (n=60; Tables 17,21). Very highly significant differences in m ean shell length are noted between these two sources of data (p<0 ,0 0 1 ). Mean whorl diam eter estim ates are 6.31 mm for study specim ens (n=55) and 8.65 mm for m useum specim ens (n=62). Very highly significant differences in m ean whorl diam eter are noted between these data sources {p<0.001). Mean drillhole diam eter estim ates are 1.25 mm for study specim ens (n=26) and 1.72 mm for m useum specim ens (n=19). Highly significant differences in m ean drillhole diam eter are noted between these data sources (p<0.05). Mean drilling intensity estim ates are 36% for study specim ens (n=55) and 29% for m useum specim ens (n=84). Significant differences in m ean drilling intensities are not observed between these data sources. Mean drilling inefficiency estim ates are 18% for study specim ens (n=55) and 6 % for museum specim ens (n=84). Significant differences in m ean drilling inefficiency estim ates are observed between these data sources (p<0.05). Mean peeling intensity estim ates are 38% for study specim ens (n=55) and 43% for museum specim ens (n=84). Significant differences in m ean peeling intensity are not observed between these data sources. Mesalia claibornensis. Stone City Beds Mean shell length estim ates for M. claibornensis (Fig. 17a) from the Stone City Beds are 8 .6 6 mm for study specim ens (n=62) and 15.01 mm for museum specim ens (n=154; Tables 17,21). Very highly significant differences 144 HOI Specimens • C M • ■ • ■ ■ * • 3 C M 3 ■ Mean% I Bkn • ^ .p O' $ id C O ■ £ 5 > s? $ £ - U e a > ’ o E s v> S g s C O C M to 3 C O T* fG C O in ■ M - g C O 3 C M S T * C M W M ean % Peel 1 C D n 5 C O C M 3 cd o' 8 d V ? O' 8 o C O C O S ' 8 id a? S d C M IS C M C M £ 3 C M g 3 C O C M a? o m d T * #of Specimens in in g C Q C M in s co £ p > in - M - eo © C O r- 3 C M 01 O C M C O M ean % Ineff. e£ C Q a> 1 d £ £ s o & S o I £ E d C M in ^ T £ 8 d SS in o> 1 d I H O f | Specimens in in C D o S C O C M m a C O 15 03 g C O 3 C M s Y- 8 Mean% | Drill sS 10 C D to C O ■ k O O' C O C O M - £ o c m O' C T 5 C O eo •v? S ' o o d a? O) N tri vO § T* £ v5 S ' in C M in as m a> £ C O to ** V * vO S ' cn ■n d #0f I Specimens' C O C M m g o o C O o n * * cn C M in V- » #0f BH Specimens Diam & 3 (O C O d g * — 878 I 0 .9 5 s r* h* in 1694 ! 0 .7 5 375 1 2 .1 4 • in Tf oo o C O ■ » — in C M a C M to C O o 3 C O i a ci a 5 > C O C O in 8 c i 3 to s 3 C M C M C O m C O C M m C M 8 t} - 8 c m ' # o f i Specimens C M m C M C O co 5 s in 7.23 i 1489 I 6.74 i 290 I 3 C O o a? C O C M O) C O C O o eo rt o eo C M c £ 3 C 2 3 C O o C O C O 03 in o eo C O d 3 0) C M 3 to cd o > C O Formation c o £ 1 C D □ & O 0 ) c o 55 ■ e o a 8 C P tr & « o (D £ *o o o 2 t: o a s c o o 3 tr a o (3 E 2 >> 03 iStone C ity 1 cr o £2 3 e X) g S Taxon I Af. claibornensis \ \M. claibornensis I s 3 S 5 £5 & t-; ■ S s Q h? 1 s h: ja 1 3 h i c a ,& 5 " B j 42 S - Q ) .1 V ) y> $ £ 0 3 ra C O cr h -’ S 5 •Q ta § s f-: Table 21: Within-species m eans and sam ple sizes for formations based on outcrop data. Size param eters in mm. 145 in m ean shell length are observed between these data sources (p<0 .0 0 1 ). Mean whorl diameter estim ates are 4.51 mm for study specim ens (n=109) and 4.81 mm for museum specim ens (n=163). Significant differences in m ean whorl diam eter estim ates are not observed between these data sources. Mean drillhole diam eter estim ates are 0.86 mm for study specim ens (n=15) and 0.78 mm for museum specim ens (n=76). Significant differences in m ean drillhole diam eter estim ates are not observed between these data sources. Mean drilling intensity estim ates are 15% for study specim ens (n=109) and 28% for m useum specim ens (n=206). Highly significant differences in drilling intensity estim ates are observed between these data sources (p<0.01). Mean drilling inefficiency estim ates are 1% for study specim ens (n=109) and 13% for museum specim ens (n=206). Very highly significant differences in m ean drilling inefficiency are observed between these data sources (p<0.001). Mean peeling intensity estim ates are 27% for study specim ens (n=109) and 51% for museum specim ens (n=206). Very highly significant differences in mean peeling estim ates are observed between these data sources (p<0.001). Mean shell breakage estim ates are 85% for study specim ens (n=124) and 95% for museum specim ens (n=57). Very highly significant differences in m ean shell breakage estim ates are observed between these data sources (p<0 .0 0 1 ). Mesalia vetusta. Gosport Sand Mean shell length estim ates for M. vetusta (Fig. 17b) from the Gosport Sand are 10.25 mm for study specim ens (n=816) and 28.41 mm for museum specim ens (n=13; Tables 17,21). Very highly significant differences in m ean length estim ates are observed between these data sources (p<0.001). Mean whorl diam eter estim ates are 3.88 mm for study specim ens (n=878) and 9.33 146 mm for m useum specim ens (n=13). Very highly significant differences in m ean whorl diam eter are noted betw een th ese d ata so u rces (p<0.001). M ean drillhole diam eter estim ates are 0.95 mm for study specim ens (n=128) and 1.24 mm for m useum sp ecim en s (n=8 ). Significant differences in m ean drillhole diam eter are not observed betw een th e se d ata sources. M ean drilling intensity estim ates are 12% for study specim ens (n=878) and 17% for m useum sp ecim en s (n=528). Highly significant differences in m ean drilling intensity are observed betw een th e s e two d ata so u rces (p<0.01). M ean drilling inefficiency estim ates a re 5% for study specim ens (n=878) and 9% for m useum specim ens (n=528). Highly significant differences in m ean drilling inefficiency a re noted betw een th e s e d a ta so u rces (p<0.01). M ean peeling intensity estim ates are 8 % for study sp ecim en s (n=878) and 9% for m useum specim en s (n=528). Significant differences in peeling intensity are not observed betw een th e s e d ata so u rces. Turritella apita. Gosport Sand M ean shell length estim ates for T. apita (Fig. 17c) from th e G osport Sand are 16.38 mm for study specim ens (n=7) and 18.39 mm for m useum specim ens (n=23; T ables 17,21). Significant differences in m ean length estim ates a re not observed betw een th e se d ata sources. M ean whorl diam eter estim ates a re 6.50 mm for study specim ens (n=9) and 6.10 mm for m useum sp ecim en s (n=23). Significant differences in m ean whorl diam eter are not observed betw een th e se d ata sources. M ean drillhole diam eter estim ates are 1.34 mm for study sp ecim en s (n=1) and 1.24 mm for m useum specim en s (n=3). Significant differences in m ean drillhole diam eter are not observed betw een th e se d ata sources. M ean drilling intensity estim ates are 8 % for study 147 specim ens (n=1 2 ) and 13% for m useum specim ens (n=23). Significant differences in m ean drilling intensity are not observed betw een th ese two data sources. M ean drilling inefficiency estim ates are 0% for study specim ens (n=12) and 0% for m useum specim ens (n=23). Thus, there are no differences in m ean drilling inefficiency betw een th ese two d ata sources. Mean peeling intensity estim ates are 0% for study specim ens (n=12) and 9% for m useum specim ens (n=23). Significant differences in peeling intensity are not observed betw een th e se data sources. Turritella alveata. Moodvs Branch Formation M ean shell length estim ates for T. alveata (Fig 17d) from the Moodys Branch Formation are 29.34 mm for study specim ens (n=5) and 39.42 mm for m useum specim ens (n=12; T ables 17,21). Significant differences in m ean length estim ates are observed betw een th ese data so u rces (p<0.05). Mean whorl diam eter estim ates are 7.74 mm for study specim ens (n=5) and 10.18 mm for m useum specim ens (n=12). Significant differences in m ean whorl diam eter are observed betw een th ese data sources (p<0.05). Mean drillhole diam eter estim ates are not calculated b ecau se there are no drilled specim ens in one of the two data sources. Mean drilling intensity estim ates are 0% for study specim ens (n=5) and 17% for m useum specim ens (n=12). Significant differences in m ean drilling intensity are not observed betw een th ese two data sources. M ean drilling inefficiency estim ates are 0% for both outcrop and m useum specim ens and therefore exhibit no differences. M ean peeling intensity estim ates are 60% for study specim ens (n=5) and 58% for m useum specim ens (n=12). Significant differences in peeling intensity are not observed betw een th ese data sources. 148 Turritella carinata. Gosport Sand Mean shell length estim ates for T. carinata (Fig. 17e) from the Gosport Sand are 7.23 mm for study specim ens (n=1489) and 38.44 mm for m useum specim ens (n=7; Tables 17,21). Very highly significant differences in m ean length estim ates are observed betw een th ese data sources (p<0.001). Mean whorl diam eter estim ates are 2.65 mm for study specim ens (n=1694) and 10.41 mm for m useum specim ens (n=7). Very highly significant differences in m ean whorl diam eter are observed betw een th ese d ata sources (p<0.001). Mean drillhole diam eter estim ates are 0.75 mm for study specim ens (n=106) and 2.27 mm for m useum specim ens (n=4). Very highly significant differences in m ean drillhole diam eter are observed betw een these data sources {p<0.001). Mean drilling intensity estim ates are 6 % for study specim ens (n=1694) and 9% for m useum specim ens (n=137). Significant differences in m ean drilling intensity are not observed betw een these two data sources. Mean drilling inefficiency estim ates are 1% for study specim ens (n=1694) and 0% for m useum specim ens (n=137). Significant differences in m ean drilling inefficiency are not observed betw een th ese two data sources. Mean peeling intensity estim ates are 6 % for study specim ens (n=1694) and 1% for m useum specim ens (n=137). Highly significant differences in peeling intensity are observed betw een th ese data sources (p<0 .0 1 ). Turritella carinata. Lisbon Formation Mean shell length estim ates for T. carinata (Fig. 17e) from the Lisbon Formation are 6.74 mm for study specim ens (n=290) and 31.68 mm for m useum specim ens (n=41; Tables 17,21). Very highly significant differences in m ean length estim ates are observed betw een these data sources (p<0.001). Mean 149 whorl diam eter estim ates are 2.14 mm for study specim ens (n=375) and 9.25 mm for m useum specim ens (n=41). Very highly significant differences in m ean whorl diam eter are observed betw een these data sources (p<0.001). Mean drillhole diam eter estim ates are 0.63 mm for study specim ens (n=43) and 1.45 mm for m useum specim ens (n=28). Very highly significant differences in m ean drillhole diam eter are observed betw een these data sources {p<0.001). Mean drilling intensity estim ates are 11 % for study specim ens (n=375) and 25% for m useum specim ens (n=109). Very highly significant differences in m ean drilling intensity are observed betw een these two data sources (p<0 .0 0 1 ). Mean drilling inefficiency estim ates are 1% for study specim ens (n=375) and 10% for m useum specim ens (n=109). Very highly significant differences in m ean drilling inefficiency are observed betw een th ese two data sources {p<0.001). Mean peeling intensity estim ates are 5% for study specim ens (n=375) and 16% for m useum specim ens (n=109). Highly significant differences in peeling intensity are observed betw een th ese data sources (p<0 .0 1 ). Turritella ahiana. Gosport Sand Mean shell length estim ates for T. ghigna (Fig. 17g) from the Gosport Sand are 10.81 mm for study specim ens (n=44) and 51.68 mm for m useum specim ens (n=5; Tables 17,21). Very highly significant differences in m ean length estim ates are observed betw een these data sources (p<0.001). Mean whorl diam eter estim ates are 3.72 mm for study specim ens (n=45) and 17.98 mm for m useum specim ens (n=5). Very highly significant differences in m ean whorl diam eter are observed betw een th ese data sources (p<0.001). Drillholes w ere only present in one of the data sources— hence com parisons of drillhole 150 diam eters are not m ade. M ean drilling intensity estim ates are 11% for study specim ens (n=45) and 0% for m useum specim ens (n=5). Significant differences in m ean drilling intensity a re not observed betw een th e s e two data so u rces. M ean drilling inefficiency estim ates are 2 % for study specim ens (n=45) and 0% for m useum specim ens (n=5). Significant differences in m ean drilling inefficiency are not observed betw een th e se two d ata so u rces. M ean peeling intensity estim ates are 20% for study specim ens (n=45) and 0% for m useum sp ecim en s (n=5). Significant differences in peeling intensity are not o bserved betw een th e s e d ata sources. Turritella mississippiensis. Bvram Formation M ean shell length estim ates for T. mississippiensis (Fig. 17h) from the Byram Form ation are 8.39 mm for study specim ens (n=1288) and 25.28 mm for m useum specim en s (n-10; T ables 17,21). Very highly significant differences in m ean length estim ates are observed betw een th e se d a ta so u rces (p<0 .0 0 1 ). M ean whorl diam eter estim ates are 2.85 mm for study specim en s (n=1808) and 7.03 mm for m useum specim ens (n=10). Very highly significant differences in m ean whorl diam eter are observed betw een th e se d ata so u rces (p<0 .0 0 1 ). Drillholes w ere only present in one of the d ata so urces--hence com parisons of drillhole diam eters are not m ade. M ean drilling intensity estim ates a re 5% for study sp ecim en s (n=1808) and 0 % for m useum specim ens (n=1 0 ). Significant differences in m ean drilling intensity are not observed betw een th e s e two d ata so u rces. M ean drilling inefficiency estim ates a re <1% for study sp ecim en s (n=1808) and 0% for m useum specim ens (n=10). Significant differences in m ean drilling inefficiency are not observed betw een th e se two d a ta sources. M ean peeling intensity estim ates are 2% for study specim en s (n=1808) and 151 10% for m useum specim ens (n=10). Significant differences in peeling intensity are not observed betw een th e se d ata sources. Turritella nasuta. Stone Citv Beds M ean shell length estim ates for T. nasuta (Fig. 17i) from the S tone City B eds are 7.64 mm for study specim ens (n=183) and 13.99 mm for m useum sp ecim en s <n=93; T ables 17,21). Very highly significant differences in m ean length estim ates are observed betw een th e se d ata so u rces (p<0.001). M ean whorl diam eter estim ates are 2.15 mm for study specim ens (n=284) and 3.37 mm for m useum sp ecim en s (n=99). Very highly significant differences in m ean whorl diam eter a re observed betw een th e se d ata so u rces (p<0.001). M ean drillhole diam eter estim ates are 0.63 mm for study specim en s (n=29) and 0.59 mm for m useum sp ecim en s (n=97). Significant differences in m ean drillhole d iam eter a re not observed betw een th e se d ata sources. M ean drilling intensity e stim ates a re 9% for study specim ens (n=284) and 30% for m useum specim en s (n=337). Very highly significant differences in m ean drilling intensity are ob serv ed betw een th e se two d ata so u rces (p<0.001). M ean drilling inefficiency estim ates are 1 % for study specim ens (n=284) and 6 % for m useum specim en s (n=337). Very highly significant differences in m ean drilling inefficiency are ob serv ed betw een th e se two d ata so u rces (p<0.001). M ean peeling intensity estim ates are 13% for study specim ens (n=284) and 42% for m useum sp ecim en s (n=337). Very highly significant differences in peeling intensity are ob serv ed betw een th e se d a ta so u rces (p<0.001). M ean shell b reakage estim ates are 92% for study specim ens (n=284) and 91% for m useum sp ecim en s (n=59). Significant differences in m ean shell b reak ag e are not observed betw een th e se two d ata sources. 152 Turritella obruta. Gosport Sand Mean shell length estim ates for T. obruta (Fig. 17j) from the Gosport Sand are 13.61 mm for study specim ens (n=31) and 34.75 mm for m useum specim ens (n=4; tables 17,21). Very highly significant differences in m ean length estim ates are observed betw een th ese data sources (p<0 .0 0 1 ). Mean whorl diam eter estim ates are 4.40 mm for study specim ens (n=37) and 10.17 mm for m useum specim ens (n=4). Very highly significant differences in m ean whorl diam eter are observed between these data sources (p<0.001). Mean drillhole diam eter estim ates are 1.19 mm for study specim ens (n=3) and 2.35 mm for m useum specim ens (n=1). Significant differences in m ean drillhole diam eter are not observed betw een th ese data sources. Mean drilling intensity estim ates are 11% for study specim ens (n=37) and 41% for m useum specim ens (n=212). Very highly significant differences in m ean drilling intensity are observed betw een th ese two data sources (p<0.001). Mean drilling inefficiency estim ates are 0% for study specim ens (n=37) and 9% for m useum specim ens (n=2 1 2 ). Significant differences in m ean drilling inefficiency are not observed betw een these two data sources. Mean peeling intensity estim ates are 24% for study specim ens (n=37) and 39% for m useum specim ens (n=212). Significant differences in peeling intensity are not observed betw een th ese data sources. Turritella perdita. Moodvs Branch Formation Mean shell length estim ates for 7. perdita (Fig. 17k) from the Moodys Branch Formation are 7.89 mm for study specim ens (n=280) and 34.54 mm for m useum specim ens (n=5; Tables 17,21). Very highly significant differences in m ean length estim ates are observed betw een th ese data sources (p<0 .0 0 1 ). M ean whorl diam eter estim ates are 2.53 mm for study specim ens (n=394) and 153 10.41 mm for museum specim ens (n=5). Very highly significant differences in m ean whorl diam eter are observed between these data sources (p<0 .0 0 1 ). Drillholes were only present in one of the data sources--hence comparisons of drillhole diam eters are not made. Mean drilling intensity estim ates are 11% for study specim ens (n=321) and 0 % for museum specim ens (n=5). Significant differences in m ean drilling intensity are not observed between these two data sources. Mean drilling inefficiency estim ates are 2 % for study specim ens (n=321) and 0% for museum specim ens (n=5). Significant differences in mean drilling inefficiency are not observed between these two data sources. Mean peeling intensity estim ates are 11% for study specim ens (n=321) and 60% for museum specim ens (n=5). Very highly significant differences in peeling intensity are observed between these data sources (p<0 .0 0 1 ). Summary Utilizing individual taxa, significant differences between museum- and field-based data sets are observed in all of the studied param eters (Table 22). Significant variability between data sources is observed in 11 out of 12 studied taxa. Table 22: P-values for within-species comparisons o f museum and outcrop data. Taxon Formation Mean Length Mean WD Mean BH Diam Mean % D rill Mean % Ineff. Mean % Peel Mean % Bkn M. claibornensis Lisbon 0.000 0.000 0.005 0.340 0.020 0.590 - M. claibornensis Stone City 0.000 0.390 0.530 0.009 0.000 0.000 0.072 M. vetusta Gosport 0.000 0.000 0.060 0.007 0.002 0.950 - T, apita Gosport 0.620 0.730 0.910 0.690 1.000 0.310 - T. alveata Moodys 0.020 0.030 - 0.360 1.000 0.950 - T. carinata Gosport 0.000 0.000 0.000 0.080 0.240 0.008 - T. carinata Lisbon 0.000 0.000 0.000 0.000 0.000 0.001 - T. ghigna I Gosport 0.000 0.000 - 0.440 0.740 0.280 - T. mississippiensis Byram 0.000 0.000 - 0.460 0.860 0.100 - T . nasuta Stone City 0.000 0.000 0.620 0.000 0.001 0.000 0.766 T. obruta Lisbon 0.000 0.000 0.070 0.001 0.050 0.090 - T. perdita \ Moodys 0.000 0.000 - 0.440 0.750 0.001 - 154 155 DISCUSSION In the preceeding section, lateral variability has been identified at several sc ale s by analyzing ch an g es in the characteristics of turritelline gastropod assem b lag es. In this section, th ese results are analyzed in order to a s s e s s the probability of encountering sampling artifacts a s a result of this variability, and to a s s e s s effects of this variability on larger-scale predation studies. Sm all-scale patterns of variability are analyzed first, and are followed by analysis of variability at increasingly larger scales. Sam ples collected in this study are subsequently com pared to m useum collections and to results reported in the literature in order to a sse ss: i) potential b iases in utilizing th e se data sources; and ii) effects of lateral variability on large-scale predation studies. S uggestions for ch an g es in sam pling strategies are m ade, in part b ased on identification of potential c a u se s for lateral variability in th e studied outcrops. Within-Sample Variability W ithin-sample variability com pares differences observed betw een different species from the sam e sam ples. Analysis of variability is very important at this small scale, b ecau se it is at this scale in which potential biases betw een species m ay be identified. This type of analysis elucidates w hether significant differences (in size, abundance, etc.) might exist betw een different sp ecies in a sam ple. If significant differences do exist, then larger-scale observations might need to consider th ese differences by analyzing patterns within (one or more) individual species rather than combining all species. At the S tone City Beds locality, four of five sam ples exhibit significant variability betw een taxa in at least one of the eight m easured param eters. Two 156 sam ples exhibit significant variability in one of the param eters, one sam ple exhibits significant variability in three of the param eters, and one sam ple exhibits significant variability in four of the param eters. Estim ates of prey size exhibit significant variability between species in the study sam ples. O ne out of five sam ples exhibit significant variability in length w hereas four out of five sam ples exhibit significant variability in whorl diameter. Based on whorl diam eter results, significant differences exist between constituent species in alm ost all (80%) of the studied sam ples. Thus, if large-scale studies of predation utilize whorl diam eter to estim ate prey size, they m ay need to exam ine constituent taxa individually, in order to avoid biases [like those indicated in i), ii) and iii) of the Methods section] resulting from combining values for constituent taxa which have different abundances. Estim ates of drilling intensity, epibiont presence, and shell breakage all exhibit significant variability betw een species in one sam ple. Estim ates of predator size and drilling inefficiency do not exhibit any significant variability betw een constituent species (within a given sam ple). B ased on the num ber of sam ples and param eters used in this study, these results suggest that there is a 23% probability of encountering statistically significant variability betw een constituent taxa in any studied sam ple from this outcrop of the Stone City Beds. At the Lisbon Formation locality, both of the sam ples exhibit significant variability in at least two of the param eters. O ne sam ple exhibits highly significant variability in all eight of the m easured param eters. All param eters except drilling intensity exhibit significant variability betw een species in at least one of the m easured param eters. Significant variability in drilling intensity is noted betw een species in both sam ples from this outcrop. T hese results 157 indicate that significant variability exists in all sam ples collected from this outcrop and that collection of multiple (>2 ) sam ples and separation of constituent taxa may be necessary. Based on the number of sam ples and param eters used in this study, there is a 6 6 % probability of encountering statistically significant variability between constituent taxa in any studied sam ple from this outcrop of the Lisbon Formation. At the Gosport Sand locality, all of the six sam ples exhibit significant variability in at least two of the param eters. One sam ple exhibits variability in three of the param eters and four of the sam ples exhibit variability in five of the param eters. All param eters (except whorl diameter) exhibit significant variability between species in at least one of the sam ples. Prey size characteristics exhibit significant variability between species in all of the studied sam ples. Drilling and peeling intensity each exhibit significant variability between species in two of the studied sam ples. Study of taphonomic characteristics indicates significant variability exists between species in four sam ples. These results suggest that significant variability exists in all sam ples collected from this outcrop (in the majority of studied param eters) and that collection of multiple (>2 ) sam ples and separation of constituent taxa may be necessary. Based on the number of sam ples and param eters used in this study, there is a 52% probability of encountering statistically significant variability between constituent taxa in any studied sample from this outcrop of the Gosport Sand. At the Moodys Branch Formation locality at Tcheva Creek, seven of the nine sam ples exhibit significant variability in at least one of the param eters. One sam ple exhibits variability in one of the param eters, another in two 158 param eters, two sam ples exhibit variability in three of the param eters, two sam ples exhibit variability in four of the param eters, and one sam ple exhibits variability in five of the param eters. All param eters except drilling intensity and epibiont presence exhibit significant variability in at least one of the sam ples. Prey characteristics and peeling intensity all exhibit significant variability in six sam ples, whorl diam eter exhibits significant variability in two of the sam ples, and drilling inefficiency and shell breakage exhibit significant variability in one of the sam ples. Based on the number of sam ples and param eters used in this study, there is a 31% probability of encountering statistically significant variability between constituent taxa in any studied sam ple from this outcrop. T hese results suggest that collection of multiple (>2) sam ples and separation of constituent taxa may be necessary. At the Moodys Branch Formation at LeFleur's Bluff, all three sam ples exhibit significant variability in at least two of the param eters. Two sam ples exhibit variability in three of the study param eters. All param eters except drilling intensity, drilling inefficiency, and shell breakage exhibit significant variability in at least one of the sam ples. Whorl diam eter and peeling intensity estim ates exhibit variability in two sam ples each, w hereas length estim ates exhibit variability in all three sam ples. Based on the number of sam ples and param eters used in this study, there is a 38% probability of encountering statistically significant variability between constituent taxa in any studied sam ple from this outcrop. Thus, these results suggest that collection of multiple sam ples and separation of constituent taxa may be necessary. At the Moodys Branch Formation at the Chickasawhay River, four of five sam ples exhibit significant variability in at least two of the studied param eters. 159 One sam ple exhibits significant variability in three of the param eters and one sam ple exhibits significant variability in four of the param eters. All param eters except drilling and peeling intensity exhibit significant variability in at least one of the studied param eters. Shell length and whorl diameter estim ates exhibit significant variability in three and four (respectively) of the sam ples. Based on the num ber of sam ples and param eters used in this study, there is a 28% probability of encountering statistically significant variability between constituent taxa in any studied sample from this outcrop. Thus, these results suggest that collection of multiple sam ples and separation of constituent taxa may be necessary. Synthesis of all of the information from the three outcrops of the Moodys Branch Formation suggests that there is a 32% probability of encountering statistically significant variability between constituent taxa in any given sample, regardless which one of these param eters is studied. This suggests that the likelihood of encountering a sam ple which requires separation of constituent taxa is high. In order to avoid this potential bias, one should collect multiple sam ples and/or separate constituent taxa. Between-Sample Variability Results of within-sample variability indicate that significant variability between different species occurs in most sam ples. This variabiiity suggests that examination of larger-scale patterns of lateral variability would benefit from isolation of individual taxa within each sample (i.e., "within species" or within "constituent" taxa). Examination of individual taxa aids in constraining sources of variability and allows this study to more accurately identify small-scale 160 variability in sam ples (particularly if variability in one taxon might have been hom ogenized by variability in another). For comparison, however, it is useful to also analyze variability at larger scales using one combined species average from each sam ple (i.e., "mixed species"). Mixed S pecies Of the six outcrops analyzed in this study, half of them exhibit significant variability betw een sam ples in at least one param eter. The Gosport and Lisbon Formation outcrops and the LeFleur's Bluff outcrop of the Moodys Branch Formation do not exhibit any significant lateral variability betw een sam ples (in any param eter) when constituent species m eans are combined. B ased on this m ethod of calculating sam ple averages and considering the num ber of sam ples used in this study, there is a 6 % probability of encountering statistically significant variability betw een sam ples at any outcrop or param eter utilized in this study. Within Species Mesalia claibornensis occurs in two formations (the Lisbon and Stone City) and only exhibits significant variability betw een sam ples from the former. Significant variability is observed in three of the eight study param eters, including length, whorl diameter, and shell breakage estim ates. B ased on the num ber of sam ples and param eters used in this study, there is a 19% probability of encountering significant variability betw een sam ples at both outcrops. In the Stone City outcrop, there is no likelihood of encountering significant variability, w hereas there is a 38% probability in the Lisbon outcrop. 161 M. vetusta from the Gosport Sand exhibits significant variability in four of the eight study param eters, including size param eters, drilling inefficiency, and shell breakage. B ased on this information there is a 50% probability of encountering significant variability betw een sam ples in any given study param eter. Turritella apita occurs in very low abundance at the studied outcrop of the Gosport Sand and does not exhibit any significant variability betw een sam ples in any of the study param eters. Generalizations about the likelihood of encountering significant variability betw een sam ples should not be m ade until larger num bers of sam ples are collected. T. alveata occurs in three different outcrops of the Moodys Branch Formation and exhibits significant variability in at least three param eters at two of the three localities. Significant variability betw een sam ples is observed in size param eters at two outcrops, w hereas significant variability betw een sam ples in drilling epibiont presence and shell breakage is observed at one outcrop. B ased on the num ber of sam ples and param eters used in this study, there is a 26% probability of encountering significant variability betw een sam ples at all three outcrops. At the LeFleur's Bluff outcrop there is no likelihood of encountering significant variability, w hereas there is a 38% probability at the Tcheva Creek and Chickasawhay River outcrops. Extremely small num bers of T. alveata at this locality suggest that this suggested lack of variability may not be significant-larger num bers of specim ens and sam ple sizes will better elucidate potentially significant variability. T. carinata occurs in two different formations (Lisbon and Gosport) and only exhibits significant variability betw een sam ples at the latter. Significant 162 variability is observed in four of the eight m easured param eters, including size param eters, epibiont presence, and shell breakage. Based on the num ber of sam ples and param eters used in this study, there is a 25% probability of encountering significant variability between sam ples at both outcrops. At the outcrop in the Gosport Sand, there is a 50% likelihood of encountering variability, w hereas at the Lisbon Formation, there is no likelihood of encountering variability. However, the small number of sam ples collected at the Lisbon Formation outcrop may ham per accurate identification of variability in T. carinata--hence, collection of larger numbers of specim ens and sam ple sizes will better elucidate significant patterns of variability. T. fischeri occurs in very low abundance at one outcrop of the Moodys Branch Formation and does not exhibit any significant variability between sam ples in any of the study param eters. Thus, generalizations about the likelihood of encountering significant variability between sam ples should not be m ade until larger num bers of sam ples are collected. T. ghigna occurs at one outcrop of the Gosport Sand and only exhibits significant variability between sam ples in one param eter, epibiont presence. Based on the num ber of sam ples and param eters used in this study, there is a 14% probability of encountering significant variability between sam ples of T. ghigna at this outcrop. T. mississippiensis occurs at one outcrop of the Byram Formation and exhibits significant variability between sam ples in all of the studied param eters except drilling inefficiency and peeling intensity (for which p=0.05). Analysis of this taxon is extremely robust because of large num bers of sam ples at the study outcrop and high abundances of specim ens in each sample. Based on the 163 number of sam ples and param eters used in this study, there is a 75% probability of encountering significant variability between sam ples of T. mississippiensis at this outcrop. T. nasuta occurs at one outcrop of the Stone City Beds and exhibits significant variability between sam ples in four of the eight study param eters, including size param eters, epibiont presence, and shell breakage. Based on the num ber of sam ples and param eters used in this study, there is a 50% probability of encountering significant variability between sam ples of T. nasuta at this outcrop. T. obruta occurs in very low abundance at one outcrop of the Gosport Sand and does not exhibit any significant variability between sam ples in any of the study param eters. Thus, generalizations about the likelihood of encountering significant variability between sam ples should not be m ade until larger num bers of sam ples are collected. T. perdita occurs at three outcrops of the Stone City Beds and exhibits significant variability in at least four param eters at each outcrop. Significant variability between sam ples is observed in six out of eight param eters at the Tcheva Creek locality and in seven out of eight param eters at the Chickasawhay River locality. Significant variability between sam ples is observed in all three outcrops in size and peeling intensity param eters. Significant variability between sam ples is observed in two outcrops in drilling intensity, epibiont presence, and shell breakage estim ates. Whorl diam eter and drilling inefficiency each exhibit significant variability in one of the three studied outcrops. Based on the number of sam ples and param eters used in this study, there is a 71% probability of encountering significant variability between 164 sam ples at all three outcrops. At the LeFleur's Bluff outcrop there is at 50% probability of encountering significant variability between sam ples, w hereas there is a 75% probability at the Tcheva Creek outcrop and an 8 8 % probability at the Chickasawhay River outcrop. Between-Outcrop Variability Mixed Species By analyzing each param eter (for each outcrop of the Moodys Branch Formation) individually, significant variability between outcrops is only observed in one param eter, epibiont presence. Based on this method of calculating outcrop m eans for each param eter, there is a 13% probability of encountering significant variability between studied outcrops, regardless of which study param eter is examined. Comparison of this level of probability with the 32% probability calculated from analysis of all individual sam ples (see above) suggests that this may represent a minimum estim ate of between-outcrop variability in the Moodys Branch Formation and that more information (i.e., more sam ples and outcrops) is necessary to better constrain this estimate. Within Species Analysis of individual param eter averages (for each outcrop) suggests that significant variability between outcrops does not exist in 7 * . alveata, but is present in four of the m easured param eters in T. perdita, including whorl diameter, drilling intensity, epibiont presence, and shell breakage. Thus, based on these results, there is no likelihood of encountering significant between- 165 outcrop variability in T. afveata. In T. perdita, however, there is a 50% probability of encountering significant variability betw een outcrops, suggesting th e necessity to collect sam ples from multiple outcrops w hen studying this taxa. Between-Formation Variability Mixed S p e c ie s By analyzing each p aram eter (for all sam ples from each outcrop) individually, significant variability betw een form ations is observed in th ree of eight p aram eters, including drilling intensity, epibiont p resen ce, and shell break ag e. B ased on this m ethod of calculating sam ple m ea n s for all outcrops of each formation, th ere is a 38% probability of encountering significant variability betw een studied form ations, regardless of which study p aram eter is exam ined. Within S p ecies Exam ination of sam ple m ean s for all m easured p aram eters su g g e sts that significant betw een-form ation variability d o es not exist in M. claibornensis (note, how ever, that near-significant variability is observed in drilling intensity; p=0.05). In T. carinata, how ever, significant variability betw een form ations is observ ed in th ree of eight param eters, including whorl diam eter, drillhole diam eter, and shell breakage. B ased on this m ethod of analyzing sam ple m eans, th ere is a low likelihood of encountering significant betw een-form ation variability in M. claibornensis, w h ereas there is a 38% probability of encountering betw een- formation variability in T. carinata. 166 Variability in Different Modes of Data Synthesis and in Different Parameters Betw een S am ples For all studied outcrops, there is a 6 % probability of encountering betw een-sam ple variability (when mixed species m eans are used for each sam ple). However, the sam e type of analysis (using individual taxa m eans from each sam ple) su g g ests that there is a 35% chance of encountering significant betw een-sam ple variability. T h ese levels of betw een-sam ple lateral variability are not beyond the realm of statistical significance (i.e., p < 0.05) and suggest that this type of lateral variability is pervasive enough to merit collection of multiple sam ples at th ese outcrops and/or identification of sources of variability. In addition, th e se results suggest that there is a much higher likelihood of identifying th e so u rces of lateral variability (e.g., highly variable param eters, taxa, or sam ples) at each outcrop by analyzing sam ples in which the m ean s of the constituent taxa have been differentiated. Of all the studied param eters, prey size param eters have the highest probability (65%) of encountering significant betw een-sam ple variability. Most of th e se sam ples exhibit extrem ely highly significant levels of betw een-sam ple variability (p « 0 .0 0 1 ). Taphonom tc characteristics are also characterized by high probability (44%) of encountering significant betw een-sam ple variability. Predator size, drilling and peeling intensity, and inefficiency estim ates are all characterized by low levels of variability. Som e taxa, such as T. perdita and T. mississippiensis, are highly affected by betw een-sam ple lateral variability (probabilities = 71% and 75%, 167 respectively). Taxa such a s T. nasuta and M. vetusta may be moderately affected by betw een-sam ple lateral variability {probabilities = 50%). Other taxa exam ined in this study exhibit much lower levels of betw een-sam ple lateral variability. T hese results suggest that the processes which affect lateral variability at the study outcrops m ost strongly influence specim en size and quality of preservation. Estim ates of predatory activity are not affected a s strongly by patterns of lateral variability. Small num bers of taxa, small num bers of individuals, and small num bers of sam ples can ham per the identification of between-outcrop lateral variability in this study because they decrease the precision of analyses of variance (Alder and R oessler, 1977). To analyze these potential biases, all m ixed-species patterns of variability were also analyzed after removing sam ples with th ese biases (i.e., small sam ple size, etc.). Most sam ples in this study are characterized by small num bers of turritelline taxa (i.e., <5 taxa). Lumping of individual taxa m eans together (to obtain one sam ple m ean) may thus hinder accurate detection of patterns of betw een-sam ple lateral variability. Differences in the accuracy of recognition of patterns of lateral variability have been dem onstrated betw een the two m ethods of d ata synthesis in this study (see above). Significant differences (p < 0.001) exist betw een usage of individual-taxa m eans and mixed-taxa m eans to analyze betw een-sam ple variability. As previously noted, this indicates the need to identify patterns of lateral variability based on individual taxa. Six sam ples of the studied taxa are characterized by abundances which might potentially be so small (i.e., < 25 individuals/sample) that they may hinder 168 identification of significant betw een-sam ple variability. After removal of these specim ens, significant betw een-sam ple lateral variability is observed in at least three param eters in 9 of 11 taxa. Significant betw een-sam ple variability is observed in all of the studied param eters, with half of the taxa exhibiting significant betw een-sam ple variability in at least half of the param eters. Based on th ese results, there is a 45% probability of encountering significant betw een- sam ple variability in any given taxon or param eter. Two sam ples of the studied taxa are characterized by sam ple sizes which might potentially be so small (i.e., <3 sam ples/taxa) that they may hinder identification of significant betw een-sam ple variability. After removal of these specim ens, significant betw een-sam ple lateral variability is observed in at least one param eter in 10 of 14 taxa. Significant betw een-sam ple variability is observed in all of the studied param eters, with half of the taxa exhibiting significant variability in at least half of the param eters. B ased on th ese results, there is a 40% probability of encountering significant betw een-sam ple variability in any given taxa or param eter. Betw een-sam ple variability w as also analyzed after removal of both sam ples with few individuals and taxa with few sam ples. This eliminates eight potentially biased taxa. After removal of th ese specim ens, significant between- sam ple variability is observed in at least three param eters in 8 of 9 taxa. Significant betw een-sam ple variability is observed in all of the studied param eters, with half of the taxa exhibiting significant variability in at least half of the param eters. Based on th ese results, there is a 53% probability of encountering significant betw een-sam ple variability in any given taxon or param eter. 169 In sum, the large sam ples from well-sampled outcrops suggest that between-sam ple variability is pervasive among the studied taxa and param eters. Probabilities of encountering this type of (Type I) sampling error (as a result of collection of a non-representative sample) may be greater than 50%. Prey size and shell preservation param eters are most strongly affected by betw een-sam ple lateral variability in all m ethods of data analysis utilized in this study. Between Outcrops Comparison of between-outcrop variability based on mixed-taxa m eans for each sam ple versus variability estim ates based on individual-taxa m eans indicates that the latter has the potential for better identification of lateral variability. The probability of identifying significant between-outcrop variability is almost 13% higher when utilizing the latter method. Separation of constituent taxa m eans indicates that all of the significant variability occurs in only one of the two taxa analyzed from the Moodys Branch Formation. Like betw een-sam ple variability, removal of potentially biasing sam ples increases the probability of identifying significant variability within the studied taxa. For example, removal of sam ples with small num bers of individuals increases the probability of encountering significant variability from 31% to 50%. Removal of outcrops with small numbers of sam ples does not affect the likelihood of encountering between-outcrop variability. 170 Betw een Form ations C om parison of betw een-form ation variability b a sed on m ixed-taxa m ea n s for each sam ple versus variability estim ates b a sed on individual taxa produces confusing results. Unlike com parisons of th e s e m ethods (of d ata synthesis) at other scales, m ixed-taxa m ean s yield higher levels of variability than m odes of analysis b ased on individual taxa. However, analysis of the two similar constituent taxa from th e se form ations indicates that different taxa are m aking significantly different contributions to different p aram eters, and hence, m ea su re s of betw een-form ation variability. This partly stem s from the fact that in the m ixed-taxa analysis, variance in all four form ations can be analyzed independently, w h ereas in an aly ses of individual taxa, only two of the form ations can be analyzed at a given time. In this c a se , estim ates of variance for M. ciaibornensis are b ased on outcrops of the S tone City B eds and the Lisbon Form ation, w h ereas an aly ses of T. carinata a re b a sed on outcrops of the G osport and Lisbon Form ations. Unlike betw een-sam ple and betw een-outcrop variability, rem oval of potentially biasing sam p les do es not ch an g e the probability of identifying significant variability within the studied taxa. This is largely due to th e fact that rem oval of potentially biasing sam p les from the betw een-form ation analysis of variability elim inates one of the two form ations and m ak es betw een-form ation analysis im possible. Drilling Predation: Ternary D iagram s As indicated in the M ethods section, previous large-scale predation studies have synthesized d ata in three different w ays, including: i) averaging all 171 specim ens together (combining different numbers of different species) to obtain a m ean for the interval under study; ii) averaging all species together, with each species within a sam ple contributing equally to the sam ple mean, regardless of abundance of different taxa; and iit) assessing each species independently. As also indicated above, this study only employs the latter two methodologies in order to avoid biases inherent in homogenization of information from disparate taxa. As has been illustrated above in tabular format, study results (utilizing the latter two m ethods above) clearly indicate pervasive lateral variability in all of the studied param eters, taxa, and at all scales. Predation characteristics, however, exhibit the lowest levels of variability observed in this study. Thus, it may be necessary to employ additional data synthesis techniques in order to identify lateral variability in predation characteristics. In order to m ake this further assessm ent of predation variability, a third method [i) from above] of data synthesis is employed. Unlike the rest of this study's results, which can be concisely synthesized in tabular format, the interdependence of m easured drilling predation param eters m akes them am enable to presentation in graphical format. Thus, drilling intensity and drilling efficiency are compared to one another in ternary- style diagrams which illustrate the range of values observed at different scales analyzed in this study. At the corners of the diagrams are: i) undrilled shells; it) efficiently drilled shells, including the fraction of all shells which are characterized by a single, complete drillhole; and iii) inefficiently drilled shells, including the fraction of shells which contain multiple or incomplete drilling attempts. 172 At present, information plotted in ternary diagrams is restricted to qualitative analyses because one cannot conduct a three-way analysis of variance for dependent triparate data. In addition, because of the nature of the studied characteristics (i.e., presence/absence of incomplete, multiple, or single complete drillholes), there is no experimental error which can be used to plot error bars on ternary diagrams. However, the range of values presented at correspondingly smaller scales can be inferred to represent the range of potential values obtainable from an outrop sample, and hence are a proxy for error bars (e.g., a cloud containing all of the standard deviations from the mean value of each data point). For example, the range of values displayed by individual taxa from each sample might be a good proxy for the range of values which might be expected to surround the m ean value for each sample. With these constraints in mind, lateral variability is examined in drilling predation characteristics at a variety of scales, including: i) between taxa; ii) between samples; iii) between outcrops; iv) between formations; and v) between epochs. At each scale, all individuals are averaged together (regardless of taxonomic identity or abundance) to obtain a m ean value for that taxon, sample, outcrop, formation, or epoch. Mean values for each epoch are first presented separately at each scale in order to avoid obscurement of data points by overlapping values. Because of the large number of points in these plots, subsequent composite ternary diagrams are presented in color. Individual taxa from each Eocene sample exhibit a wide range of variability in drilling frequency and presence of inefficiently drilled shells (range: - 1 0 0%), but indicate a range of - 2 0 % in presence of efficiently drilled shells (Fig. 18). The majority (>95%) of points are located in the upper third of the 0. 0 Efficiently Drilled Undrilled 0 Taxon Mean 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 Inefficiently Drilled Figure 18: Mean values for each taxa from each sample taken from Eocene outcrops utilized in this study. 174 diagram , indicating that m ost shells are undrilled, but when drilled, are drilled successfully. Individual sam ples from each E ocene outcrop exhibit a much sm aller range of values, with all values falling in the upper fifth of th e ternary diagram (Fig. 19). Sam ple m eans a re also com pared to the outcrop m ean for the one Oligocene outcrop utilized in this study and exhibit a similar pattern (Fig. 20). M ean values for each outcrop and formation (including E ocene and O ligocene outcrops) exhibit an alm ost identical range in values (Figs. 21 and 2 2 ) and su g g est that differences resulting from synthesis of all individuals are not distinguishable at th e se scales. Epoch m eans for all E ocene and Oligocene specim ens also cluster very closely together, in the upper tenth of the ternary diagram (Fig. 23). Com posite color plots of results from E ocene and Oligocene strata better identify th e se patterns (Fig. 24). Although m ost points in the sm aller-scale plots fall in the upper portions of the ternary diagram s, one can s e e that there is a large d eg ree of variability (as illustrated in the scatter of the points) which is not accounted for in the m ean values for each epoch. Thus, although variability in predation has been illustrated to be the lowest of all the studied param eters [i.e., via d ata synthesis m ethods ii) and iii) discussed in the M ethods section], there stili exists enough variability betw een constituent taxa and sam ples that if multiple sam ples w ere not collected, the risk of collecting a non-representative sam ple is high enough to merit consideration w hen devising sam pling strategies. Undrilled 0 Sample Mean 0.9 0.2 0.8 0.3 0.7 0.4 0.6 0.5 0.5 0.6 0.4 0.7 0.3 0.8 0.2 0.9 Inefficiently Drilled Efficiently Drilled Figure 19: Mean values for each sample taken from Eocene outcrops. Undrilled Q.1 0.9 o Sample Mean 0 Outcrop Mean 0.7 0.4 0.5 0.6 0.7 0.3 0.2 0.9 Inefficiently Drilled Efficiently Drilled Figure 20: Mean values for each sample from Oligocene strata. Because only one Oligocene outcrop was studied (the Byram Fm. at Talahalia Ck.), the outcrop mean is the sam e value as the formation and epoch means for this interval. Additionally, because only one taxon is present at this localtiy, between-taxa variations are not examined. Talahalla Ck Little Stave Ck. 0.8 Efficiently Drilled Chickasawhay R. Tcheva Ck. LeFleur’s Bl. Brazos R. Tombigbee R. Q Outcrop Mean Undriled 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0 .1 Inefficiently 0 Drilled Figure 21: Means for each outcrop utilized in this study (including Middle Eocene to Lower Oligocene strata). Efficiently Drilled Undrilled Byram „ Moodys Branch 1 - Stone City 0.2 r Lisbon \ 0.3 Gosport 0.9 0.8 0.7 0 Formation Mean 0.4 0.6 0.5 0.5 0.6 0.4 0.7 0.3 0.8 0.2 0.9 0 0 Inefficiently Drilled Figure 22: Means values for each formation utilized in this study. Efficiently Drilled Undrilled Oligocene 0.9 Eocene 0.2 0.8 0.3 Q Epoch Mean 0.7 0.4 0.6 0.5 0.5 0.6 0.4 0.7 0.3 0.8 0.2 0.9 0.1 f X X X X X X X X X Inefficiently 1 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0 .1 0 Drilled Figure 23: Mean values for each epoch analyzed in this study. Efficiently Drilled Undriiled Taxon Mean 0.9 0.2 Sample Mean Outcrop Mean Formation Mean 0.8 0.3 0.7 0.4 0.6 Epoch Mean 0.5 0.5 0.6 0.4 0.7 0.3 0.8 0.2 0.9 Q 0 Inefficiently Drilled Figure 24: Composite ternary diagram illustrating mean values from all studied samples, including Eocene and Oligocene data. 181 Museum Collections W ithin-Form ation Variability W ithin-formation variability co m p ares differences observed betw een different sp e c ie s from th e sa m e formation. Analysis of variability in m useum collections is sim ilar to within-sam ple variability in the studied outcrops b e c a u se it is at this scale in which potential b ia se s betw een sp e cie s m ay be identified. This type of analysis elucidates w hether significant differences (in size, ab u n d an ce, etc.) might exist betw een different sp ecies in a given form ation. If significant differences do exist, then larger-scale observations might n e ed to consider th e s e differences by analyzing patterns within (one or more) individual sp e cie s rather than combining all taxa. In th e Lisbon Form ation, highly significant differences betw een th e two constituent turritelline taxa are observed in two of the six param eters. In the G osport Sand, significant differences betw een the five constituent tax a are noted in all of the six param eters. In the Stone City B eds, significant differences betw een the two constituent taxa are observed in four of the seven param eters. In the M oodys Branch Formation, significant differences are not observed betw een th e two constituent taxa in any of the studied param eters. Exam ination of all the four studied form ations indicates that significant betw een-taxa differences exist in all of the studied param eters except shell breakage. B ased on the m useum collections and param eters u sed in this study, th ere is a 50% probability of encountering statistically significant differences betw een constituent taxa in any m useum -based sam ple of th e se form ations. 182 Museum- vs. Outcrop-Based Results Results of within-formation variability indicate that significant differences exist betw een different species from the sam e formation. T hese differences (observed in m useum collections) are similar to within-sample variability noted in outcrop-based sam ples. T hese results suggest that examination of larger- scale differences betw een m useum - and outcrop-based results would benefit from isolation of individual taxa within each formation. This aids in constraining sources of differences and allows this study to more accurately identify small- scale variability in m useum collections (particularly if characteristics of one taxon might be hom ogenized by characteristics of another). For comparison, however, it is useful to also analyze differences betw een th ese two sources of data (i.e. m useum - and field-based) at larger scales using m ixed-species averages for each formation. Comparison of Mixed Species Results Of the four formations which contained more than one taxon, three of them exhibit significant differences betw een m useum -based and field-based results. Significant differences are observed betw een th ese two data sources in at least two param eters in both the Lisbon and Gosport Formations and in one param eter in the Stone City Beds. The only param eters in which significant differences betw een data sources are identified are in shell length, whorl diam eter, and drillhole diameter. Based on this method of calculating formation averages and based on the param eters used in this study, there is a 25% 183 probability of encountering significant differences between these two data sources in any given formation or studied parameter. Comparison of Within Species Results All but one of the 12 turritelline taxa examined from the studied outcrops and m useum collections exhibit significant differences between the two data sources in at least two of the studied param eters. One taxon exhibits significant differences between data sources in six of the studied param eters, two taxa exhibit significant differences in five of the studied param eters, three taxa exhibit significant differences in four of the param eters, two taxa exhibit significant differences in three of the param eters, and three of the taxa exhibit significant differences in two of the studied param eters. Significant differences between data sources are observed in all of the studied param eters. Differences between data sources are most commonly observed in prey size param eters {with significant differences noted in 21 of 24 observations), including shell length and whorl diameter. Based on this method of calculating species averages and based on the param eters used in this study, there is a 56% probability of encountering significant differences between data sources in any given taxon or parameter. Removal of the two taxa which contain small {<25) num bers of individuals (T. apita and T. alveata) increases the likelihood of encountering significant differences between data sources in any given taxon or parameter. The likelihood of encountering significant differences in the remaining abundant taxa is 63%. 184 Variability in Different Modes of Data Synthesis and in Different Parameters Like results of within-sample variability (based on field samples), results of within-formation variability (based on museum samples) indicate the need to examine data sources based on mixed species averages arid individual species averages. Comparison of mixed taxa averages for museum and field data sources indicates that significant differences exist in most formations, with most differences occurring in prey size parameters. Comparison of individual taxa averages for museum and field data sources indicates that significant differences exist in most taxa, with differences occurring in all studied parameters. Individual taxa results also indicate that most differences are concentrated in prey size parameters. Although this pilot study only analyzes a limited number of taxa from 5 different formations, these results suggest that significant differences exist between m useum -based information and field-based information. Like most field-based results, most of the differences between data sources are centered around prey size characteristics. These differences suggest that shell populations extracted from museum collections may not represent shell populations collected from bulk sampling of outcrops. If this lack of representation affects levels of predator-prey interactions (via size-selective predation, etc.) then this may have significant effects upon large-scale studies which utilize museum collections as a data source. Although taphonomic characteristics were noted in field-based data sets, they were not noted in museum collections; thus, it is unknown if these characteristics are also strongly "biased" in museum collections (meaning characterized by high likelihood of 185 encountering a Type I, or sam pling, error). In sum , th e se preliminary results su g g e st that caution should b e u sed w hen utilizing m useum -based information to infer larger-scale patterns or to m ake paleobiological or paleoecological interpretations, particularly w hen size and possibly taphonom ic characteristics are involved. Study Variability and Published Results In order to help constrain results reported in large-scale studies of predation, their results a re directly com pared to results from this study (hereafter term ed "study" results). This com parison will also help to a s s e s s the effects of different sam pling strateg ies and d ata analysis techniques on results reported in large-scale studies of predation. R esults from this study a re used to aid large-scale predation studies by com paring sim ilar taxa from th e sa m e outcrops u sed in this field-based study. In order to m ake statistical com parisons betw een the study and literature d a ta so u rces, several potentially-biasing factors need to be taken into consideration: i) for large-scale predation studies which indicate th e standard deviations or variances for their results (Allmon et al., 1990), standard independent t-tests can be em ployed; and ii) for predation studies which do not publish stan d ard deviations or variances (Dudley and Vermeij, 1978; Kelley and H ansen, 1993), one m ust a ssu m e that the variance in th e literature-based results is z e ro -th u s, in com parisons betw een literature and study results, th e se published results a re assu m e d to represent the "true" m ean and a two-tailed t- te st is em ployed; and iii) all populations are assu m ed to be normally distributed. 186 Literature results and com parable study results are sum m arized in Table 23, including estim ates of sam ple sizes, m eans, and standard deviations. In order to m ake com parisons betw een study results and literature results, study specim ens were analyzed in the sam e m anner a s literature specim ens. Four of the studied param eters are utilized in direct com parisons, including prey size, drilling intensity, drilling efficiency, and peeling intensity. In com parisons of drilling and peeling intensity, all study specim ens were analyzed a s a group by combining specim ens from all study sam ples [following protocols of Dudley and Vermeij (1978) and Allmon et al. (1990)]. In com parisons of drilling efficiency, the num ber of unsuccessfully drilled shells is divided by the total num ber of successfully and unsuccessfully drilled shells (following protocols of Kelley and H ansen, 1993). Prey Size Param eters Com parisons of size betw een different data sources is a useful test to se e if both sources have extracted sam ples from the sam e shell populations. Although size distributions of studied taxa are often reported in large-scale predation studies (e.g., Adegoke and Tevesz, 1974; Dudley and Vermeij, 1978; Vermeij et al., 1980; Vermeij, 1987; Allmon et al., 1990; Kelley and Hansen, 1993; Tull and Bohning-Gaese, 1993), size distributions of individual taxa are often reported in abbreviated form and hence could not be used for direct com parisons. However, a study of an exceptionally preserved turritelline- dom inated shell bed from Mississippi (Allmon and Dockery, 1992) allows size com parisons to be m ade. Sam ples of the Lower Oligocene Byram Formation are dom inated by T. mississippiensis. Allmon and Dockery (1992) report a Table 23: Mean values, samples sizes, and sources o f information used fro m literature reports. Taxa Formation Site Source # of Specim ens Mean Length (mm) Drilling % Peeling % % Efficiency M. vetusta Gosport AL Kelley & Hansen 11 - - - 36.40% T. alveata Moodys Branch MS Allmon et al. 15 • 13.00% 90.00% - T. alveata Moodys Branch LA, MS Kelley & Hansen 26 - - - 7.70% T. carinata Gosport AL Allmon et al. 30 . 13.00% 20.00% - T. carinata Lisbon AL Kelley & Hansen 9 - - - 88.90% T. mississippiensis Byram MS Allmon et al. 30 . 3.00% 30.00% - T. mississippiensis Byram MS Allmon & Dockery 234 14.00 - . - T. nasuta Lisbon AL Kelley & Hansen 23 . - - 26.10% T. perdita Moodys Branch MS Allmon et al. 30 . 7.00% 10.00% . T. perdita Moodys Branch MS Dudley & Vermeij 70 . 21.00% - - infaunal gastropods Moodys Branch LA, MS Kelley & Hansen 49 - - - 3.04% infaunal gastropods Gosport AL Kelley & Hansen 17 - . - 11.80% infaunal gastropods Byram MS Kelley & Hansen 14 - - - 0.00% infaunal gastropods Cook Mountain AL Kelley & Hansen 443 - - - 3.80% 187 188 m ean length of -1 4 mm for T. mississippiensis, based on a sam ple of 234 individuals. A m ean length of 8.39 mm was observed in this study, based on 12 bulk sam ples totaling 1288 individuals. Very highly significant differences are noted between these two data sources ( p « 0 .0 0 1 ) and likely result from sample transport biases in this study. In particular, many of the larger (but very fragile) T. mississippiensis shells were likely broken during sam ple transport (e.g., Flessa et al., 1992). Predation Param eters Com parisons of predation param eters, including drilling intensity, efficiency, and peeling intensity, can be m ade between this study and published results and provide a direct m eans of assessing potential differences and potential biases inherent in different methods of sam ple collection. Of the studied taxa, six can be directly compared to similar taxa reported upon in large-scale predation studies. T hese include M. vetusta, T. alveata, T. carinata, T. mississippiensis, T. nasuta, and T. perdita. These taxa have been analyzed for predation param eters which are comparable to those utilized in this study, including drilling intensity (Dudley and Vermeij, 1978; Allmon et al., 1990), drilling efficiency (Kelley and Hansen, 1993), and peeling intensity (Allmon et al., 1990). Sam ples were collected at the sam e outcrops utilized in this study, and in the som e cases, such as the Byram Formation exposure on Talahalla Creek, from the sam e exact horizon. 189 Drilling Intensity Reported drilling intensity upon com parable specim ens of T. alveata is -1 3 % (n=15; Allmon et al., 1990) w hereas study results su g g est intensities of 0% (n=5). Significant differences betw een th ese two data sources a re not observed. Reported drilling intensity upon T. carinata is -1 3 % (n=30; Allmon et al., 1990) w hereas study results suggest intensities of - 6 % (n=1694). Very highly significant differences ( p « 0 .0 0 1 ) are observed betw een th e se data sources. Reported drilling intensity upon T. mississippiensis is -3 % (n=30) w hereas study results sug g est intensities of -5% (n=1808). Very highly significant differences (p<0 .0 0 1 ) are observed betw een th e se d ata sources. Reported drilling intensities on T. perdita are -7 % and -21 % (n=30, Allmon et al., 1990; n=70, Dudley and Vermeij, 1978; respectively) w hereas study results su g g est intensities of - 1 1% (n=321). Significant and very highly significant differences (p<0.05, p<0.001, respectively) are observed betw een th e se data sources. In addition to com parisons betw een individual taxa, com parisons can be m ade betw een reported levels of drilling predation for entire epochs. For exam ple, Allmon et al. (1990) suggest drilling intensities of -23% for the E ocene (n=436 specim ens, n=12 taxa) w hereas study results su g g est drilling intensities of -7 % (n=4421 specim ens, n=10 taxa). **Very highly significant differences (p<0 .0 0 1 ) are observed betw een drilling intensity estim ates from th e se d ata sources. Allmon et al. (1990) also suggest drilling intensities of - 2 % for th e Oligocene (n=45 specim ens, n=2 taxa) w hereas study results sug g est drilling intensities of -5 % (n=1808 specim ens, n=1 taxa). Very highly significant 190 differences (p<0 .0 0 1 ) are observed betw een drilling intensity estim ates from th e se d ata sources. In sum , taxon-to taxon com parisons of drilling intensity estim ates indicate that significant differences exist betw een literature and study results in 4 out of 5 com parisons. In addition, direct com parison of epoch-level drilling intensity estim ates indicate that significant differences exist betw een literature and study results. Drilling Efficiency Reported drilling efficiency of M. vetusta is -3 6 % (n=11; Kelley and H ansen, 1993) w hereas study results suggest efficiencies of 37% (n=108). Significant differences are not observed betw een th ese two data sources. R eported drilling efficiency of T. alveata is - 8 % (n=26; Kelley and H ansen, 1993) w hereas study results su g g est efficiencies of 40% (n=15). Significant differences (p<0.05) are observed betw een th ese two data sources. Reported drilling efficiency in T. carinata is -89% (n=9; Kelley and H ansen, 1993) w h ereas study results suggest intensities of -5% (n=43). Very highly significant differences ( p « 0 .0 0 1 ) are observed betw een th ese d ata sources. Reported drilling efficiency of T. nasuta is -26% (n=23) w hereas study results suggest intensities of - 8 % (n=26). Very highly significant differences (p<0.001) are observed betw een th e se data sources. In addition to com parisons betw een individual taxa, com parisons can be m ade betw een reported levels of drilling predation for entire units. Kelley and H ansen (1993) reported drilling efficiencies for individual units com parable to this study by combining information on drilling predation into estim ates for all 191 infaunal gastropods. B ecause the Turritella exam ined in this study occupy similar habitats (Allmon, 1988a, 1992a), generalized com parisons can be m ade betw een com bined results from all com parable taxa utilized in this study and estim ates m ade about infaunal gastropods in the study by Keliey and H ansen (1993). For exam ple, Kelley and H ansen (1993) su g g est drilling efficiencies of -3 % (n=49) for the Moodys Branch Formation w hereas study results suggest drilling intensities of -2 2 % (n=187). Very highly significant differences (p<0 .0 0 1 ) are observed betw een drilling efficiency estim ates from th e se data sources. Kelley and H ansen (1993) also sug g est drilling efficiencies of -12% (n=17) for the G osport Sand w hereas study results su g g est drilling efficiencies of -3 6 % (n=149). Very highly significant differences (p<0.001) are observed betw een drilling efficiency estim ates from th ese d ata sources. Kelley and H ansen (1993) suggest drilling efficiencies of 0% (n=14) for the By ram Formation w hereas study results suggest drilling efficiencies of - 6 % (n=95). Highly significant differences (p<0.01) are observed betw een drilling efficiency estim ates from th ese d ata sources. Kelley and H ansen (1993) su g g est drilling efficiencies of -4 % (n=443) for the Cook Mountain interval (com parable to this study’ s results from the Upper Lisbon Stone City Formation) w hereas study results su g g est drilling efficiencies of -1 4 % (n=105). Highly significant differences (p<0 .0 1 ) are observed betw een drilling efficiency estim ates from th ese d ata sources. In sum , taxon-to taxon com parisons of drilling efficiency estim ates indicate that significant differences exist betw een literature and study results in 3 out of 4 com parisons. In addition, com parison of formation-level drilling 192 efficiency estim ates am ong infaunal gastropods indicate that significant differences exist betw een literature and study results in all of the com parable units. Peeling Intensity Reported peeling intensity upon com parable specim ens of T. alveata is -1% (n=15; Allmon et al., 1990) w hereas study results suggest intensities of 60% (n=5). Highly significant differences (p<0.01) betw een these two data sources are observed. Reported peeling intensity upon T. carinata is -0.2% (n=30; Allmon et al., 1990) w hereas study results suggest intensities of - 6 % (n=1694). Very highly significant differences (p<<0.001) are observed betw een th ese data sources. Reported peeling intensity upon T. mississippiensis is -0.3% (n=30) w hereas study results suggest intensities of -2 % (n=1808). Very highly significant differences {p<0 .0 0 1 ) are observed betw een th ese data sources. Reported peeling intensity upon T. perdita is -0.1% (n=30, Allmon et al., 1990) w hereas study results suggest intensities of -11% (n=321). Very highly significant differences (p<0 .0 0 1 ) are observed betw een th ese data sources. Like drilling intensity com parisons, com parisons can be m ade betw een reported levels of peeling predation for entire epochs. For exam ple, Allmon et al. (1990) suggest peeling intensities of -0.3% for the E ocene (n=173 specim ens, n=5 taxa) w hereas study results suggest peeling intensities of - 1 2 % (n=4421 specim ens, n= 1 0 taxa). **Very highly significant differences (p<0 .0 0 1 ) are observed betw een peeling intensity estim ates from these data sources. Allmon et al. (1990) also suggest peeling intensities of -0.1% for the 193 Oligocene (n=45 specim ens, n=2 taxa) w hereas study results suggest peeling intensities of - 2 % {n=1808 specim ens, n=1 taxa). Very highly significant differences (p<0 .0 0 1 ) are observed between peeling intensity estim ates from these data sources. In sum, taxon-to taxon comparisons of peeling intensity estim ates indicate that significant differences exist between literature and study results in all com parable taxa. In addition, direct comparison of epoch-level peeling intensity estim ates indicate that significant differences exist between literature and study results. Summary and Discussion Reported results of a few large-scale predation studies (Dudley and Vermeij, 1978; Allmon et al., 1990; Kelley and Hansen, 1993) have been com pared to study results by utilizing similar taxa, outcrops, and param eters. Although lack of published data (in appendices, etc.) in many large-scale predation studies m akes additional comparisons difficult, comparisons between a few large-scale predation studies and the results obtained in this pilot study suggest that differences do indeed exist between the two. In particular, it appears that there are pervasive differences between published results and study results for taxa which are collected from the sam e outcrop and analyzed for the sam e param eters. Significant differences are noted between these data sources in com parisons m ade between similar taxa, between similar units, and betw een similar epochs. Similarly, significant differences are observed betw een these data sources in comparisons m ade utilizing different param eters, including m easures of drilling intensity, drilling efficiency, peeling 194 intensity, and shell size (although the latter is likely an artifact of sam ple transport). S everal explanations for th e se discrepancies a re possible, including; i) operator error su ch a s variations in the w ay sam ples w ere m easured, analyzed, studied, etc.; ii) differences in sam ple size or ab u n d an ces of constituent taxa; and iii) differences in sam p le com position a s a function of sam ple collection strateg ies (i.e., bulk vs. float sam ples, outcrop vs. m useum collections, multiple vs. single sam ples, lateral & vertical sam pling tran sec ts vs. lateral tran sec ts only). O perator error is unlikely to c a u se such pervasive differences betw een d ata so u rc e s (with th e exception of size discrepancies noted above) b e c a u se sam ple collection, processing, and study techniques a re fairly standardized (se e M ethods section for a m ore detailed sum m ary) and a re not difficult to perform accurately. In addition, results from study localities w ere calculated in exactly the sa m e m anner a s com parable large-scale predation studies. As noted earlier in this study, the potential for bias is great w hen analyzing large-scale p attern s by combining all sp ecim en s in order to obtain estim ates for a given interval, unit, epoch, etc.. This is particularly true b e c a u se abundant tax a tend to hom ogenize patterns of uncom m on taxa or less com m on taxa which do not have extrem e values. It is possible that b e c a u se the com parable large-scale predation studies do not analyze patterns by isolating results for individual taxa (i.e., similar to the two m odes of d ata synthesis utilized in this study— m ixed-species and within-species), tem poral variations a re m ore sensitive to c h a n g e s in relative taxonom ic a b u n d an ces than they a re to levels of predation am ong the studied taxa. With this source of data-synthesis bias in 195 mind, variations in sam ple size or taxonom ic abu n d an ce could c a u se significant differences betw een th e se two d ata sources. B ecause this study collects alm ost an order of m agnitude m ore specim ens from similar outcrops and utilizes a sim ilar num ber of taxa, bias in this study's findings a s a result of th e s e factors are unlikely. If anything, b e c a u se large-scale patterns outlined in published stu d ies u se sm aller (<50 individuals) sam ple sizes, they m ay have larger potential for error and/or bias. S am ple collection strateg ies (sen su latu) are likely responsible for o b serv ed d iscrep an cies betw een large-scale predation studies' results and this study’ s results. As h as been dem onstrated in this study, com parison of m useum - vs. outcrop-based sam ples from the sa m e outcrop yield strikingly different results, depending on the param eter of interest. T h ese discrepancies a p p e a r to be related to the m useum collections and m ay result from lack of bulk sam p le-b ased specim en s in m useum collections, mixture of float and bulk sa m p le s in m useum collections, winnowing/sorting of m useum specim en s a s a result of visitor u sag e, curation, sam ple exchanges, etc., or a com bination of th e s e factors. However, b e c a u se variations in predation p aram eters w ere not pervasive in outcrop-to-m useum com parisons (described earlier in this study), u sa g e of m useum collections m ay not strongly bias results reported in long-term stu d ies of predation. Caution should b e used w hen com paring the two d ata so u rces. If at all possible, th e se results su g g est that one should avoid com bining field- and m useum -based d ata unless one h a s m ad e com parisons (such a s th o se undertaken in this study) to a s s e s s potential b iases in the m useum collection of interest. B ecau se all com parable sam p les from Allmon et al. (1990) and Kelley and H ansen (1993) w ere collected in bulk by th e authors, 196 it is unlikely that m useum -bias is responsible for observed discrepancies betw een d ata sources. With respect to potential biases resulting from collection of float vs. bulk sam ples, Allmon et al. (1990) and Kelley and H ansen (1993) utilize bulk sam ples in their studies. Thus, potential biases resulting from "picking1 1 of selected sam ples from outcrop surfaces is not likely responsible for observed discrepancies betw een d ata sources. Of the remaining four potential biases outlined in above, the only two that rem ain are b iases directly related to the num ber of sam ples collected and the extent of lateral and vertical sampling efforts. B ecause th ese two sampling criteria are closely related to one another, they are considered together. In the sa m e vein, a sse ssm e n t of potential sampling strategy biases is inherently related to the nature of the studied outcrops and th e nature of fossil distribution in th o se outcrops. B ecause outcrops sam pled in th ese studies have been dem onstrated to be characterized by high levels of variability, sam pling strategies should be em ployed which a s s e s s and constrain this variability prior to or coincident with sam ple collection. For exam ple, prior to estim ating intensities of predation for a given outcrop based on one sam ple, it m ay be useful to determ ine if the collected sam ple(s) represents predation intensities of the outcrop in question. A ssessm ent of variability might include analysis of vertical or lateral variability in a given outcrop and as a result, will likely n ecessitate collection of multiple sam ples either within a given horizon or a cro ss a suite of horizons. B ecause this study focused on lateral variability along individual horizons, it is difficult to a s s e s s whether/if vertical variability is responsible for 197 observed discrepancies betw een data sources. Thus, there is a possibility that large-scale predation studies sam pled from different layers than the ones utilized in this study. If different layers represent different lithologic, paleoenvironm ental, or taphonomic regim es, then vertical differences betw een sampling strategies could easily account for observed discrepancies. However, b ecau se many of the sam ples (like those from the Byram Formation) are collected from easily recognizable horizons which are distinct because they are highly fossiliferous (compared to virtually unfossiliferous overlying and underlying strata), it is unlikely that all of the com parable sam ples are collected from vertically different horizons. Thus, it is unlikely that vertical sampling differences account for all of the observed discrepancies betw een data sources. At present, it is not known if variability observed at the studied outcrops results from random processes or whether it exists a s a function of som e type of paleoenvironm ental, taphonom ic, or depositional gradient. B ecause no trends are observed along studied sam ple transects (or within results from these transects) it is thus difficult to a s se ss whether gradient-related variations are responsible for observed discrepancies between data sources. However, b ecau se of the small area of the lateral transects employed in this study, it is difficult to imagine that non-random paleoenvironmental, taphonomic, or other factors play a large role in observed discrepancies. Thus, a s has been dem onstrated by CoBabe and Allmon (1994) and noted by H ansen and Kelley (in press) it appears that many of the fossiliferous horizons in studied outcrops are dom inated by high levels of quasi-random lateral variability, particularly with respect to taxonomic diversity and abundance of constituent taxa, and a s has been dem onstrated in this study, are dominated by high levels of lateral 198 variability am ong size, predation, and taphonom ic characteristics of som e of their more common constituent taxa (i.e., the Turritellidae). With this dom inance of lateral variability in mind, and together with low likelihoods for other m echanism s of observed data source discrepancies (discussed above), I suggest that lateral variability may play a strong role in causing observed discrepancies betw een literature- and outcrop-based data sources. In particular, simplified sampling strategies which do not a s s e s s (e.g., by collecting multiple sam ples and/or sampling along a lateral a s well a s a vertical transect) potential pitfalls of observed lateral variability m ay be responsible for inferred biases present in com parable results from large-scale studies of predation. 199 CONCLUSIONS Lateral variability in characteristics of turritelline gastropod assem blages have been identified in five formations of Middle Eocene to Lower Oligocene strata from the Gulf Coast of the United States. This variability is widespread among the studied param eters in comparisons between taxa in individual sam ples, between sam ples from the sam e outcrop, between outcrops of the sam e formation, and between formations of similar age. Several m ethods of data synthesis and comparison were utilized in this study-all of these methods revealed significant variability at all scales in the studied param eters. Analysis of variability utilizing highly abundant individual taxa proved to be m ost useful in identifying potential sources of lateral variability. For example, among the studied param eters, specim en size characteristics exhibited the most variability (at all scales) in all of the studied taxa. Generalized taphonomic characteristics also exhibited strong variability. Predation characteristics exhibited the lowest variability among the studied taxa. However, som e taxa, such as T. mississippiensis and T. perdita, exhibit extremely high levels of variability in all of the studied param eters and highlight the strong effect individual taxa may have on larger-scale patterns of variability. In addition, similar patterns of variability are noted within and between m useum -based sam ples of the similar taxa from the sam e outcrops. Significant differences are also observed between this study's outcrop-based results and com parable results from m useum -based and literature-based data sources. Although, in general, predation param eters (in museum collections) seem to be minimally affected by potential biases, these results still suggest caution be used when obtaining information from museum collections. Depending on what 200 taxa and param eters are under study, m useum -based sam ples (regardless of whether originally collected in bulk) may not accurately represent the outcrops from w hence they came. Although results indicate that predation param eters are not quite as variable (across studied lateral transects) as other size and taphonomic characteristics, significant differences are pervasive in com parisons of similar literature and study results. This suggests that: i) lateral variability in predation characteristics exists in the studied outcrops; ii) this study’ s sampling strategy utilized enough sam ples to inhibit bias as a result of observed variability; iii) large-scale predation studies may not utilize enough large bulk sam ples to inhibit biases resulting from variability; and/or iv) data synthesis techniques employed in the large-scale predation studies may have artificially biased their results due to taxonomic homogenization or due to skewing by taxa which exhibit high levels of variability in predation param eters (like those noted above). In sum, this pilot study elucidates the high levels of variability present in a num ber of outcrops which are commonly utilized in predation studies and suggest that future sampling strategies need to identify sources of variability prior to identifying any large-scale or temporal patterns utilizing simplified sampling strategies. In order to confidently diagnose large-scale temporal or geographic paleobiologic or paleoecologic patterns, when possible, multiple laterally distinct sam ples should be collected at each vertical horizon under study. The number of sam ples required to avoid encountering a Type I sampling error varies depending on the characteristics of the outcrop or param eter under study. 201 C auses of variability (which differ from sources of variability) are difficult to constrain in this pilot study, but results suggest quasi-random variability is pervasive among the studied outcrops, likely as a result of taphonomic processes, including shell-reworking (e.g., CoBabe and Allmon, 1994). The small size of studied transects and the nature of this study's single-horizon sampling strategies suggests that paleoenvironmental or lithologic variations (especially along a gradient) are not responsible for identified patterns of outcrop-scale lateral variability. Larger-scale cau ses of lateral variability may be operating, and their effects on large-scale predation studies could be better constrained by examining variations along paleoenvironmental or taphonomic gradients (e.g., Hansen and Kelley, in press) in larger, better studied, temporally and geographically constrained units such as the Middle Devonian Hamilton Group of the Appalachian Basin (e.g., Lafferty et al., 1994) or Miocene C hesapeake Group of Maryland. 2 02 REFERENCES A degoke, O .S., and T evesz, 1974, G astropod predation patterns in th e E ocene of Nigeria: Lethaia, v.7, p. 17-24. Alder, H.L., and R oessler, E.B., 1977, Introduction to Probability and Statistics, Sixth Edition: W.H. F reem an and Com pany, S an Francisco, 426 p. Allmon, W.D., 1988a, Ecology of recent turritelline g astro p o d s (Prosobranchia, Turritellidae): current know ledge and paleontological implications: Palaios, V.3, p.259-284. 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Asset Metadata
Creator
Hagadorn, James Whitey
(author)
Core Title
Lateral variability in predation and taphonomic characteristics of turritelline gastropod assemblages from Middle Eocene - Lower Oligocene strata of the Gulf Coastal Plain, United States
School
Graduate School
Degree
Master of Science
Degree Program
Earth Sciences
Degree Conferral Date
1995-05
Publisher
University of Southern California
(original),
University of Southern California. Libraries
(digital)
Tag
geology,OAI-PMH Harvest,paleoecology
Language
English
Contributor
Digitized by ProQuest
(provenance)
Advisor
Bottjer, David J. (
committee chair
), Fischer, Alfred G. (
committee member
), Gorsline, Donn S. (
committee member
)
Permanent Link (DOI)
https://doi.org/10.25549/usctheses-c18-1593
Unique identifier
UC11357548
Identifier
1376458.pdf (filename),usctheses-c18-1593 (legacy record id)
Legacy Identifier
1376458-0.pdf
Dmrecord
1593
Document Type
Thesis
Rights
Hagadorn, James Whitey
Type
texts
Source
University of Southern California
(contributing entity),
University of Southern California Dissertations and Theses
(collection)
Access Conditions
The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...
Repository Name
University of Southern California Digital Library
Repository Location
USC Digital Library, University of Southern California, University Park Campus, Los Angeles, California 90089, USA
Tags
geology
paleoecology