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University of Southern California Dissertations and Theses
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The structure and development of Middle and Late Triassic benthic assemblages
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The structure and development of Middle and Late Triassic benthic assemblages
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THE STRUCTURE AND DEVELOPMENT OF MIDDLE AND LATE TRIASSIC BENTHIC ASSEMBLAGES Copyright 2005 by Nicole Bonuso A Dissertation Presented to the FACULTY OF THE GRADUATE SCHOOL UNIVERSITY OF SOUTHERN CALIFORNIA In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY (GEOLOGICAL SCIENCES) August 2005 Nicole Bonuso Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. UMI Number: 3196779 INFORMATION TO USERS The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. ® UMI UMI Microform 3196779 Copyright 2006 by ProQuest Information and Learning Company. All rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. ProQuest Information and Learning Company 300 North Zeeb Road P.O. Box 1346 Ann Arbor, Ml 48106-1346 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Acknowledgem ents Foremost thanks goes to my advisor, Dr. David J. Bottjer, whose advice and supervision are gratefully acknowledged. Working with him has allowed me to mature significantly as a paleontologist, a scientist, and as an academic. Additionally, I want to thank the members of my committee for their help and time, Dr. Frank Corsetti, Dr. David Caron and Dr. A1 Fischer. Field work could not have been completed without the help of Mike Dinauer at the Berlin-Ichthyosaur State Park, Nevada, Dr. Herbert Summesberger and Dr. Reinhard Golebiowski at the Natural History Museum of Vienna, Austria, Dr. Leopold Krystyn at the University of Vienna, Dr. Franz Stojaspal and Dr. Irene Zorn at the Geological Survey of Austria, Vienna, and Dr. David Haasl at the University of California, Berkeley Museum of Paleontology. I would like to thank Dr. Sandy Carlson, Dr. Christopher McRoberts, and Dr. Michael Sandy, for their discussion on brachiopod and bivalve classification; Dr. Ken Johnson and Dr. Michael Kowaleski for help with statistical questions; and Dr. Jozsef Palfy and Dr. Attila Voros for their kindness in sharing their Hungary data and for their thoughtful discussion. I would also like to thank Dr. David Fastovsky, for introducing me to paleontology, but more importantly, for making himself available by providing generous moral and academic support despite having no formal connection to my research. The trauma of graduate school was reduced greatly by my friendships with Dr. Sara Pruss, Nathanial Lorentz, Catherine Jamet, Kris, Alexander, and Dr. David Bowman, Dena Ackroyd and Dr. Amy Coplan for her friendship and her writing expertise. Last but not least, I want to thank best friend and trusty field assistant, Dr. Matthew E. Kirby. All of this would not have been possible without his encouragement, support, and understanding. Through my Master’s and Doctoral Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iii degree, Matthew has been a welcomed companion on numerous field excursions, has been a sounding board for ideas, thought and concerns about research, teaching, and life. I would like to thank my other family members for their undying support. Although they still think I “dig dirt” for a living they have never stopped giving their much-needed support. Thank you Joe and Jo Bonuso. I cannot forget my two friends, Haden M. Eow and Cooper J. Fox. They continued to provide me with several needed breaks, whether I like it or not, while typing away at the computer. This research was supported by grants from GSA, the American Museum of Natural History, the USC Department of Earth Sciences graduate student research fund, and a USC fellowship. In addition, the Paleobiology Database (PBDB) provided additional support during summers in the form of internships as well as a NSF grant to Dr. David J. Bottjer for the PBDB. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. iv Table of Contents Acknowledgements ii List of Figures vii List of Tables xi Abstract xii Chapter 1: Introduction 1 Hypothesis and Thesis Importance 1 Major Faunal Groups Represented in this Data 2 Brachiopod General Features 2 Brachiopod Evolutionary History 7 Bivalve General Features 13 Bivalve Evolutionary History 18 Gastropod General Features 20 Gastropod Evolutionary History 22 General History of Faunal Replacement 24 Structure of Thesis 29 Chapter 2: General Statistical Methods 30 Data Acquisition 30 Statistical Background 32 Non-parametric Multidimensional Scaling Analysis 34 Detrended Correspondence Analysis 35 Contrast between DCA and NMDS 35 Multi-response Permutation Procedure (MRPP) 36 Searching For Patterns within Ordination Analysis 37 General Understanding 37 Sample Categories 38 Faunal Categories 71 Chapter 3: Early Mesozoic Brachiopod Resurgence: A case study of Middle Triassic and Late Triassic Brachiopod Paleocommunities 73 Abstract 73 Introduction 74 Study Area and Geological Setting 75 Eastern Pacific Realm 78 Germanic Epicontinental Sea Realm 79 Northwestern Tethys Realm 79 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. V Northeastern Tethys Realm 81 Triassic Brachiopod Diversity and Distribution Patterns 82 Methods 83 Sample Collections and Processing 83 Analytical Methods 87 Results 88 Multivariate Taxonomic Analysis 88 Multivariate Ecological Analysis 100 Discussion 105 Conclusion 109 Chapter 4: Late Paleozoic Brachiopod and Bivalve Patterns: A Quantitative Study of Faunal Patterns within the Late Carboniferous and Early Permian 110 Abstract 110 Introduction 111 Study Area and Geological Setting 112 Northwestern Continental Margin Realm 115 Northwestern Midcontinent Realm 115 Southeastern Boreal Realm 118 Methods 118 Sample Collection and Processing 118 Analytical Methods 120 Results 122 Multivariate Taxonomic Analysis 122 Multivariate Ecological Analysis 129 Discussion 143 Conclusion 144 Chapter 5: Paleozoic Brachiopod Communities vs. Modem Brachiopod Communities: A Detailed Paleoecological Analysis Through Time (Pennsylvanian - Late Triassic) 145 Abstract 145 Introduction 146 Methods 147 Data Acquisition 147 Analytical Methods 150 Results 151 Multivariate Taxonomic Analysis 151 Ecological Trends 156 Ordinal Trends 159 Discussion 162 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. C onclusions Chapter 6: The Advantage of Incumbency is Not just For Contemporary Politicians: Brachiopods and Bivalves: A Story of Incumbency, Mass Extinction, and Innovations Abstract Introduction Two Different Groups, Two Different Adaptive Strategies What Are the Faunal Patterns? How Can We Explain These Patterns? How Does This Model Apply to Brachiopod-Bivalve Replacement Patterns? Conclusions Chapter 7: Summary and Future Research Directions Summary Future Research Directions References Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Figures Figure 1: Triassic Fauna 4 Figure 2: Brachiopod Internal Anatomy 5 Figure 3: Brachiopod Life Habits 6 Figure 4: Brachiopod Classification 10 Figure 5: Brachiopod Diversity 12 Figure 6: Brachiopod Diversity Early Mesozoic Resurgence 15 Figure 7: Bivalve Shell Anatomy 16 Figure 8: Bivalve Internal Anatomy 17 Figure 9: Bivalve Life Habits 19 Figure 10: Bivalve Classification 21 Figure 11: Gastropod Anatomy 23 Figure 12: Gastropod Classification 25 Figure 13: Gastropod Evolutionary Patterns 27 Figure 14: Depositional Environment Profile 41 Figure 15: Bird Springs Formation Local Map 42 Figure 16: Bird Springs Formation Stratigraphic Section 44 Figure 17: Pennsylvanian-Permian Midcontinent Stratigraphic Section 45 Figure 18: Wewoka Formation Stratigraphic Section 47 Figure 19: Glass Mountain Stratigraphic Section 49 Figure 20: Locality map of Thailand 50 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 21: Robledo Mountains Locality Map Figure 22: Environmental Reconstruction (Yancey and Stevens, 1981) Figure 23: Esino Limestone Stratigraphic Section Figure 24: Anisian Terebratula Beds Stratigraphic Section Figure 25: Zaimostie Formation Stratigraphic Section Figure 26: Felsoors limestone Formation Stratigraphic Section Figure 27: Leidapo Member Environmental Interpretation Figure 28: Cassian Formation Stratigraphic Section Figure 29: Kossen Formation Stratigraphic Formation Figure 30: Kossen Formation Environmental Reconstruction Figure 31: Luning Formation Stratigraphic Section Figure 32: Gabbs Formation Stratigraphic Section Figure 33: Middle and Late Triassic Paleogeography Figure 34: Middle and Late Triassic Geochronology Figure 35: Middle Triassic Genera and Order Ordinations Figure 36: Middle Triassic Genera Ecological Category Plots Figure 37: Middle Triassic Samples and Specimen Ordination Figure 38: Late Triassic Genera and Order Ordinations Figure 39: Late Triassic Genera Ecological Category Plots Figure 40: Late Triassic Samples and Specimen Ordinations Figure 41: Middle Triassic Ecological Analysis Ordinations Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IX Figure 42: Late Triassic Ecological Analysis Ordinations 102 Figure 43: Middle Triassic Ecology vs. Samples Ordinations 103 Figure 44: Late Triassic Ecology vs. Samples Ordinations 104 Figure 45: Late Carboniferous and Early Permian Paleogeography 113 Figure 46: Late Carboniferous and Early Permian Geochronology 114 Figure 47: Late Carboniferous Genera and Order Ordinations 123 Figure 48: Late Carboniferous Genera Ecological Category Plots 124 Figure 49: Late Carboniferous Samples and Specimen Ordinations 126 Figure 50: Early Permian Genera and Order Ordinations 127 Figure 51: Early Permian Genera Ecological Category Plots 128 Figure 52: Early Permian Samples and Specimen Ordinations 130 Figure 53: Late Carboniferous Ecological Analysis Ordinations 134 Figure 54: Early Permian Ecological Analysis Ordinations 135 Figure 55: Late Carboniferous Ecology vs. Samples Ordinations 136 Figure 56: Early Permian Ecology vs. Samples Ordinations 137 Figure 57: Paleozoic and Early Mesozoic Geochronology 148 Figure 58: Brachiopod and Bivalve Diversity Model 149 Figure 59: Paleozoic and Early Mesozoic NMDS Ordination 152 Figure 60: Paleozoic and Early Mesozoic Life Habits 157 Figure 61: Paleozoic and Early Mesozoic Substrate Preferences 158 Figure 62: Paleozoic and Early Mesozoic Bivalve Ordinal Patterns 160 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 63: Paleozoic and Early Mesozoic Brachiopod Ordinal Patterns 161 Figure 64: Paleozoic Detailed Ecologies 173 Figure 65: Early Mesozoic Detailed Ecologies 175 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. List of Tables Table 1: Middle Triassic Sample Descriptions Table 2: Late Triassic Sample Descriptions Table 3: Triassic Generic Codes Table 4: Percentage of Epifaunal vs. Infaunal per Sample Table 5: Middle Triassic Taxonomic MRPP Results Table 6: Late Triassic Taxonomic MRPP Results Table 7: Middle and Late Triassic Ecological MRPP Results Table 8: Late Carboniferous Sample Descriptions Table 9: Early Permian Sample Descriptions Table 10: Late Carboniferous Taxonomic MRPP Results Table 11: Early Permian Taxonomic MRPP Results Table 12A: Late Carboniferous Brachipod Generic Codes Table 12B: Late Carboniferous Mollusc Generic Codes Table 13A: Early Permian Brachipod Generic Codes Table 13B: Early Permian Mollusc Generic Codes Table 14: Late Carboniferous/Early Permian Ecological MRPP Results Table 15: Paleozoic and Early Mesozoic MRPP Results Table 16: Paleozoic and Early Mesozoic Ratios Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xii Abstract This study documents brachiopod and bivalve relative abundance patterns from the Middle and Late Triassic. Brachiopod- and bivalve-dominated fossil assemblages from before and after the end-Permian mass extinction were analyzed to gain perspective on the brachiopod radiation within the early Mesozoic and to more completely understand the causal mechanisms behind the switch between Paleozoic brachiopod-dominated faunas and Modem bivalve-dominated faunas. Using data from bulk samples, this study examines quantitative patterns recorded by marine benthos. In total 387,992 specimens were pooled from primary and summary literature resources, including 21,671 Middle and Late Triassic specimens from Italy, Poland, Slovakia, Hungary, China, Austria, and Nevada. In addition, a total of 336,321 Late Carboniferous and Early Permian specimens were analyzed from Nevada, Kansas, Oklahoma, Texas, Utah, New Mexico, Venezuela, Thailand, and Australia. For each time interval (i.e., late Paleozoic and early Mesozoic), multivariate statistics determined whether paleogeography, depositional environment, age, substrate preference, or taxonomic membership influenced faunal patterns and if so, to what extent. Both time intervals reveal that ecological preferences largely control faunal patterns. That is, the abundance of sessile benthos (epifaunal brachiopods and bivalves) versus mobile benthos (infaunal bivalves and grazing gastropods) controlled faunal distributions. Comparison of late Paleozoic and early Mesozoic faunal patterns indicates that taxonomic structure differed between time intervals. The late Paleozoic faunas consisted of numerous brachiopod orders varying in their attachment modes, compared to the one order of shallow burrowing deposit-feeder bivalves. In contrast, the Middle Triassic records a decrease in brachiopod diversity compared to bivalves and the fauna consisted primarily of epifaunal brachiopods and bivalves. As the Late Triassic approached, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. xiii infaunal suspension feeding bivalves slowly replaced epifaunal brachiopods and bivalves. Faunal patterns reveal that Middle Triassic faunas represents a stress- tolerant, sessile fauna suggesting that environmental disruption leading to the end- Permian mass extinction affected oceanic condition such that stress-tolerant faunas continued into the Middle Triassic. Slowly, from the Middle to Late Triassic, high energy, mobile fauna replaced this stress-tolerant fauna. As a result, the brachiopod to bivalve switch was due to a combination of brachiopod incumbency, mass extinction, and key bivalve adaptations. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 Chapter 1: Introduction Hypothesis and Thesis Importance This thesis tests the hypothesis that ecological interactions strongly influenced brachiopod and bivalve faunal replacement patterns by completing rigorous paleoecological analysis of Middle and Late Triassic faunas during a brachiopod “revival” period. The causal mechanism for the switch between brachiopod-dominated faunas to bivalve-dominated faunas has been a long sought after question. It is now generally accepted that the incumbent brachiopods were severely affected by the end-Permian mass extinction. As a consequence, they were replaced in benthic marine environments by bivalves (Donovan and Gale, 1990; Gould and Calloway, 1980; Miller and Sepkoski, 1988; Sepkoski, 1996). These early replacement studies, along with others, based their conclusions on taxonomic data and/or taxonomic diversity patterns. It remains unclear, however, how large- scale ecological processes affected this replacement. Perhaps the process of biotic replacement is more complex then just a simple switch of dominance. Most likely, ecological interactions and environmental factors strongly influenced brachiopod and bivalve macroevolutionary patterns, yet little paleoecological analyses have been accomplished. Thus, it is likely that brachiopods and bivalves share a more complex history during this early Mesozoic transitional period than previously observed. To help understand this pattern further, a large-scale ecological study, including both brachiopod and bivalve community data, must be analyzed rigorously. Many previous studies have analyzed brachiopod (Michalik, 1987) and bivalve communities (Komatsu et al., 2004; McRoberts, 2001) specifically, but the two groups have yet to be analyzed together in a consistent, statistical manner. The range of controlling factors of faunal replacement is broad; therefore, future macroevolutionary studies should include a full range of biological, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 2 ecological, and environmental components. This study uniquely integrates all of the latter components needed to answer questions concerning replacement processes making this study important on many interesting levels: 1) it provides insight into the “classic” faunal transition from brachiopod dominance to bivalve dominated communities; 2) it puts forth the first rigorous paleoecological analysis of Middle to Late Triassic benthic marine communities; and 3) it proposes general mechanisms controlling faunal replacement patterns. Major Faunal Groups Represented in this Data Three taxonomic groups dominate this dataset: brachiopods, bivalves, and to a lesser extent, gastropods. General anatomical information along with the latest classification schemes, ecological preference and evolutionary histories of each group is reviewed below. Figure 1 displays a representative group of major Middle and Late Triassic taxa. Brachiopod General Features Generally brachiopods are not familiar animals. These solitary organisms secrete a shell consisting of two valves that enclose the animal (Figure 2A). Since brachiopods posses a two-valved shell, they are often superficially mistaken as a bivalved mollusc, especially clams. However, there is little similarity between the two groups beyond these two valves. Moreover, their phylogenic histories are not related leading to major differences between the anatomies of the two groups. All living brachiopods are marine and there is no fossil evidence suggesting that any brachiopod ever successfully invaded fresh water environments. However, various individuals live in a range of environments from the shoreline to the deep ocean floor between the polar regions and the tropics. All fossil evidence suggests that their Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 3 habits have been at least as varied, if not more so, in the past (Grant, 1981; Peck, 2001a; Rudwick, 1970). The calcitic brachiopod shell is its most conspicuous part. As mentioned above, the shell consists of two parts or valves, which enclose almost all of the internal organs. Unlike bivalved molluscs, brachiopod shells almost always show bilateral symmetry through the two valves and not between the valves as in clams (Figure 2B). As seen in Figure 2A, the two oval calcareous valves differ in size. The valves have been referred to as dorsal and ventral however, when brachiopods are fixed by their pedicle, they have both valves vertical making the distinction of dorsal and ventral difficult. To avoid any confusion, the valves are distinguished as brachial and pedicle because these terms refer to structures contained within the valves rather than orientation of the organism. The simplest way to differentiate valves is by finding the valve that possesses the pedicle foramen, the opening from which the pedicle emerges; this is the pedicle valve. If a pedicle foramen cannot be found, the pedicle valve is usually the larger of the two valves. The internal anatomy of brachiopods is displayed in Figure 2C. Beginning with the mantle the only organ contained within this region is the lophophore, the main organ responsible for feeding and respiring. Within most brachiopods the lophophore has a hydrostatically supported fluid-filled canal (termed the brachial canal) at its axis (Williams, 1965). A long loop-shaped calcareous band, the brachidium, which is attached to the inside of the brachial valve, supports the brachial canal. The brachidium can get extremely complex and spiral in some brachiopod orders. The body cavity is separated from the mantle cavity by the body wall. The body cavity is filled with muscles for opening and closing the shells as well as organs to aid in digestive processes. The pedicle and related structures are also housed inside the body cavity. The pedicle, used to anchor the organism, is a Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Figure 1: Typical Middle and Late Triassic fauna. A-I represents some of the dominant Middle Triassic genera; J-S represents some of the dominant Late Triassic genera. (A) Brachiopod, Coenthyris sp.; (B) Brachiopod, Mentzelia sp.; (C) Gastropod, Eucyclocala sp.; (D) Gastropod, Worthenia sp.; (E) Brachiopod, Tetractinella sp.; (F) Brachiopod, Deurtella sp.; (G) Brachiopod, Dinarispira sp.; (H) Bivalve, Daonella sp.; (I) Bivalve, Cassianella sp.; (also present in Late Triassic dataset); (J) Brachiopod, Zeilleria sp.; (K) Brachiopod, Fissirhynchia sp.; (L) Bivalve, Lopha sp.; (M) Bivalve, Septocardia sp.; (N) Brachiopod, Zugmayerella sp.; (O) Brachiopod, Rhaetina sp.; (P) Bivalve, Nuculana sp.; (Q) Gastropod, Rhapistomella sp.; (R) Brachiopod, Oxycopella sp.; (S) Bivalve, Gervillia sp. Genera are drawn approximately to scale. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 5 Plane of symmetry Pedicle valve Pedicle valve Brachial valve Pedicle Valve Adductor Muscle Mantle Cavity Diductor Muscle Lophophore Pedicle opening Brachidium Pedicle Brachial valve Body wall Figure 2: Brachiopod anatomy. (A) lateral view of brachiopod shown in life position (after Davis, 1851 and Clarkson, 1993); (B) median plane showing brachiopod bilateral symmetry (C) stylized median section showing general internal organs (after BIODIDAC project - http://biodidac.bio.uottawa.ca) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 cylindrical stalk that is fixed to the pedicle valve, which aids in orienting the shell with changing wave direction. All living brachiopods are sessile, benthic organisms that primarily fix to some object on the seafloor such as rocks, other shells, or a reef by their soft-tissue pedicle. The attachment is permanent with an exception of a short larval interval where they can swim or drift with the current, allowing them to move to another area. A few individuals can attach directly to the soft bottom and others remain unattached and simply recline or sit on the soft-bottom ocean floor. One group of brachiopods lives infaunally, however, the majority of the brachiopods within this research do not inhabit the substrate. Fossil brachiopods display a wide variety of attachment modes; the most common mode is attachment by their pedicle to a hard substrate (Figure 3). Brachiopod pedicles actually have remarkable attachment strengths allowing them to live abundantly in subtidal currents (Rowell and Grant, 1987). The pedicle is capable of considerable modification. The most surprising life habit has been discovered in terebratulides from the southern coast of Australia. These brachiopods posses a pedicle and muscle system designed to allow the shell to move up and down in the sediment and to push it around on the seafloor (Clarkson, 1986). Therefore, the presence of a pedicle opening in fossil brachiopods may not be an indicator that the organism was attached to the sea floor. Cementation is another form of life habit but this lifestyle is fairly uncommon and is confined to one small group (Rowell and Grant, 1987). Brachiopods range in environment from shallow-water shelf settings to deep-water environments associated with seamounts (Sandy, 1995). As a general statement it can be said that this group is gregarious and cosmopolitan when the environment is advantageous for them. Interestingly, brachiopod shell form Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 seems to be generally correlated with environment. It has been recognized that Paleozoic orthides with coarse ribs preferred arenaceous environments, and equally this trend seems prominent in Mesozoic brachiopods. Evidence indicates that similar anatomical features occur in unrelated stocks in similar environments. For example, any assemblage from very shallow waters generally includes coarse ribbed rhynchonellides with large pedicle openings supporting corpulent pedicles as well as terebratulides with a sharp commissure. Reef environments tend to include large asymmetric rhynchonellides and terebratulides with elongated umbos. In addition, there are some peculiar small, thinly shelled rhynchonellid brachiopods that were evidently epiplanktonic as well as some punctate terebratulides that were confined to calm, deep waters. In sum, many researchers have concluded that environment and substrate characteristics largely dictate brachiopod distributions (Ager, 1965; Fiirsich and Hurst, 1974; Sandy, 1995; Tchoumatchenco, 1972). Brachiopod Evolutionary History Brachiopods are one of the only seven phyla that span the entire Phanerozoic; their fossil record begins in the earliest Cambrian and distant relatives (Figure 3) of these ancient individuals occur in our present day deep oceans and seas. Recently brachiopod classification revision has split this phylum into three new subphyla and over twenty orders (Carlson and Leighton, 2001) (Figure 4). The Rhynchonelliformea subphylum comprises nearly 95% of brachiopod species (Williams et al., 2001). As a result, the majority of brachiopods within this study are classified as rhynchonelliform brachiopods. These rhynchonelliform brachiopods became the dominant shelly animal on the seafloor of tropical, temperate, and polar regions of the Paleozoic (Cooper, 2001). These dominant brachiopods constitute a portion of what Jack Sepkoski termed the “Paleozoic fauna”. Factor analysis of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 8 Pedicle valve Brachial valve interarea propelled water Direction of movement Sensory spines ? Figure 3: Ancient brachiopods displayed a wide variety of attachment modes. (A) most attached by their pedicle to a hard substrate or to nearby rock or shells; (B) others possessed broad interareas upon which they lay on the sea floor; (C) some permantently cemented to the substrate by their broad base; (D) cup shaped productids tended to sit in the mud, with their spines holding them into place; (E) the concavo-convex strophomenides may have propelled themselves along the bottom by shooting water out of their mantle; (F) the concano-convex strophomenidines rested with their concave valve upward, using their curvature to keep the shell out of the mud (after Neid and Tucker, 1985). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 9 Phanerozoic marine diversity indicates that the diversity curve can be broken down into three “evolutionary faunas”: the “Cambrian fauna”, the “Paleozoic fauna” and the “Modern fauna” (Sepkoski, 1978,1979,1981,1984). The “Paleozoic fauna” extended from the Ordovician through the Permian and rhynchonelliform brachiopods comprise a large portion of the total fauna. This faunal dominance was completely rearranged after the end-Permian mass extinction and during the Triassic the “Modem fauna” arose which was dominated in part by bivalves and gastropods. Linguliform brachiopods initiated the first brachiopod radiation in the Early Cambrian and dominated the Cambrian-Middle Ordovician shelly fauna known as the Cambrian fauna (Bassett et al., 1999). The oldest rhynchonelliforms appeared in the middle Early Cambrian, but began their radiation later, in the Middle and Late Cambrian (Cooper, 2001). By the Late Ordovician, most of the brachiopods that came to dominate the Middle Paleozoic had become successfully established and diversified (Figure 5). By this time, orders such as the Orthida, Strophomenida, Pentamerida, Rhynchonellida, and Atrypida, began to replace the Cambrian linguliform brachiopods (Cooper, 2001). These orders are known to from a significant part of the marine benthic fauna known as the “Paleozoic fauna” (Sepkoski, 1981). These brachiopods dominate many substrates, especially equatorial settings of the large, flooded cratons that produced shallow, eperic seas. Orthides and strophomenides dominated much of the Early and Middle Ordovician; some of the flat-shelled, strophomenides even reached widths of 5-6 cm, implying that their convex life style was particularly successful (Cooper, 2001; Leighton and Savarese, 1996). By the Early Silurian, brachiopod communities comprised the dominant groups of the Middle Paleozoic. The dominant families of Orthida, Strophomenida, Rhynchonellida, Pentamerida, Atrypida, and Spiriferida evolved at this time and later, became the dominant orders of the Devonian (Cooper, 2001; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 10 Paleozoic Cenoz. Mesozoic Camb 1 Ord I Sil Dev I Carb [Perm Tr 1 Jur I Cret Lingulida Siphonotretida . Acrotretida ^SSBH BKISerinida UNGULIFORMEA Crannda Craniopsida CRANIIFORMEA Tnmerellida Chied Dictyonellida RH Y NCHONELLIFORMEA Orthotetida u Obolellida Billingsellida Strophomenida Productida Protorthida Pentamerida Orthida Atrypida Spinfenmda Spiriferida Thecideida Athyndida Terebratuiida Rhychonellida Figure 4: Stratigraphic range chart and tentative hypothesis of relationships among brachiopod orders, (after, Williams et al., 1996 and Carlson and Leighton, 2001). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 Leighton and Savarese, 1996). In carbonate shelf and ramp settings, brachiopod assemblages ranged from onshore to offshore, forming vast pavements, each with their own distinct niche. Once again brachiopods grew to substantial sizes, reaching 10-15 cm in width or length, which allowed them to occupy much of the seafloor (Cooper, 2001). During the Silurian and Devonian, rhynchonelliform brachiopods steadily became more abundant and probably reached their highest peak in diversity in the Devonian (McGhee, 1996; Rudwick, 1970) (Figure 5). Toward the end of the Devonian this steady expansion and radiation of the phylum was brought to an end by the Late Devonian mass extinction (McGhee, 1988, 1996; Rudwick, 1970) (Figure 5). During this time most major orders exhibited limited diversity patterns while the dominant pentamerides and atrypides became extinct along with many of the primitive terebratulides (Cooper, 2001) (Figure 4). The rhynchonellides, terebratulides, and spiriferides however, seem to have been little affected, and subsequently expanded in the early Carboniferous period through the Late Permian (Cooper, 2001; Rudwick, 1970). Similarly the strophomenides capable of cementation expanded in place of the earlier free-lying ancestors. Thus, a new fauna emerged in the early Carboniferous characterized by strongly concavo-convex, spinose productids that typically used their spines as anchorage in soft substrates (Grant, 1981) (Figure 3D). Spinose chonetids, with flat shells and peculiar long, often asymmetrically arranged spines, diversified in the Late Paleozoic. Likewise, bilobed to heart shaped rhynchonellid groups arose in the Late Paleozoic, marking the final phase of rhynchonellid diversification into new morphologies (Savage, 1996). The close of the Permian recorded the most catastrophic Phanerozoic mass extinction for the phylum, wiping out all the dictyonellides, orthotetides, orthides, and spiriferides, a number of which showed decline before the boundary (Figure 4). This mass extinction largely left the subphyla Linguliformea, the epibenthic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Diversity 12 50 40 30 20 10 500 400 300 200 100 Camb. Ord. I Sil. Dev. I Carb. I Perm. I Tr. Jur. I Cret. Tertiary Geological Time Figure 5: General species diversity curve for brachiopods through the Phanerozoic. Note the high levels of diversity reached within the Paleozoic. Data compiled from the 1969 Treatise of Invertebrate Paleontology (after Rudwick, 1970). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 13 Craniiformea, and conservative pedunculate Rhynchonellida and Terebratulida stocks unscathed (Cooper, 2001). After the Permian-Triassic mass extinction, brachiopod genera never reached their former Paleozoic diversity high. Brachiopods did resurge to reach a generic diversity of 61 or higher in the Late Triassic, Middle Jurassic, Miocene and Holocene (Figure 6). The only numerically significant orders during the Triassic were Spiriferinida, Rhynchonellida, and Terebratulida. The Triassic actually marks the start of a post-Paleozoic radiation of Terebratulida. The Terebratulida appear to have been taking advantage of available niche space at the extinction. Once in these vacant niches, the Terebratulida experienced a series of radiations and extinctions associated with Anisian, Ladinian, Camian, Norian, and Rhaetian stages (Sandy, 1998). By the Late Triassic Spiriferinida were diverse at the genus-level and well represented in marine sequences although they did not survive beyond the Early Jurassic leaving only rhynchonellides and terebratulides as survivors until the present day (Sandy, 1998). Bivalve General Features As mentioned, bivalves look superficially like brachiopods; however, bivalve shells are symmetrical between the two valves, so that the right valve is usually a mirror image of the left valve (Figure 7). The valves are joined by a hinge on the dorsal side of the animal along a line parallel to the length of the body. Unlike brachiopods, the internal shell cavity of a bivalve does not contain a lophophore. Instead, the mantle cavity consists of a small headless body and visceral mass (Figure 8). The gills occupy the largest part of the shell volume and serve as the main filter-feeding device and respiratory organ. Along with the gills, the body cavity contains a simple digestive tract, including a stomach and intestines as well as a mouth and anus. Bivalves also possess a long flexible foot, which Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 14 protrudes from the front of the shell and is used to dig down into sediment. In most modem burrowing bivalves, the posterior portion of the body contains a pair of long siphons that extrude from the mantle, reaching to the water above (Figure 9). Water is drawn down through the inhalant siphon to the animal through ciliary pumping action of the gills. From there, the gills process the food particles until it reaches the mouth. Wastewater and excrement is then cleared from the animal through the exhalant siphon. Other important difference exist between brachiopods and bivalves, one being musculature differences. While brachiopods possess a pair of opposing muscles (i.e., adductor and diductor), bivalves only possess adductor muscles, which are capable of tremendous strengths in holding the valves shut. All bivalves are aquatic, with the majority of types living in shallow marine waters. There is however a single group of freshwater forms most of which are sluggish and sit on the bottom, or burrow into the sand and mud (Stanley, 1970). Like brachiopods, bivalves are a very diverse group that have adapted to a large number of lifestyles. Modem bivalves can be grouped into a number of ecological categories: infaunal shallow burrowing; infaunal deep burrowing; epifaunal, attached by byssus threads to the substratum; epifaunal, cemented to the rock; free- lying; swimming; and boring and cavity-dwelling (Figure 9) (Newton and Laporte, 1989; Stanley, 1968, 1970; Valentine, 1973). The shape and general morphology of bivalve shells directly reflects their mode of life. From an understanding of the ways in which modem bivalves are adapted to particular modes of life one can make reasonable inferences on how extinct bivalves lived (Stanley, 1970). For example, most burrowing bivalves have equivalved shells with two isomyarian (i.e., equally sized) adductor muscles (Stanley, 1970). In addition, generally, circular shells tend to rock back and forth at a greater angle than elongate shells, which tend to penetrate the substrate vertically. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Genera 15 200 180 160 140 120 100 80 60 40 20 0 Carb. Triassic Jurassic Cenozoic Perm. Cretaceous Time Figure 6: Brachiopod diversity from the Carboniferous through the Holocene Note brachiopod diversity increase during the M iddle and Late Triassic indicated by the circle (data from Gould and Calloway, 1980). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 16 siphona Lateral view of left valves Posterior view Anterior view Figure 7: Bivalve morphological features indicating the position of foot and siphon within the two shells. Anterior and posterior views show bilateral symetry, which runs along a plane between the two shells (after Moore et al., 1969). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 17 Stomach Anterior adductor muscle Mouth Foot Anus Intestine Posterior adductor muscle Gill Ligament Shell Gill Mantle cavitiy Gut Mantle Foot Figure 8: Bivalve internal morphology. (A) right lateral view of animal showing internal organs (after BIODIDAC http://biodidac.bio.uottawa.ca/); (B) vertical cross-section of the animal (after Clarkson, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 18 Bivalve Evolutionary History Bivalves, a class belonging to one of the seven phyla extending through the Phanerozoic, have had numerous classification schemes proposed. The most popular and widely accepted system is that of Newell in the Treatise on Invertebrate Paleontology (Moore, 1969). The classification proposed by the Treatise gives the following classes and orders found in Figure 10. The earliest evidence of the class Bivalvia begins during the Tommotian age, nearly 530 million years ago, within the Early Cambrian (Schneider, 2001). These early forms seem to have disappeared by the end of the Middle Cambrian, leaving no record of bivalves through the Late Cambrian until the early Ordovician, at which time the Palaeotaxodonts appeared (Pojeta et al., 1987). The two other great clades, the Autobranchia or Autolamellibranchiata, do not appear until the middle Ordovician, and are clearly derived from the Palaeotaxodonta (Giribet and Wheeler, 2002). Although the major taxa of bivalves were established in the early Ordovician, they remained limited in their diversity and abundance through much of the Paleozoic. During the early Paleozoic, epifaunal and primitive infaunal siphonate suspension feeding dominated the life mode of bivalves. Infaunal siphon feeders appeared in the middle and late Paleozoic, but they gained prominence after the Permian-Triassic mass extinctions (Stanley, 1968). Since the Triassic, the infaunal and epifaunal forms increased in diversity until the Cretaceous-Tertiary boundary, when the epifaunal suspension feeders were decimated (McRoberts, 2001). During the Cenozoic, the infaunal siphonate clams continued to diversify. Many researchers conclude that this great expansion of infaunal siphonate bivalves between the Jurassic and the present, has been largely due to their ability to exploit previously uninhabited niches (Bottjer, 1985; Crame, 2002; Stanley, 1968). The deposit feeders Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 19 Figure 9: Bivalve life positions with arrow indicating water currents. (A-C) Epifaunal suspension feeders; (A) Oyster; (B) Pterioid; (C) Mytiloid; (D-E) Infaunal siphon feeders; (F) Nuculoid, non- siphonate, deposit feeder; (G-H) infaunal non-siphonate suspension feeders; (I) mucus tube feeder; (J- K) infaunal siphonate bivalves (after Stanley, 1968). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 20 and the mucus-tube builders evolved early in the Paleozoic and remained relatively unaffected by the mass extinctions and diversification of the other mollusc classes (Stanley, 1968). Gastropod General Features Gastropoda, snails and slugs, represent the largest and most diverse mollusc class. Most gastropods have a single, generally spirally coiled shell into which the body can be withdrawn (Figure 11). Gastropods have four main parts: a visceral mass, mantle, head and a muscular foot that is used for “creeping” locomotion in most species (Prothero, 2004). The muscular foot runs the entire length of the ventral surface of the body. The entire body may be withdrawn into the last whorl of the shell and in many marine snails the opening may be closed with a plug called an operculum, which is attached to the posterior surface of the body. This plug blocks the opening and protects the animal from predators or other dangers. The head, which contains tentacles, a mouth, and eyes, is highly developed and bilaterally symmetrical. The mouth contains a radula that helps process food, but has adapted to serve many different purposes. The majority of the gastropod’s digestive, respiratory, and reproductive systems are coiled in a spiral, which is enclosed in, and is protected by, the shell. The lining of the mantle cavity is ciliated to facilitate water flow over the gills. From the radula, these ciliary currents transport food through the digestive tract to the stomach and finally through the excretory system. Also found on the upper surface of the mantle cavity is the osphradium, an organ capable of sensing chemical changes in the environment. Other components of the nervous system include cerebral ganglia, eyes, and olfactory tissues, which are most often located within the tentacles. The most distinct feature of the gastropod anatomy is torsion. Torsion is a process that twists the body around 180° such that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 21 NEWELL 1965,1969 PALAEO- TAXODONTA Nuculoida CRYPTO- DONTA Solemyoida Praecardioida < £ Arcoida £ o S o 2 w H 0, Pteroida Mytiloida PALAEO- HETERODONTA Modiomorphoida (Actinodontioda) Unionoida Trigonioida e S Z ft Hippuritoida a o at W H Veneroida Myoida 2 a Pholadomyoida r, 2 < a Poromyoida Figure 10: Bivalve classification according the Treastise of Invertebrate Paleontology (1965, 1969). Subclasses are listed on the left and orders are listed to the right. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 22 the anus moves into a position directly over the head and is thought to be helpful in many ways. First, it moves the mantle cavity and osphradium to the front of the animal so that the water can be sensed earlier than it could be with the osphradium located at the posterior end of the organism. Second, the sediment stirred up by the snail’s movement is less likely to clog the gills if they are located at the front of the organism. Gastropod systematics has undergone major revision in the last few decades. As a result, workers in this field no longer accept the older classification system that divides Gastropoda into three subclasses (i.e., Prosobranchia, Opisthobranchia, and Pulmonata) (Bieler, 1992; Ponder and Lindberg, 1997; Vaught, 1989; Wagner, 2001). A cladistic approach has been adopted based on recent research but older terms are still found in older textbooks and are used as generic categories. Tentative alternatives to the traditional classification include two subclasses: Eogastropoda and Orthogastropoda (Ponder and Lindberg, 1997). The data used for this analysis contains primitive gastropods from both subclasses and within orders that have yet to be classified. Orders such as Bellerophontida, Euomphalida, Murchisoniida, and Neotaeniglossa are present within this dataset (Figure 12). In general, all of the orders represented are herbivorous that graze along the ocean bottom. Gastropod Evolutionary History Because most gastropod evolutionary histories are written using an older classification scheme, the older subclass divisions, Prosobranchia, Archaeogastopoda, and Neogastropoda, will be used in this next section. Figure 12 is structured to aid in the discussion of new and old classification systems. There are three basic trends in gastropod evolution: conversion from herbivorous to a carnivorous diet, a shift from an oceanic existence to terrestrial and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 23 Inhalent siphon Mantle fold Penis Shell Operculum Eye Tentacle Foot Mouth Figure 11: Morphology of a orthostrophic gastropod. That is, a gastropod that has the whorls displaced to the right side, which is carried diagonally over the back with the apex pointing backward and to the right of the animal. A variety of orthostrophic gastropods dominated the Paleozoic but declined during the Mesozoic (after Clarkson, 1993 and Prothero, 2004). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 24 fresh-water habits, and the loss of the shell (Prothero, 2004). The most primitive gastropods are the prosobranchs, which contain the earliest fossil gastropod yet found. The earliest genera are Early Cambrian and by the Late Cambrian, Archaeogastropods were already radiating rapidly, a trend that has generally continued right up until recent times (Levin, 1999) (Figure 13). In the early prosobranchs of the Cambrian, there is already evidence of a shift to a carnivorous diet from the ancestral habit of grazing on algae and fungi. Also, torsion began to develop, a condition associated with more efficient respiration. The opisthobranchs, which arose in the Mississippian (i.e., Late Carboniferous) most likely have ancestors in the primitive prosobranchs and have shown extensive reduction of the visceral hump and shell. Overall, gastropods have been remarkably successful, radiating extensively and often withstanding mass extinction events that decimated other taxa (Levin, 1999). General History of Faunal Replacement Studies What is the mechanism that causes one species to replace another? Inference of competitive extinction, with its classic processes of genetic drift, adaptation, competition, and survival of the fittest, traditionally answers this question. Essentially, the new outcompetes the old due to a progressive evolutionary adaptation. Darwin’s metaphor of the wedge is an excellent example of this doctrine. Nature is compared to a surface covered with numerous sharp wedges that are driven by successive improvements; the progressive species eventually expels an inferior species (Stauffer, 1975). This model of competitive exclusion along with the idea of pure chance, in which each taxon radiates unopposed, provides the foundation for faunal replacement; however, with further research it is clear that faunal replacement incorporates more variables then just competition and chance (Benton, 1987, 1996; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 25 Incertae Sedis (primitive forms - Prosobranchia / Archaeogastropoda in part) Order "Tropidodiscida" ("Bellerophontina" in part) Order Bellerophontida ("Bellerophontina" in part) Order Cocculinida (polyphyletic?, may be either Eogastropod or Orthogastropod) Subclass Eogastropoda (primitive forms - Prosobranchia / Archaeogastropoda in part) Order Euomphalida Order "Platycerida" (normally a superfamily, see note) Order Patel logastropoda (Docoglossa) Subclass Orthogastropoda (all other gastropods) Infraclass unnamed (Prosobranchia in part)) Superorder unnamed (Archaeogastropoda in part) Order Murchisoniida Order Neritopsina Order Neomphalida Order Veti gastropoda Superorder Caenogastropoda Order Architaenoglossa Order Neotaenioglossa Order Neogastropoda Infraclass Allogastropoda Order Heterostrophia Infraclass Opisthobranchia Order Architectibranchia Order Cephalaspidea Order Anaspidea Order Thecosomata Order Gymnosomata Order Sacoglossa Order Umbraculomorpha Infraclass Pulmonata Order Systellommatophora Order Basommatophora Order Stylommatophora Figure 12: Gastropod classification scheme suggested by Ponder (1997). Older subclass names such as Prosobranchia and Archaeogastropoda are found in parentheses to aid with classification transitions. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 26 Benton and Simms, 1995). Further investigation presents five models of expected clade radiation patterns due to biotic replacement (Benton and Simms, 1995). Type 1: Competitive replacement depicts a well-adapted clade that allows it to compete successfully with, and replace, members of another clade. The surviving clade therefore demonstrates competitive superiority. Type 2: Post-extinction competitive replacement describes a situation during an extinction event. In this scenario, one clade competes successively in the disturbed post-extinction ecosystem with the survivors of another clade. Type 3: Extinction resistance illustrates a clade that resists extinction during a time when other taxa are dying out. However, the surviving organisms do not interact in any way. Type 4: Noncompetitive adaptive radiation depicts an extinction event during which many organisms die out, and by chance, only a few organisms survive; these survivors’ posses an adaptation that ensures a successful radiation. Type 5: Noncompetitive radiation also occurs during an extinction event in which many organisms die out however, in this model, the survivors do not possess a particular adaptation and simply radiate by chance. In recent years, a number of major faunal replacements previously regarded as competitive have been reinterpreted as being mediated by mass extinctions; that is, as a Type 4, noncompetitive adaptive radiation where mass extinction creates opportunities for faunal change by removing incumbent taxa, enabling other groups to undergo adaptive radiation. Examples include Late Ordovician brachiopods (Sheehan, 1982), Late Paleozoic mammal-like reptiles (Kemp, 1982), post-Paleozoic benthos (Gould and Calloway, 1980), Late Triassic ammonoids (Hallam, 1987), Late Triassic tetrapods (Benton, 1983), Late Cretaceous tetrapods (Russell, 1979), Late Cretaceous turtles (Rosenzweig and McCord, 1991), Late Cretaceous bivalves and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 27 Precambrian Paleozoic Mesozoic Cenoz. € I O I S I D I M l P | Pr Tr | J | K t | q Abundant Common Archaeogastropoda Mesogastropoda Neogastropoda Opisthobranchia Pulmonata Figure 13: Gastropod evolutionary history through the Phanerozoic (after Levin, 1999). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 28 gastropods (Jablonski, 1986), Late Cretaceous reef-builders (Sheehan, 1985), and Mid-Tertiary carnivorous mammals (Radinsky, 1982)). Other work focuses on the distinction between background extinction and mass extinction suggesting there is more than one way to produce faunal replacement (Jablonski, 1986). Particularly, many adaptations that were valuable during prolonged background extinction are indifferent during a mass extinction. Instead, environmental tolerances or geographic range become more necessary to mass extinction survival (Jablonski, 1986). Other workers agree that mass extinctions play a much larger role in faunal replacement then previously thought. For example, Simpson’s “Tempo and Mode in Evolution” clearly indicates that replacement occurs in the wake of mass extinction (Simpson, 1944). In addition, it is now clear that younger faunas do not displace older faunas. Instead, younger groups expanded after mass extinctions (Hallam, 1987). Furthering the ideas of Jablonski (1986), another study concludes that the privilege of incumbency (including substantial geographic range, large numbers of organisms, and heavy use of resources) prevents new taxa from gaining a foothold in the community (Rosenzweig and McCord, 1991). However, incumbency cannot prevent all extinction. Once extenuating environmental perturbations displace incumbents, for example, new species with the slightest local adaptation can better invade the empty niche. Once this novel species fills the vacated niche, natural selection takes over fine-tuning its life history according to its new environment. Origination rates therefore increase due to the advantage of incumbency. In sum, a number of major faunal replacements previously regarded as competitive, are now reinterpreted as having been mediated by mass extinctions (Benton, 1983; Gould and Calloway, 1980; Hallam, 1987; Jablonski, 1986; Kemp, 1982; Radinsky, 1982; Rosenzweig and McCord, 1991; Russell, 1979; Sheehan, 1982; Sheehan, 1985). This reinterpretation of replacement dynamics indicates Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 29 that mass extinction processes play an important role in shaping macroevolutionary patterns. Mass extinction processes, however, are not the only controlling factor driving faunal replacement; it is now clear that environmental and ecologic interactions are integral parts that shape macroevolutionary history (Valentine, 1973). Together these studies indicate that faunal replacement is more complex than two taxa competing for resources and space. Structure of Thesis Chapters 1 and 2 are general introductory chapters that describe the overall project in terms of its purpose, general background and statistical information. The main body of this thesis is divided into three chapters, each written to stand independently. Chapters 3 and 4 provide the data and statistical analyses needed for assessing paleocommunity structure. Chapter 5 deals with comparing statistical results between Paleozoic and Mesozoic communities and Chapter 6 discusses the overall conclusions on brachiopod and bivalve replacement. Chapters 3 through 6 present a full analysis of the specific topic each covers. The concluding chapter, Chapter 7, summarizes this dissertation and discusses possible future research directions that can stem from this study. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 30 Chapter 2: General Statistical Methods Data Acquisition When attainable, relative abundance data are known to include more information in a study compared to presence-absence data (Gauch, 1982; Rahel, 1990; Sneath and Sokal, 1973). Therefore, generic abundance data were compiled from primary literature sources, unpublished sources including PhD. dissertations and a summary literature source, a digital paleontological database called the Paleobiology Database housed at the National Center for Ecological Analysis and Synthesis (NCEAS) and associated with the University of California at Santa Barbara. This NSF-funded database is a collaborative data compilation project initiated by Dr. John Alroy, Dr. Charles Marshall, and Dr. Arnold Miller that is extremely unique because it provides locality-specific faunal inventories including geographic, environmental, and geologic data for each locality. Access to such a robust database proves invaluable because it allows one to analyze large numerical collections (i.e., 387,992 specimens used for this study) in a timely and cost efficient fashion. A large numerical collection, such as this, provides a critical resource that has the potential to answer questions concerning global, faunal patterns. The data used in this study includes faunal information from the Middle and Late Triassic (i.e., the early Mesozoic data) and the Pennsylvanian and Early Permian (i.e., the late Paleozoic data). The foundation of this thesis is centered on the early Mesozoic data while the late Paleozoic data serves as the constant or as an example of Paleozoic benthic communities from which we can compare early Mesozoic community structure. Specifically, the early Mesozoic data were compiled from primary literature and unpublished dissertations. Studies were selected based on their content, that is, those that record numerical counts of individual organisms and provide Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 31 sedimentological information and/or an environmental interpretation of the study area. To date, this early Mesozoic database incorporates all the known abundance data available in the literature. Once compiled, early Mesozoic data was entered into the Paleobiology Database for future diversity and paleoecological studies. Originally, I planned to collect data from the Luning Formation, Nevada and the Kossen Formation, Austria, two localities known for their abundant brachiopod associations. Upon further research, two unpublished dissertations, one for each location, were found to include sufficient taxonomic and sedimentological data for paleoecological study. Since these two dissertations comprise nearly 50% of the entire early Mesozoic data, each field area was investigated in detail. Taxonomic and sedimentological information provided in these two dissertations were confirmed by visiting specific sites, collecting specimens, and walking each outcrop to confirm environmental results. In addition, taxonomic identifications were confirmed by reviewing museum collections deposited by dissertation authors and other workers from those areas. Unfortunately, due to time and financial constraints, other Triassic localities used in this study (i.e. Cassian Formation, Italy; Kossen Formation, Italy; Val Palina, Italy; Upper Silesia, Poland; Zamostie limestone, Slovack Karst, Slovakia; Wetterstein limestone, Slovakia; Balaton Highland, Hungary; Qingyan, southwestern China) were not visited. However, because this remaining data resulted from the peer-reviewed literature, experts working in those specific areas agree on the results presented and results are thus taken for face value. Taxonomic identifications were confirmed by comparing photos from the primary literature synthesized with the latest systematic and environmental descriptions. All late Paleozoic data was collected directly from the Paleobiology Database. Data was chosen for use foremost because the studies recorded abundance data during a time interval before benthic communities were affected by the end- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 32 Permian mass extinction. All abundance records within the Paleobiology Database from the Late Carboniferous, Early Permian and Middle Permian data were originally compiled. Late Permian data were avoided because a mass extinction is thought to have occurred in the Late Permian before the end-Permian mass extinction (Stanley and Yang, 1994). Middle Permian data were deleted from this study because sample sized were too small for meaningful statistical analyses. Therefore, only Late Carboniferous and Early Permian data are analyzed. Late Paleozoic taxonomic identifications were also confirmed by comparison with photos from the primary literature as well as analysis of the latest environmental interpretations of the areas and systematic descriptions for each genus listed in the dataset. Statistical Background Quantitative paleoecologists, as well as modem ecologists, typically need to analyze the effects of multiple environmental factors on dozens (if not hundreds) of taxa simultaneously. It is not surprising, therefore, that paleoecologists employ a variety of multivariate approaches, borrowed from the modem ecologist, to analyze community data. Ordination and classification (or clustering) are the two main classes of multivariate methods that community ecologists employ. To some degree, these two approaches are complementary. Classification, or putting samples into (perhaps hierarchical) classes, is often useful when one wishes to assign names to, or to map, ecological communities. However, given the continuous nature of communities, ordination can be considered a more ‘natural’ approach (Gauch, 1982). Classification typically produces disappointing results when samples are arranged continuously along gradients. In this study, ordination techniques were employed to analyze this database. Considering that the goal of this research is to reveal the mechanisms underlying faunal relationships and that the main taxa in question are Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 33 two groups (brachiopods and bivalves) that tend to overlap in their environment and ecology, the general faunal associations are more continuous than not. For these reasons, ordination was elected as the most appropriate technique for this research. Ordination methods operate on a community data matrix (or taxa by sample matrix). A community data matrix has taxa as rows and samples as columns or vice versa. In community ecology, the term “sample” has diverged from its usage in statistics, and refers to the basic unit of observation. In this study, a sample is considered to be a collection of taxa from the same local area; that is, a collection of stratigraphic horizons from a particular location. The elements in community data matrices are taxonomic abundances. ‘Abundance’ is a general term that can refer to density, biomass, cover, or even incidence (i.e., presence/absence) of species. In this study, abundance refers to the numerical count of individual taxa, particularly at the generic level. Taxonomic composition is expressed in terms of relative abundance; that is, constrained to a constant percentage total per sample (i.e., 1 or 100%). As mentioned previously, ecologists typically grapple with dozens of dimensions (taxa and/or samples); therefore, another reason to employ ordination is that it helps visualize multiple dimensions simultaneously. Unlike classification (or clustering), ordination represents important and interpretable environmental gradients in low dimensional space and by focusing on these important dimensions, one avoids interpreting (and/or misinterpreting) noise. Thus, ordination is considered a ‘noise reduction technique’ (Gauch, 1982). The graphical results, usually two-dimensional in which similar samples or taxa or both are near each other and dissimilar entities are far apart, lead to a ready and intuitive interpretation of taxa-environment relationships. Numerous ordination methods have been put forward, but the only two techniques used in this study will be discussed. Ordination methods are divided Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 34 into two types: indirect and direct. Indirect gradient analysis positions sample units according to covariation and association among taxa while direct gradient analysis arranges sample units according to direct measurements of environmental factors (McCune, 1997). The differences between indirect and direct gradient analysis, while sometimes blurred in practice, are crucial (Gauch, 1982; ter Braak and Prentice, 1988). Indirect gradient analysis utilizes only the species by sample matrix. If there is any information about the environment, it is used after analysis, as an interpretative tool. When we perform an indirect analysis, we are essentially asking the taxa what the most important gradients are. It is entirely possible that the most important gradients are ones for which we have no external data, yet indirect analysis will take advantage of redundancy in the data set and display such gradients. Direct gradient analysis, in contrast, utilizes external environmental data in addition to the species data. Since environmental data is difficult to directly measure from the fossil record, paleoecologists tend to use indirect methods. In light of this, discussion on direct gradient analysis will end here and indirect methods will be explained further (e.g., Nonmetric Multidimensional Scaling and Detrended Correspondence). Non-parametric Multidimensional Scaling Analysis Nonmetric-Multidimensional Scaling (NMDS) is a distance-based ordination method that is well suited to data that are non-Gaussian or are on arbitrary, discontinuous, or otherwise questionable scales. My main interest in this technique lies in its properties to assess the dimensionality of a data set. An advantage of NMDS is that, being based on ranked distances, it tends to linearize the relation between environmental distance and taxonomic distance. NMDS is an iterative search for a ranking and placement of n entities on k dimensions (axes) that minimizes the stress of the ^-dimensional configuration (McCune, 1997). The Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 35 calculations are based on an n x n distance matrix calculated from the original n x /^-dimensional main matrix, where, for this study, n is the percent of samples and p is the percent of genera. “Stress” is a measure of departure from monotonicity in the relationship between the dissimilarity (distance) in the original /^-dimensional space and distance in the reduced ^-dimensional ordination space. Detrended Correspondence Analysis Detrended Correspondence Analysis (DCA) is an eigenanalysis ordination technique based on reciprocal averaging (RA). Like RA, DCA ordinates both species and samples simultaneously however, RA tends to plot its solution in an arch. The arch pattern that is almost inevitable with more than one dimension in RA is squashed with DCA. This is done by dividing the first axis into segments, then setting the average score on the second axis within each segment to zero. Another fault of RA, the tendency to compress the axis ends relative to the middle, is also corrected with DCA. This is accomplished by rescaling the axis to equalize as much as possible the within-sample variance of species scores along the sample ordination axis. Also like its parent technique, DCA implicitly uses a chi-squared distance measure. Contrast between DCA and NMDS DCA and NMDS are the two most popular methods for indirect gradient analysis. The reason they have remained side-by-side for so long is because, in part, they have different strengths and weaknesses. While the choice between the two is not always straightforward, it is worthwhile outlining a few of the key differences. Some of the issues are relatively minor: for example, computation time is rarely an important consideration, except for large data sets. Some issues are not entirely Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 36 resolved: the degree to which noise affects NMDS, and the degree to which NMDS finds local rather than global options still needs to be determined. Since NMDS is a distance-based method, all information about species identities is hidden once the distance matrix is created. For many, this is the biggest disadvantage of NMDS. Perhaps the biggest difference between the two methods is that DCA is based on an underlying model of species distributions, the unimodal model, while NMDS is not. Thus, DCA is closer to a theory of community ecology. However, NMDS may be a method of choice if species composition is determined by factors other than position along a gradient; for example, the species present on islands may have more to do with vicariance biogeography and chance extinction events than with environmental preferences - and for such a system, NMDS would be a better a priori choice. As De’ath (1999) notes, there are two classes of ordination methods - ‘species composition representation’ (e.g. NMDS) and ‘gradient analysis’ (e.g. DCA) (De’ath, 1999). The choice between the methods should ultimately be governed by this philosophical distinction. In this study, NMDS is used to analyze the entire data set, late Paleozoic and early Mesozoic data. Since the entire data set is largely segregated by biogeography and geological time, faunal patterns were investigated using NMDS. Once the dataset was broken down into their appropriate geological stages, faunal patterns were examined more rigorously by employing DCA; thus, searching for the underlying ecological gradient between specific localities within their appropriate geological stages. Multi-response Permutation Procedures (MRPP) Since NMDS and DCA are indirect analyses, they are considered “exploratory” and the job of the ecologist to use his or her knowledge and intuition Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 37 to interpret data (Gauch, 1982). To aid in this interpretation, a cross-validation approach by combining the exploratory analysis of ordination with the objective, hypothesis testing of a non-parametric procedure: MRPP is employed. MRPP tests the hypothesis that there are no differences between two or more groups. For example, one could compare species composition between pelagic and benthic associations to test whether or not the two different in faunal composition. Discriminant analysis and multivariate analysis of variance (MANOVA) are parametric procedures that can be used on the same general class of questions. However, MRPP has the advantage of not requiring the assumption of normality, which is rarely met with ecological community data (Biondini et al., 1985). The method requires that groups of entities (samples in the matrix) be defined a priori. Here, MRPP is used as a comparative measure to assess relative performance of different grouping variables. It is thus merely a tool supplementary to ordination that measures the difference among pre-categorized samples. Samples are grouped with secondary information, in this case: paleogeographic location, depositional environment, geological stage, taxonomic groups, substrate preference, and ecological niche. Searching for Patterns within Ordination Analysis General understanding A large portion of this research examines whether or not paleogeography, age and/or depositional environment influences faunal patterns. As a means to test this, statistical ordination techniques were employ as described above. In this case, the techniques search for redundancies within taxonomic relative abundance and plot samples according to the redundant similarity or differences between samples. Once the sample coordinates are plotted, if genera varied between two samples Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 38 one would expect those samples to plot separate from one another in ordinal space. Likewise, if two samples shared taxa the samples will overlap in ordinal space. This inherent behavior of sample placement lends itself to discovering overall controlling mechanisms driving faunal patterns by coding samples according to their paleogeography, age, and depositional environment. For example, if samples collected from a boreal region differ in taxonomic composition compared to samples from a tropical location, boreal samples would plot separate from the tropical samples. One could conclude from this plot that paleogeography is an important factor that influences faunal patterns. In contrast, if boreal samples plot in the same location as tropical samples (i.e., samples overlap), similar fauna occur in both locations and as a result, paleogeography is not a major factor influencing faunal patterns. Using this logic, once sample coordinates are calculated using ordination techniques, samples can be coded according to their specific paleogeography, age and depositional environment and then we can tell which factor controls sample placement by the amount of overlap exhibited between samples. In addition to coding samples, we can code taxa according to their appropriate ecologies. Since DCA (detrended correspondence analysis) calculates taxonomic and sample coordinates, the taxonomic coordinates can be coded in the same manor as samples; thus, we can test whether or not criteria such as substrate preference, feeding habit, and taxonomic groups (i.e., brachiopod versus bivalve) control faunal patterns. The next section explains how I differentiated samples and taxa into their appropriate categories. Sample categories Paleogeographic location was determined using ArcView (a Earth System Research Incorporate geographic information systems product), a complete, single, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 39 integrated software product for geographic data creation, management, integration, and analysis. Latitudal and longitudinal data were collected either from the original source publication and when that was not available, latitudal and longitudinal coordinates were estimated by searching the nearest town or cities using the following web sites: http://www.traveljoumals.net/search.asp and http://www.bcca. org/misc/qiblih/latlong.html. Once latitudal and longitudinal coordinates were determined for each outcrop, ArcView calculated paleolatitude and paleolongitude coordinates according to Late Carboniferous (300 Ma), Early Permian (280 Ma), Middle Triassic (240 Ma), and Late Triassic (220 Ma) reconstructions and produced paleogeographic interpretations with the outcrop locality plots for each time interval. For each time interval, the plotted outcrop locations were then grouped into regional areas according to their general regional environment and location (e.g.: Eastern Pacific realm, Northwest Tethys realm, Northeast Tethys realm, and Germanic Epicontinental Sea). Each publication recorded the age of the reported units. However, not all publications record absolute ages and many research papers relied on index fossils to place their fossils into a geological stage. Geological stage names were converted to their international equivalent according to the International Commission on Stratigraphy (ICS) for the purpose of consistency. In the subsequent review, the reported stage name is listed along with its ICS stage name used in this analysis. In addition to placing their fossil information into a geological time perspective, all publications recorded the primary lithology however some did not interpret a depositional environment. For those publications that did not estimate a depositional environment, a depositional environment was estimated based on the recorded primary lithology and other sedimentary characteristics (Figure 14). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 0 The following paragraphs review the detailed locality information, age, and environmental interpretations for each publication used in this database. Beginning with the Late Carboniferous, Beus and Lane (1969) recorded systematic information on the abundant brachiopods and one gastropod from the Bird Springs Formation near Indian Springs, Clark County, Nevada (Figure 15 - Note locality UCLA 4426 marked with an “X”). Beus and Lane (1969) place their collected fauna within the Desmoinesian stage (i.e., ICS stage: Moscovian) of the Late Carboniferous because Chonristites and the bryozoan Ascopora, each of which has been used to zone the Russian Moscovian, occur at this outcrop as well as the index fusulinid Fusulina (Figure 16). Also, based on the presence of two brachiopods, Fimbriaria and Calliprotonia, this locality is thought to correlate with the Moscovian of north-central Texas (Beus and Lane, 1969). Since this faunal data came from one locality and primarily from a packstone lithology, all taxa were lumped into one sample. No formal environmental interpretation was proposed in this paper; however, the last half-century of paleontologic and sedimentologic investigation by academic, government, and industry geologists concludes that the Bird Spring Formation records open-marine carbonate platform (ramp) deposition which is intergraded into the strata of the Midcontinent region (Cassity and Langenheim, 1966; Heath et al., 1967; Poole and Sandberg, 1991; Saltzman, 2003). Mudge and Yochelson (1962) and Olszewski (2001) studied the uppermost part of the Pennsylvanian of Kansas and Mudge and Yochelson continued into the lower part of the Permian sequences. The Late Carboniferous faunal data used came from each member within the Virgilian time interval (or ICS stage Gzhelian) (Figure 17). This stratigraphic interval reflects the well-known cyclothemic stratigraphy of the northern Midcontinent (Heckel, 1986; Miller and West, 1993; Mudge and Yochelson, 1962; Olszewski, 2001; Zeller, 1968). At this time of global Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 41 Land Open Carbonate Shelf Basin Inner Middle Outer V Interplatform basin Inner: Middle: Outer/Slope: Argillaceous Packstone, limestone, Wavy limestone, ' wackestone, dolomitic limestone bivalve coquina, 1 argillaceous bioclastic limestone, | limestone, Interplatform: bioclastic ■ argillaceous Limestone, wackestone shale, sandstone, marl/limestone, clay 1 biodetrial marl, 1 limestone, 1 bioclastic 1 limestone 1 3 Basin: Limestone, shale, wackestone, siltstone, cl ay stone/wackestone Figure 14: Schematic depicting depositional environmental categories. It should be noted that the interplatform basin environm ent occurs within the open carbonate shelf however not all carbonate shelf environm ents have interplatform basins. Listed are the original primary lithologies used to describe the fossil localities. Some primary lithologies cross over into different depositional environments depending on additional sedimentological characteristics described by the original authors. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 42 INDIAN SPR IN G S Mercury,Nev. 2 M I L E RANCH M m c Pbs. Mmc Mis Pbs Mis Figure 15: Location map for the Indian Springs location, UCLA locailty 4426 (after Beus and Lane, 1969). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 43 “icehouse” climatic conditions, an icesheet was present at the south pole leading to cyclical eustatic and climatic changes (Fischer, 1986; Ziegler et al., 1997). The Midcontinent region at this time had a shallow eperic sea, which covered much of the North American continent. Here, cyclicity occurs at two scales; at the finest scale resolution, meter-scale cycles occur in both open-marine, platform setting and nearshore, coastal setting (Miller et al., 1996; Miller and West, 1993; Olszewski, 2000). At the larger scale, (that of a classic cyclothem), composite depositional sequences, approximately 8 to 13 meter-thick, can be recognized (Miller and West, 1993; Olszewski, 2000). Open-marine carbonates, marine mudrocks, and condensed sections dominate the trangressive and early highstand phases while peritidal carbonates, deltaic sandstones, and pedogenic mudrocks dominate the late highstand deposits (Olszewski, 2001). Figure 17 depicts five complete (Roman numerals I- V) and two incomplete (Roman numerals 0 and VI), classic cyclothem composite sequences. Olszewski and Patzkowsky (2001) concluded that each composite sequence represents a re-establishment of similar marine environments on the platform. Therefore, within each publication faunal data were combined according to their similar lithologies because similar lithologies are thought to represent similar environments. For example, fossils from Mudge and Yochelson (1962) within a shale lithology were pooled into one sample and categorized into a deep, muddy basinal environment. Likewise, fossils from Olszewski (2001) within an argillaceous wackestone lithology were combined into one sample and categorized into a shallow, inner shelf subtidal environment. It should be noted that Mudge and Yochelson (1962) originally placed the Hughes Creek Shale in the Permian, but more recent data indicates that it is late Carboniferous therefore, the Hughes Creek Shale faunal data was reassigned to the Gzhelian ICS stage (Baars et al., 1994; Heckel, 1986; Olszewski, 2001; Zeller, 1968). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 4 4 ERM 290 Ma z < z < > > - CO z z UJ CL 325 Ma CL a CO CO co co S 350 Ma 1 B E 7 sta g e Wolfcamc zone WaffiTan lawman Desmoin- esian Atokan klap.-sinu t ul Morrow C hester c < 0 d ) o> co co O Kinderho Famen. Triticites Fusullna Fusulinel. 1 Protusul. convexus . basslen- symmet. M M = 03! jm vuricalus' Meramec (exanus me/?// anchoml. U . typicus L . typicus' Isosilcha Dawn CPT Figure 16: Generalized measured section for the Arrow Canyon Range succcession. The Beus and Lane (1969) fauna were collected from the Bird Springs Formation within the Fusulina zone of the Pennsylvanian, Late Carboniferous (after Saltzman, 2003). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 45 Members Formations Florena sh VI Beattie Ls Cottonwood Is o . Eskridge Sh Neva Is Salem Point sh V Burr Is Grenola Ls Legion sh Sallyards Is Roca Sh Howe Is IV Bennett sh Red Eagle Ls - 300 Ma Glenrock Is Johnson Sh Long Creek Is III Hughes Creek sh Foraker Ls Americus Is Hamlin sh Five Point Is Janesville Sh W est Branch sh Falls City Ls Hawxby sh Aspinwall Is O naga Sh Towle sh Brownville Is Pony Creek sh Grayhorse Is Wood Siding Fm Plumb sh o. N ebraska City Is French Creek Is Jim Creek Is Root Sh Friedrich sh Grandhaven Is Dry sh Stotler Ls Dover Is Pillsbury Sh Maple Hill Is 0 Zeandale Ls W amego sh Tarkio Is Figure 17: Mudge and Yochelson (1962) and Olszewski (2000) collected their fossil data from the members within this strati graphic column. Roman numerals denote com posite depositional sequences, I through V are com plete sequences. 0 and VI are partial sequences (after Olszewski and Patzkowsky (2001). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 46 The last Late Carboniferous data source is West (1970). West (1970) completed eight detailed stratigraphic sections within the Wewoka Formation from Hughes County, Oklahoma (Figure 18). Recent research concludes that the Wewoka Formation is of Desmoinesian age (i.e., Moscovian ICS stage) (West and Busch, 1985). West (1985) describes these sedimentary packages as meter- scale trangressive-regressive units similar to the cyclothem sequences of Kansas described above. These cycles are recognized features within the Pennsylvanian of the Midcontinent in outcrop and core (Miller and West, 1993). All faunal data used from this reference came from a homogenous “claystone” lithology, which has been interpreted as a deep, muddy basinal environment. Thus, all faunal data were combined into one sample. Early Permian references will be reviewed in the following paragraphs. Beginning with the west Texas fauna, the data utilized for study came from the Hess Formation within the Glass Mountains, Texas (Cooper and Grant, 1972-1977) (Figure 19). Due to the presence of a relatively continuously deposited section layer of Permian strata 1500 to 2000 m thick, the Glass Mountains represent the standard section for the Permian period extending from the Wolfcampian to late Guadalupian time. (Cooper and Grant, 1972-1977; Cromwell and Mazzullo, 1987; Ross, 1987). The Hess Formation (Hessian Stage, Lower Leonardian: ICS stage: Artinskian) comprises limestone depositional sequences that are well displayed in a carbonate- platform facies in the eastern Glass Mountains, where they have many parasequences and parasequence sets (Ross and Ross, 2003). Data were available from only one wackestone lithology therefore, fossil counts from this lithology were combined into one samples and interpreted as representing a muddy, basinal environment. Grant (1976) and Waterhouse (1982) studied the brachiopods of Thailand. Within the Rat Buri Limestone, faunal data were collected from Ban Kao, Khao Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 47 KANSAS AND NEBRASKA o > 2 ZMyrick S ta __ ~ Labette sh a le jHigg i nsv 11 le __ Lenopah Is. Altomont Is. Loberdie Is. Summit coal Hackjack I s . . Mulky coal ’Bevier coal' -AidiMr.e-l.SL Mineral cool Bluejacket ss. CENTRAL OKLAHOMA a ARKANSAS VALLEY Holdenvi11e Wewoka fm. Wetumka fm. Calvin ss. Senora fm. Stuart sh. Thurman ss. Tiowah Is. Inolo Is. Bluejacket ss. Spaniard Cr. Tamaha ss i k d l H Z o o (0 U J a: U J to to U J 2 O 2 to U J a Figure 18: Stratigraphic correlations of M oscovian, Late Carboniferous age sections. Fossils were collected from the Wewoka Formation, Hughes County, Oklahoma (after West, 1970). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 48 Phrik, Phangnga, and Ko Muk (northeast and northwest) (Figure 20) (Grant, 1976; Waterhouse, 1982). The full range of the Rat Buri Limestone (Group) remains poorly constrained, however, scientists believe it is likely to span from the Early Permian to Early Triassic (Shi and Archbold, 1998). Problems dating the Rat Buri Limestone stem from the poor taxonomic control and the long stratigraphic ranges of the faunas. However, the consensus at the present time places the Rat Buri Brachiopod Fauna in the Artinskian ICS stage (Fontaine et al., 1993; Grant, 1976; Sakagami, 1968; Shi and Archbold, 1995; Yanagida, 1970). For these references, faunal data were assembled into samples according to locality because each locality possessed a distinct lithological composition; after, each sample was placed into a depositional environment according the primary lithology of each site. The Ban Kao locality comprises a sandy, silty, limestone, in which Grant (1976) interprets as a fairly shallow, inner shelf environment with a firm substrate. The limestones of Khao Phrik and Ko Muk (northeast and northwest) contained little terrigenous material and has been interpreted as an middle shelf environment (Grant, 1976; Waterhouse and Sangat, 1970). The Palmarito fossil fauna of Venezuela has such a striking resemblance to the West Texas fauna that global correlations from West Texas are preferred over those based on Venezuelan faunas (Hoover, 1981). Hoover (1981) compared brachiopod generic composition within the Palmarito Formation to Permian biostratigraphic units within the West Texas regions. Results indicate that the highest levels of similarity lie between the Palmarito fauna and the Leonardian-aged West Texas fauna. Therefore, Hoover (1981) considers the Palmarito fauna to be within the Early Permian, Leonardian stage (i.e., ICS stage: Artinskian). The lithological character of this area consists of wackestone and has been interpreted as recording an basinal environment with soft, muddy substrates (Grant, 1976; Hoover, 1981). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 49 Age Formation Lithology Conodont zones J. xuanhanensis crofth J. prexuanhanensis J. ahudaensi> J. shannoni C a p ita n J. postserrata A ltu d a V id r io J. asserrata A p p el R a n c h W illis R a n ch J. nankingensis C h in a T a n k R o a d C a n y o n M. idahotnsis tambtrti C a th e d r a l M o u n ta in iV. sulcoplicatus M. siciliensis S k in n er R a n c h N. ? exscvlptvs L en ox H ills Strtpt. nevaensis Strept. Isolates N eal R a n c h Strept. elongates U d d em tes Strept. brownvillensis G a p ta n k Figure 19: Lithostratigraphic section of the Glass Mountains, Texas, USA. Hess Formation is located toward the bottom of the section within the Artinskian stage. Conodont zones are shown on the right (after Mei et al., 2001). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 50 LAOS NAM BURMA • Chlong Mai .rv. » Loei Soraburi > - '< Bangkok j A N D A M A N SEA C A M B O D IA GULF O F SIAM VIET NAM [ Phangngc 1 Ko Phukatisi? \ Ko Muk o S j fon8 L .'-'J \ M A LA Y SIA Figure 20: M ap of Thailand showing major roads. Fossils were collected from four localities: 1) Sab Kao, near Kanchanaburi; 2) Khao Phrik, near Rat Buri; 3) Ko Muk, an offshore island near Trang; and 4) Phangnga, just north the Trang (after Grant, 1976). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 51 Hoover (1981) collected all the faunal data from this lithology and environment; therefore, all the faunal data from this reference was pooled into one sample and placed within a basinal environment. Kues (1995) described the fauna from the Hueco Formation of the southern Robledo Mountains, Dona Ana County, New Mexico (Figure 21). This fauna comes from Wolfcampian (i.e., ICS stage: Sakmarian) clastic units, which are part of a cyclically deposited mixed marine and nonmarine sequence (Kues, 1995; Mack et al., 2003). Fusulinid assemblage comparisons between this New Mexico section and the type section of the Hueco Group in Texas and the faunas of the Neal Ranch Formation of the Wolfcampian stratotype section in the Glass Mountains of west Texas location confirm the Wolfcampian age (Cooper and Grant, 1972- 1977; Wahlman and King, 2002). Strata of the Hueco Group accumulated on a stable western margin of the Orogrande Basin (Greenwood et al., 1977; Jordan, 1975). Limestones accumulated during relative sea-level highstands in a shallow marine shelf environment. Clastic sediments were deposited during relative sea- level lowstands when there was strong clastic influx in a nearshore to terrestrial environment. (Krainer et al., 2003). Interbedded shallow-marine fossiliferous packstone and mudstone-siltstone in the lower part of the succession resemble fifth-order sequences in the Midcontinent, but also may represent parasequences or autocycles (Mack et al., 1988; Mack et al., 2003). All fossil information from this reference were combined into one sample because Kues (1995) collected all fossils from an argillaceous, shale lithology, which has been interpreted as shallow, inner shelf subtidal environment. Mudge and Yochelson (1962), as mentioned above, collected fossil associations from the lower Permian, Midcontinent of Kansas. Fossils from this study ranging the Wolfcampian (i.e., ICS Stage: Asselian) stratigraphic interval Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 52 Sonto Rito 0 Cookes 0 £Peloncillo Rong* .Animos (J ) M l*- Florida Mts. % Big Hatch*! M il A n d r e i Dona Ana Robltdo Mts Sacramento Mts. NEW MEXICO Figure 21: Location of Robledo Mountains, south central New Mexico (after Kues, 1995). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 53 of the Council Grove Group were utilized. Fossil collections represent each stratigraphic interval except the Glenrock and Howe limestone member, and Roca Shale Formation (Figure 17). The Late Carboniferous cyclic deposition mentioned above continues into the Early Permian Council Grove Group representing one composite third-order depositional sequence (1-10 m.y.). This composite sequence contains parasequences that represent a trangressive-regressive system (Boardman and Nestell, 2000; Olszewski and Patzkowsky, 2003; Pieracacos, 2000). Following the protocol for the Late Carboniferous fauna, fossils within similar lithologies were combined, that is, limestone, and shale, into distinct samples. Each sample was then categorized into a depositional environment based on its primary lithology: limestone units represent middle environment and shale units represent a deeper muddy, basinal environment. Waterhouse (1983) described brachiopod and molluscan species from the Tiverton Formation, Northern Bowen Basin, Exmoor, Queensland, Australia. Two ammonoid species from the lower part of the Tiverton formation at Homevale, northwest of Nebo, Queensland, indicate an Artinskian age because of their affinities with Artinskian species from the type areas of the Lower Permian in the Ural Mountains, Russia (Armstrong et al., 1967; Waterhouse, 1983). Waterhouse collected fossils from a fine sandstone lithology, therefore, all taxa were pooled into one sample, categorizing the sample as representing a shallow, inner shelf subtidal environment (Waterhouse, 1983; Waterhouse and Jell, 1983). Yancey and Stevens (1981) is the last Early Permian reference to be reviewed. Yancey and Stevens (1981) collected fossils from the Pequop Formation, which is subdivided into the lower Moorman Ranch Member, the middle, Summit Springs Member and an upper, Moorman Ranch Member (Bissell, 1964a). Particularly, Yancey and Stevens 1981) based the proposed Leonardian age (i.e., Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 54 Artinskian ICS stage) on the fusulinid zonation of Stevens (1979), which has been supplemented by corals. Many geologists (Bissell, 1964a) have discussed some of the principal stratigraphy and paleontology of the Pequop Formation (Bissell, 1964a, b; Steele, 1960; Stevens et al., 1979; Trexler et al., 2004). The Lower Permian strata are interpreted as having been deposited in an interior seaway much like the one described for the Midcontinent above. A general reconstruction of depositional environments can be viewed in Figure 22. Yancey and Stevens (1981) collected fossils from four general lithologies, a shelly limestone, an argillaceous wackestone, calcareous mudstone and siltstone, and wackestone. The faunal data contained within these four lithologies were combined into four samples and based on Yancey and Stevens interpretations, the shelly limestone was categorized into an middle shelf environment and all subsequent lithologies as belonging to a shallow, inner shelf subtidal environment. Triassic references will be reviewed in the following paragraphs. During the Middle and Late Triassic, an extensive eperic carbonate platform formed in the subtropical Tethys region of the present day Alps, which records strong lithologic cyclicity (Goldhammer et al., 1987; Goldhammer et al., 1990). In general, most sedimentary units represent a seismically controlled, shallow-water, carbonate platform or interplatform basin with mixed siliciclastic and carbonate deposits (Jadoul et al., 1992; Szulc, 1988; Tomasovych, 2004). A generalized schematic of the depositional environments can be viewed in Figure 14. Gaetani (1969) and Torti Angiolini (1997) studied the Southern Italian Alps. Fauna collected from these areas are considered Anisian because the fauna was collected in association with the ammonoids from the Anisian Nevadites Zone (Brack and Rieber, 1993; Fantini Sestini, 1996; Torti and Angiolini, 1997). Gaetani (1969) collected fossils from the Angolo Limestone of Guidicarie, Trento. The primary Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 55 IDAHO NEVADA UTAH MoHu*c-domlnoted Community LAND ANTLER BELT LAND \O pen Shelf .Communlt! Comm unit l*« Neor Short 4 0 KM SEA Figure 22: Generalized reconstruction of the Early Permian miogeosynclinal seaway in northeastern Nevada and northwestern Utah. Shoreline positions are stylized and show possible shoreline configurations in different areas. Fossils from this site were collected from the open shelf and nearshore environments (after Yancey and Stevens, 1981). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 56 lithology consisted of a nodular, micritic limestone, which has been interpreted as a middle carbonate shelf environment (Gaetani, 1969). Torti and Angiolini (1997) collected fossils from the Esino Limestone and one primary lithology, a subtidal limestone (Figure 23). The most common facies associated with this limestone are wackestone and mudstones which have been interpreted as a shallow, interplatform basinal environment (Jadoul et al., 1992). Thus, these fossils were pooled into one sample and interpreted as representing an interplatform basinal environment. Kaim (1997) collected fossils from Upper Silesia in the Holy Cross Mountains, Poland (Figure 24). Recent paleomagnetic studies of the Roetian and Muschelkalk deposits of southern Poland (Upper Silesia, the Holy Cross Mountains) present the first complete magnetic polarity scale obtained for the Middle Triassic of the northern Peri-Tethys area. This study includes a chronological correlation of the late Olenekian-Ladinian succession over the entire Peri-Tethys Basin(Nawrocki and Szulc, 2000). Within this Peri-Tethys Basin, Kaim (1997) collected fossils from the Decurtella decurtata Biostratigraphic Zone, which specifically is Pelsonian in age (i.e., ICS stage: Anisian, Middle Triassic). Only fossil data from two lithologies were incorporated, the crumpled-wavy limestone and, a thin shellbed termed the bivalve coquina. Fossils from each lithology were separated into two samples and categorized as an outer shelf marginal environments because both contain disarticulated, low to high fragmented valves which have been interpreted as single to composite tempestites (Bodzioch, 1985; Kaim, 1997). Kochanova and Michalik (1986) collected fossils from the Slovak Zamosite Limestone Formation, in particular the Jasenie and Raztoka Limestone Members (Figure 25). The Jasenie Limestone member Raztoka Limestone member contains ammonites associated with the Balatonites balatonicus Zone placing this member in the Upper Pelsonian (i.e., Anisian, Middle Triassic). Its conodont association Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 57 B reno Fm. C. Rosso U th o z o n e 5 , 6 H th o z o n a 4 U th o z o n e — B u c h e n s te in Fm. i P re z z o L im esto n e A ngolo L im esto n e (Ise rl t i d a l do 1 o s tones*) Figure 23: Stratigraphic scheme of the Middle Triassic formations within the Southern Alps of Italy. The numbers indicate lithozones 3 to 6 of the Esino Limstone. Fossils were collected from lithozone 4 (after Jadou et al., 1992). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 58 with the Kockeli Zone (Papsova and Pevny, 1982) confirms this assignment. The Jasenie Member consists of a dark-grey argillaceous biomicrite limestone. Similarly, the Raztoka Member consists of a similar dark grey to light ash grey biosparite to biomicrite limestone. Therefore, the fossils from the two limestone members were combined into one sample and interpreted as representing a shallow, interplatform basinal environment. Palfy (2003) and Voros and Palfy (1989) both studied the classic Anisian faunas from the Balaton Highlands, Hungary. In these two studies, fossils were collected from the Felsoors Limestone Formation within four localities, Aszofo, Felsoors, Koveskal, and Vaszoly (Figure 26). Middle Triassic stratigraphy of this area records the disintegration of the uniform, Megyehegy Dolomite, an Early Anisian carbonate platform setting (Palfy, 1990). By the Late Anisian, deposition of laterally interfingering facies of patch reefs (Tagyon Limestone) and shallow basins with slopes (Felsoors Limestone) within the persisting fragments of the old platform (Megyehegy Dolomite) reflect the tectonic activity related to a rifting phase in the western Tethys (Galacz et al., 1985; Palfy, 1990). The Felsoors Limestone Formation is dated as upper Anisian, Middle Triassic. This age is confirmed by the preservation of ammonoids associated with Avisianum Zone (upper Anisian stage interval) (Voros and Palfy, 1989). Fossil data from each locality in Palfy (2003) was collected from different lithologies. The Aszofo fossils came from a predominantly limestone lithology, the Felsoors fossils from a micritic limestone, and the Koveskal fauna from a biodetrital limestone (Palfy, 2003). Fauna within each of these lithologies were placed into specific samples and categorized into depositional environments. The Aszofo limestone fauna was interpreted as a middle carbonate environment, the Felsoors finer grained limestone was interpreted as a lower energy, interplatform basin environment, and the Koveskal course-grained biodetrital Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 59 Stage | S u b s ta g e | 1 ) Sill L ith o lo g y a n d L ith o str a tig r a p h y (according to A n n u m ) 1944 an d S zu lc 1993) 8 D e p th c u r v e (alter Szulc 1993) r e la tiv e s h a llo w in g d e e p e n in g D ep o sitio n a l E n v iro n m en t (a n e r S zu lc 1993) Seq u en ce S tra tig ra p h y of th e Silesian M u sch elk alk (• tie r Szulc 1993) 1 a K e u p e r \ R e d b e d s 1 L ST I i alavus B o r u s to w ic e B e d s C o a s ta l s a b k h a ) • H S T J u . to enodis in n e r — i- t 1 B e d s R e s tr ic te d r a m p T ST ' < — i— -t _ m id — [ ’ ’ “ A j I — T h m o w ic e R e s tr ic te d in n e r r a m p M id d le ■ » S '5 M u sch elk a lk In te r v a l ____iy i a Judicarites a n d Neoschizodus D ip lo p o r a B e d s M id r a m p L ST orbicularis K a r c h o w lc e P a tc h r e e f b e lt of m id /o u te r r a m p B e d s ' 1 Decurtella • 1 * 1 • 1 - ,HSTc - K * **. •W w - 1 lilS ; ife t a t i p p * * • v ^ n 7 \ G d r a z d ie B e d s of o u te r r a m p O p e n o u te r r a m p T S T — ......... Myophoria vulgaris, Beneckeia buchi a n d Dadocrinus — . i i r r ^ L ST / 1 I n n e r r a m p O p e n , m id r a m p R e s tr ic te d in n e r r a m p .1 1 § m G o g o lin B e d s 1 H ST T ST 5 — r 5- ! " 1 DU C o a s ta l s a b k h a L S T A llut-ii 1 Figure 24: Stratigraphy and evolution of the Silesian M uschelkalk Basin, Poland. Highlighted area denotes the Anisian, Terebratula Beds from which fossil collections were made (after Kaim, 1997). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 60 pale gray stylolitized che_rty_ [sj± _ "bedded Is with stratiform cherts th ic k -b e d d e d gray m icritat lim estone with nodular bedding p la n e s , pea-like cherts and m arly laminae gray calcarenites & crin o i- dal b io s p a r ite s with o c c a s io n a l diagonal bedding 'thick-bedded calcarenite with Spongelio- black gray biom icrite with abundant s ilic ifie d fo s sils * ash-gray d o lo sp a rite -d o lo a re n ite m e g a b r e c c ia o f lim e sto n e a n d dolomite blocks in marly d o lo m icrite m a trix Figure 25: Schematic lithostratigraphic division of the M iddle Triassic carbonate complexes underlying the Reifling Limestone in the Choc nappe, the southern slope o f the Nizke Tatry M ountains (after Kochanovd and Michalik, 1986). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 61 limestone was interpreted as a higher energy, inner carbonate platform environment. Fossil data from two lithologies within the Vaszoly section of Voros and Palfy (1989) were obtained, a dolomitic limestone and biodetrital limestone. Fossils from these two lithologies were categorized into two separate samples. The dolomitic limestone sample was interpreted as a middle carbonate platform environment and the course-grained biodetrital limestone sample as a inner carbonate environment. The last Middle Triassic data comes from Stiller (2001). Stiller (2001) collected extensive faunal data within the Leidapo Member of the Qingyan Formation. These particular outcrops, located in southwestern Guizhou, China, consist mainly of mudstone, shales, and marls and are interpreted as representing carbonate platform, bank, and siliciclastic basinal deposits (Enos et al., 1997; Komatsu et al., 2004; Stiller, 1997). The shallow-water carbonate platform, named the Yangtze Platform, was a stable paleogeographic feature from the Late Proterozoic through the Triassic (Enos et al., 1997) and consists of basin-floor and slope deposits. Stiller (2001) recorded fossils from four general lithologies: claystone, claystone/ wackestone, claystone/marl, and marl. Fossils from the claystone and claystone/ wackestone lithologies were combined into one sample. These massive, laminated claystones/wackestones contain thin marl beds and have been interpreted as being accumulated on a basin floor (Figure 27). Therefore, it has been placed in the basin environment (Figure 14). The claystone/marl fauna were placed into one sample; this lithology is characterized by a matrix supported shell concentration that shows minor overturned folds and flame structures (Komatsu et al., 2004; Stiller, 2001). The marl lithology is characterized as a shell supported muddy calcarenite. The graded and massive beds contained abundant coarse bioclasts; therefore, fossils from these lithologies were combined into two separate samples and interpreted as being from a outer carbonate shelf/slope environment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 62 V a a z p rtm Marl F N am aavim oa Lat.F. B uchanilatnF. S T a a y o n T >lVlF< F i l i i t n U t.F . l»iK «h«av L it. F Figure 26: Lithostratigraphic scheme of the Middle Triassic and adjacent formations of the Balaton Highlands, Hungary. Fossils were collected from the Felsoors Limestone Formation (Fels5ors Lst. F.) (after Palfy, 1990). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 63 Late Triassic data sources will be reviewed in the following paragraphs. Fiirsich and Wendt (1977) explore the renowned Mesozoic strata of the Cassian Formation of the Central Dolomites, Southern Alps (Figure 28). Most of the Cassian Formation research focuses on the taxonomy of the fauna, however, recent chronostratigraphic studies confirm a Camian age (Late Triassic) (Mastandrea et al., 1997; McDowell et al., 1991). These strata represent deposition within interplatform basins between carbonate build-ups and locally in back-reef environments (Fiirsich and Wendt, 1977; Wendt and Fiirsich, 1979). Fiirsich recorded fossils from two lithologies, marl/claystone and packstone; the faunal from each lithology were combined into two samples and the marl/claystone samples were categorized into an interplatform basin environment while the packstone samples were placed into the middle carbonate platform environment. Golebiowski (1989) reconstructed the complex sedimentary and stratigraphic history of the Kossen Formation within the North Calcareous Alps, Austria and confirmed that the Kossen is separated into the Norian and Rhaetian stages of the Late Triassic. The Kossen Formation is differentiated into the Hochalm and Eiberg members, which are further separated into distinct units (Figure 29). Golebiowski (1989) collected fossils from a variety of lithologies but only the fossils from three lithologies were used and subsequently combined into samples according to the following lithologies: a calcareous, clay marl, bioclastic limestone, and subtidal limestone. According to Golebiowski (1989), the clay marl lithology represents an interplatform basin environment; the course-grain bioclastic limestone represents an inner platform environment, and the subtidal limestone, a middle carbonate platform environment (Figure 30). Hogler (1992) studied the Upper Triassic Luning Formation of Nevada (Figure 31). Silberling (1959) confirmed that the Luning Formation straddles the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 64 Fades Uthofades Environments Facies 1 Shell supported shell beds overlain by paralleMaminated mudstone (Turbidite) Facies 2 W M Matrix supported shell beds overlain by parallel-laminated mudstone (Debris flow deposits) Slope Facies 3 i P l Slump mudstone Facies 4 Massive and laminated thick mudstone with Posidonla Basin Figure 27: Lithofacies descriptions of Leidapo member, Qingyan Formation within the northern part of the M iddle Triassic Nanpanjiang Basin, China. Facies codes distinguished by Komatsu et al. 2004. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 65 HA UPT DOLOM IT N O R IA N c "O - I RA IB l FM TJ T O C A S S I A N FM CARN IAN 7 0 — > SCHLERN \ W E N G E N FM % CA \ VOLC A N ICS LADINIAN u o CO --------' ’T u CHENSTEIN FM m n SERLA DOLOMITE AN ISIAN Figure 28: Stratigraphic position of the Upper Triassic, Cassian Formation and the neighboring carbonate platform (Scherln Dolomite) (after Fursich and Wendt, 1977). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 66 Camian-Norian boundary of the Late Triassic. Subsequent collections of ammonites and halobiid bivalves confirm this age range (Kristan-Tollman and Tollman, 1983; Silberling, 1959). Within this regional area, Laws (1982) studied the fauna of the Upper Triassic Gabbs Formation (Figure 32). The Gabbs Formation, which overlays the Luning Formation, is exposed in the New York Canyon area of the Gabbs Valley Range (Laws, 1982). Researchers correlated the Gabbs Formation using ammonoid biostratigraphy and concluded that the formation is Norian (Late Triassic) in age (Silberling and Tozer, 1968; Tozer, 1979). Both the Luning and Gabbs Formation represent tectonically dismembered Lower Mesozoic carbonate platform complex (Silberling et al., 1987). The Luning Formation comprises a heterogeneous mix of siliciclastic and carbonate rocks that have been deformed by repeated episodes of faulting and folding. The Luning Formation represents two distal carbonate settings, an outer shelf/slope environment and a basin environment (Hogler, 1992). The outshelf/slope environment consists of whole fossil and bioclastic wackestones with interbedded shales and mudstones restricted to silts and clays. Fossils from this lithology were pooled together into one sample and placed into the outer/slope environment (Figure 14). The central part of this Luning section displays carbonate basinal features (Hogler, 1992). Lithologies such as lime mudstone, cliff forming lime mudstones, and lime mudstone/wackestone are present. These thinly laminated beds had little bioturbation and fossils were concentrated on single bedding planes. Fossil from these lithologies were placed into three separate samples and all samples were interpreted as being deposited in a basinal environment. The fossil data from the Middle Member of the Gabbs Formation was pooled into one sample (Laws, 1982). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 67 O •o o ion o o c = i= » 1 0 0 j— P l a t t e n k a l k Figure 29: Litholostratigraphy and facies of the Upper Triassic, Kossen Formation, Austria. Fossils were collected from the Holcham and Eiberg Members (after Golebiowski, 1990). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 6 8 i P n W m Kbrallenkalld- Bereich Dachsteinkalk LumacheUen- Bereich Detritus-Schlammkalk Bereich Holcham Member Eiberg Member Figure 30: General interpreted environments of the Upper Triassic, Kossen Formation, Austria. Each block corresponds with units within members. Local lithofacies zones are noted above the unit numbers (after Golebiowski, 1990) Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 69 A O E U T H O U O O Y LOCALITY z < D C o z E § E s s s S s & s a s -- z < z D C < o E s C M E o ft 11227 1122* 1 1 2 2 $ 11224 11223 11222 1 1 2 2 1 11220 1 1 2 1 0 11210 11217 11210 11210 11214 11213 1 1 2 1 2 1 1 2 1 1 1 1 2 1 0 11207 11200 11206 W 11202 11201 11200 11100 11100 11107 11106 11100 CO C M r ^ K i Figure 31: Lithostratigraphic section of the Upper Triassic, Luning Formation, Nevada. Positions of fossil samples are listed as "locality" numbers (after Hogler, 1991). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 70 * - I! i* S i D-7336 (TH R U ) D-7330 '--0-7347 0-7329 \ ^0-7346 PN>7327 w>- V ( A d f * '• ^0-7326 Dv3f6 ITH kuj 5^07309 : 1 THRU) N >7305 07353 07354 Figure 32: Com posite section through the Upper Triassic, Gabbs Formation, Nevada. Sampled intervals are listed to the right of the stratigraphic column (after Laws, 1982). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 71 The Middle Member generally comprises a calcarenite packstone facies. Laws (1982) interpreted this lithology as indicative of a non-agitated middle shelf environment with a soft bottom rich in organic mater. Thus, this sample was placed in a middle carbonate environment. The last Late Triassic data source is Siblik (1986). This study records Camian brachiopod associations from the Tisovec Limestone within the Slovak Karst area of Southeast Slovakia (Siblik, 1986). This West Carpathian section corresponds to the Middle Tuvalian-Subbullatus Zone making this section Camian in age (Late Triassic). Like most of the Tethys region or West Carpathian regions in the Middle and Late Triassic, this area has been interpreted as belonging to a carbonate platform environment (Krystyn et al., 1990). The Siblik fossil data was combined into one sample because the primary lithology for the fossil units is limestone, which is characteristic of a middle carbonate environment. Faunal categories Genera were classified into three categories: major taxonomic group (i.e., brachiopod and mollusc), substrate preference (i.e., infaunal or epifaunal), and ecological niche (combination of feeding and living habit). All genera were categorized into one of these eight ecological categories: 1) burrowing deposit feeder; 2) burrowing suspension feeder; 3) cementing suspension feeder; 4) endobyssate suspension feeder; 5) epibyssate suspension feeder; 6) epifaunal grazer; 7) pedunculate suspension feeder; and 8) reclining suspension feeder. Systematic classification and life habits were determined using the following references: (Bieler, 1992; Carlson, 2001; Carlson and Leighton, 2001; Carter et al., 2000; Carter et al., 1994; Chase, 2002; Cox and Newell, 1969; Grant, 1981; Hautmann, 2001; Knight et al., 1960; Kondo, 1998; Linsley, 1978; Michalik, 1977; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 72 Miller, 1990; Peck, 2001a, b; Pojeta, 1980; Pojeta et al., 1987; Rowell, 1981; Rowell and Grant, 1987; Rudwick, 1970; Savage, 1996; Schneider, 2001; Skelton et al., 1990; Stanley, 1968, 1970, 1972; Steiner and Hammer, 2000; Thayer, 1981; Williams et al., 1997; Williams et al., 2000; Yin and Yochelson, 1983a, b; Yin, 1983) Once categorized, specialist on brachiopods and bivalves reviewed the faunal lists and made any appropriate corrections. Dr. Michael Sandy and Dr. Sandy Carlson reviewed Paleozoic and Mesozoic brachiopods while Dr. Steven Stanley and Dr. Christopher McRoberts review Paleozoic and Mesozoic bivalves. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 73 Chapter 3: Early Mesozoic Brachiopod Resurgence: A case study of Middle and Late Triassic Brachiopod Paleocommunities. Abstract Brachiopod and bivalve dominated fossil assemblages from the marine Middle and Late Triassic of North America, Europe and China were analyzed. Using bulk samples, the study explores quantitative patterns recorded by the marine benthos including implications for paleogeography, depositional environment (along an onshore-offshore gradient), stratigraphic position, taxonomic groups (brachiopod or mollusc), substrate preferences, and ecological niches. A total of 21,671 genera were pooled from primary and summary literature resources. A total of 24 samples were analyzed from carbonate platform environments within Nevada, Italy, Austria, Poland, Slovakia, and China. Samples were categorized into paleogeographic location, depositional environment, and age. All specimens were identified to the genus-level and classified in terms of their taxonomic membership, substrate preference, and ecological niche. Relative abundance data were analyzed using detrended correspondence analysis (DCA) and multi-response permutation • procedure cross-validated the a priori categories (i.e., paleogeography, depositional environment, stratigraphic position, and specimen ecology). Multivariate analyses indicate that group membership (i.e., brachiopod or molluscs), substrate preference, and generic ecological categories controlled Middle and Late Triassic faunal patterns most significantly. To a lesser extent, paleogeographical location played an important role in sample distribution. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 7 4 Introduction As a paleontologist, when one hears the word “brachiopod” we immediately think “Paleozoic” and for good reason. During the Paleozoic, brachiopods dominated benthic marine communities with their great abundance, widespread distribution and explosive diversity trends. After the end-Permian mass extinction brachiopod stocks diminished dramatically and bivalve faunas replaced them as modem day dominants. The vanquished incumbents did not just retreat from the bivalve onslaught after the end-Permian mass extinction. Interestingly, when diversity patterns are considered further, brachiopods seem to rediversify after the end-Permian mass extinction. Global taxonomic diversity analyses show an increase in brachiopod diversity during the Middle and Late Triassic (Hogler, 1992; Kidwell, 1990; Sepkoski, 1996). Using Gould and Calloway’s diversity data, which originated from the Treatise of Invertebrate Paleontology, the radiation becomes apparent (Figure 6). Sepkoski’s research also displays this diversity pattern (Sepkoski, 1976; Sepkoski, 1996). More detailed studies indicate that brachiopods are in fact both diverse and abundant in Mesozoic rocks, especially in shallow marine environments (Ager, 1973, 1986, 1988; Michalik, 1987). Numerous papers document the biostratigraphic distributions of Mesozoic brachiopods as well as their specific occurrences and systematic descriptions within an area (Ager et al., 1978; Ager and Westermann, 1963; Benatov, 1997; Benatov, 2001; Campbell, 1990, 1994; Chen, 1983; Dagys, 1993; Fiirsich and Wendt, 1977; Gaetani, 1969; Gupta, 1984; Hoover, 1991; Iordan, 1975; Kaim, 1997; Kochanova and Michalik, 1986; Kochanova and Pevny, 1982; Marden etal., 1987; Michalik, 1977; Michalik, 1987; Palfy, 1990; Pevny, 1988; Sandy, 1994, 1995, 1997b; Sandy and Aly, 2000; Sandy and Blodgett, 2002; Sandy and Stanley, 1993; Senkowiczowa and Popiel-Barczyk, 1996; Siblik, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 75 1983; Skwarko et al., 1976; Stanley, 1994; Stanley et al., 1994; Sun, 1979; Sun and Ye, 1982; Tamaro and Sartori, 1996; Teichert et al., 1970; Torti and Angiolini, 1997; Tumsek et al., 1999). Still, detailed paleoecological analysis of Mesozoic brachiopod associations, including all major benthic taxa from a wide range of paleogeographic areas, has not been completed. Michalik (1987) expressed the need for such an analysis. As he states, “The process of mutual replacement of ecological equivalents in benthic marine communities is well detectable with use of the quantitative structural schemes. However, such a task supposes numerous complete series of analytic data on community structure in wide areas” (Michalik, 1987 p. 40). The type of collections mentioned above have now become available. This study compiles data from primary and summary literature to analyze approximately 21,671 specimens from shallow marine environments within equatorial regions of the Middle and Late Triassic. This study aims to reveal the underlying causal mechanism for faunal distributional patterns during this time. Study Areas and Geological Setting This study focuses on four marine provinces that existed throughout the Middle and Late Triassic: the Eastern Pacific Realm, the Northwestern Tethys Realm, the Northeastern Tethys, and the Germanic Basin. Figure 33 depicts these provinces in their paleogeographic context within tropical and subtropical climatic zones. Data sampling concentrated on the Anisian, Ladinian, Camian, Norian and Rhaetian stages within the Triassic (Figure 34). Data were analyzed from these stages according to their period divisions, that is, Middle Triassic and Late Triassic groups (Gradstein, 2004) (Figure 34). The overall geological setting consists of a series of trangressive/regressive phases. Long term sea-level changes indicate that a major transgression took place Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 76 A M iddle T riassic - 240 M a G erm anic Northeastern Epicontinental Tethys Sea Northwestern Tethys B Late T riassic - 220 M a Northwestern Tethys E a s te r n P a c ific Figure 33: Middle and Late Triassic global paleogeography. (A) Middle Triassic samples; Location A, the Germanic Epicontinental Sea Realm, combines data from Kaim (1997); Location B, the Northeastern Tethys Realm, combines data from Stiller (2001); Location C, within the Northwestern Tethys Realm, consists of data from Torti and Angiolini (1997) and Gaetini (1969); Location D, also within the Northwestern Tethys Realm consists of data from Kochanova and Michalik (1986), Palfy (2003), and Voros and Palfy (1989); (B) LateTriassic samples; Location A (Laws, 1981) and B (Hogler, 1991) are within the Eastern Pacific Realm; Location C (Fiirsich and Wendt, 1977; Golebiowski, 1991; Tumsek et al., 1999) and location D (Siblik, 1986) are within Northwestern Tethys Realm. Arrows in the Late Triassic map represent the supposed direction of brachiopod migration (after Ager, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 77 Geochronology Short term sea-level change (after Embry, 1988) Stratigraphic position of samples according to paleogeographic realm NE Tethys NW Tethys GES* Pacific Rise Fall 205 Sil G6 G2 G1 210 H4 H3 221 Si2 H2 228 Tol Kol 234 P2 V3 PI V2 Gal P3 Ka3 Kal 242 248 Perm. Figure 34: Geochronology from Early Triassic through Late Triassic (after Gradstein et al. 2004). Samples are categorized according to their appropriate stage and paleogeographic realm. Samples within stages are not arranged in stratigraphic order. *GES - Germanic Epicontinental Sea Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 78 in the coastal areas during the Anisian, which peaked in the Ladinian and began to regress during the Norian extending through Rhaetian (Dagys, 1993; Haq et al., 1987; Michalik, 1987). General ocean circulation reconstructions and taxonomic occurrence patterns indicate that free migration occurred along the northern Tethys, into the Germanic Basin, and occurred from the eastern Tethys to the New World via the Boreal regions (Figure 33). The low latitudes of the eastern Pacific record occurrences of particular genera from Siberia and Alaska confirming that free migrations occurred (Ager, 1988; Dagys, 1993). More specific geological information will be discussed according to specific regions. Eastern Pacific Realm The Eastern Pacific realm extends along the margins of western North and South America (Figure 33). The samples collected for this study are from the Late Triassic of the Western United States. In this region, Late Triassic rocks belong to various displaced terranes, which were accreted onto the North American continental via plate tectonics (Hallam, 1986; Sandy and Stanley, 1993). Appropriate data was available from two local areas: the Gabbs Formation and the Luning Formation of Nevada (Hogler, 1992; Laws, 1982). Other researchers presented data from this realm, however, this data was either unattainable or sample sizes were not sufficient for meaningful statistical analysis (i.e., > 200 specimens per sample) (Gonzalez- Leon et al., 1996; Goodwin, 1999; McRoberts, 1997; Sandy, 1994; Sandy, 1997a; Sandy and Blodgett, 2002; Stanley, 1997; Stanley et al., 1994). The sediments from these areas represent an open shelf carbonate platform environment ranging from nearshore to basinal settings. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 79 Germanic Epicontinental Sea Realm The Middle Triassic marks a time of major global transgression (Haq et al., 1987). As a result, epicontinental seas formed, particularly in the northern part of the Tethys Sea. Researchers refer to this area as the Germanic Basin or Muschelkalk Sea (Kaim, 1997). During the Middle Triassic, the Muschelkalk Sea connected to the Tethys Sea to the south and therefore, some fauna are shared between the two areas (Kaim, 1997; Pevny, 1988). For the purpose of this research, this area is termed the Germanic Epicontinental Sea realm. Data from this region comes from the Upper Silesia of Poland (Kaim, 1997). Paleogeographically, these field sites sat on the southern margins of the Germanic Basin. By the Late Anisian (Middle Triassic), tectonic activity transformed the once uniform carbonate platform into a combination of small, shallow interplatform basins within the old platform (Galacz et al., 1985). Northwestern Tethys Realm The Northwestern Tethys realm contains the most renowned Mesozoic strata due to their extremely diverse, excellently preserved invertebrate fauna (Fiirsich and Wendt, 1977). This particular realm contains data from the Middle Triassic (Gaetani, 1969; Kaim, 1997; Kochanova and Pevny, 1982; Palfy, 2003; Stiller, 2001; Torti and Angiolini, 1997; Voros and Palfy, 1989) and Late Triassic (Fiirsich and Wendt, 1977; Golebiowski, 1989; Hogler, 1992; Laws, 1982; Siblik, 1998; Turnsek et al., 1999). Classic monographs from the late 1800’s record the first synopsis of the different subtropical Triassic brachiopods from the Mediterranean region (Bittner, 1891). Subsequently, numerous researchers published information regarding brachiopod associations from the area (Ager, 1965; Ager, 1967, 1971; Pevny, 1988; Tamaro and Sartori, 1996). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 80 The references utilized in this study are listed and described according to their well- known regional categories (i.e., West Carpathian, Northern Calcareous Alps, and Southern Alps). The West Carpathian (Slovakia) carbonate platform was situated at the northwestern margin of the Tethys Sea (Michalik, 1994; Tomasovych, 2004; Tomasovych and Farkas, 2005). The extensive, shallow interplatform basinal environment is quite similar to that of the Upper Triassic (Rhaetian) Kossen Formation, which is also included in this study (Golebiowski, 1991; Tomaovsch, 2004). Specifically, data reported from Kochanova and Michalik (1986) contains macrofauna from the Slovak Zamosite Limestone Formation, Jasenie and Raztoka Limestone Member. During the Late Triassic, the Northern Calcareous Alps represented an extensive carbonate platform situated on the western margin of the Tethys Sea (McRoberts et al., 1997; Ohlen, 1959; Piller, 1981). Primarily, the data incorporated in this study is from the Kossen Formation. These strata record a regressive carbonate succession within a muddy interplatform basinal environment separated from the open ocean to the east by an extensive carbonate platform (e.g. Dachstein Limestone) (Golebiowski, 1989; McRoberts et al., 1997; Tumsek et al., 1999). Geochemical analyses within the Kossen Formation were conducted and it is concluded that upper Kossen carbonates were deposited in shallow, normal marine conditions with water temperatures ranged from 18-24° C (McRoberts et al., 1997; Tumsek etal., 1999). The references compiled from the Southern Alps of Italy and Hungary document Middle and Late Triassic time periods (Fiirsich and Wendt, 1977; Gaetani, 1969; Palfy, 2003;Torti and Angiolini, 1997; Voros and Palfy, 1989). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 81 Data compiled from the Bergamasc Alps, Italy includes Torti and Angiolini (1997) and Gaetani (1969). Both studies analyze the Middle Triassic Esino Limestone and record carbonate platform facies. The Middle Triassic stratigraphy of Hungary records the disintegration of the uniform, Megyehegy Dolomite, an Early Anisian carbonate platform setting (Palfy, 1990). By the Late Anisian, deposition of laterally interfingering facies of patch reefs (Tagyon Limestone) and shallow basins with slopes (Felsoors Limestone) within the persisting fragments of the old platform (Megyehegy Dolomite) reflect the tectonic activity related to a rifting phase in the western Tethys (Galacz et al., 1985; Palfy, 1990). Fiirsich and Wendt (1977) studied the Late Triassic Cassian Formation. Similar to the Northern Calcareous Alps, the fossils from these areas are from shallow, interplatform basins between carbonate build-ups (Fiirsich and Wendt, 1977; Gaetani et al., 1981; Gaetani and Jadoul, 1979; Jadoul et al., 1992). Northeastern Tethys Realm Data for the Northeastern Tethys realm comes from only one reference within the Middle Triassic (Stiller, 2001). Stiller (2001) collected extensive faunal data within the Leidapo Member of the Qingyan Formation. These particular outcrops, located in southwestern Guizhou, China, consist mainly of carbonate platform, bank, and siliciclastic basinal deposits (Enos et al., 1997; Komatsu et al., 2004; Stiller, 1997). The shallow-water carbonate platform, named the Yangtze Platform, was a stable paleogeographic feature from the Late Proterozoic through the Triassic (Enos et al., 1997). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 82 Triassic Brachiopod Diversity and Distribution Patterns Beginning at the end of the Permian, mass extinction wiped out the bulk of the Permian genera, for example, most impunctate spiriferides, chonetids, productids, dictyonellides, orthotetides, and orthides (Cooper, 2001). However, Paleozoic brachiopod taxa survived in several world regions into the earliest Triassic (Hoover, 1979; Kummel and Teichert, 1970; Liao, 1980; Michalik, 1987; Nakazawa et al., 1975; Schubert and Bottjer, 1995). Early Triassic brachiopod faunas still remain unclear but the majority of the impoverished, low-diversity faunas (i.e., five genera) inhabited the northern shore of the Tethys Sea and in low paleolatitudes of the eastern Pacific (Dagys, 1993). The Griesbachian and Dienerian stages brought further brachiopod repopulation to the central part of the Tethys (Ager, 1971; Dagys, 1993; Sandy, 2001). Simple non-specialized types represent the fauna, which appear to be examples of disaster taxa or opportunistic taxa (Alexander, 1977; Liao, 1980; Michalik, 1987; Rodland and Bottjer, 2001) During the Middle Triassic, rhynchonellides, spiriferides, terebratulides, and athyridides rebounded to moderate diversity levels in terms of species numbers and morphological variability (Sandy, 2001). During the Anisian, brachiopod diversification accelerated to approximately fifty genera (Dagys, 1993). Despite this diversification, brachiopod distributions were still mainly limited to the northern shore of the Tethys; however, occasional immigrants from the Tethys penetrated into the epicontinental Germanic sea as well as farther east along the Tethyan northern shore (Dagys, 1993; Palfy, 2003; Stiller, 2001; Sun, 1979). In the Ladinian, Tethyan brachiopods penetrated further into boreal regions (Michalik, 1987). Overall, the majority of Ladinian fauna consisted of Anisian holdovers but some new genera appeared. Compared to the Anisian, brachiopod diversity dropped to approximately 20 genera in the Ladinian (Dagys, 1993). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 83 The Late Triassic brought about an evolutionary explosion within brachiopod associations. In the Camian, brachiopods experienced significant diversification with the most diverse fauna situated on the southwestern Tethys while similar faunas extended to the northwestern Tethys (Dagys, 1993; Gaetani, 1969; Michalik, 1987; Torti and Angiolini, 1997). Extensive Norian regression caused local extinction in nearshore basins, and as a result endemic, opportunistic brachiopod taxa increased (Michalik, 1987). During this stage, typical Mesozoic-Cenozoic taxa appeared with the richest fauna existing in the northwest Tethyan shelf (Dagys, 1993; Golebiowski, 1989). Methods Sample collection and processing The data in this study comprises geological, ecological, and taxonomic information from the 14 regional sites spanning the Middle and Later Triassic (Figure 34). Data was collected from a variety of published, unpublished (i.e., dissertations), and summary data sources. Summary data was utilized from the Paleobiology Database (PBDB), a public, electronic resource for the scientific community. The PBDB is housed at the National Center for Ecological Analysis and Synthesis (NCEAS) and is associated with University of California at Santa Barbara, CA. This NSF funded database is a collaborative data compilation project initiated by Dr. John Alroy, Dr. Charles Marshall, and Dr. Arnold Miller and is extremely unique in that it provides locality-specific faunal inventories including geographic, environmental, and geologic data for each locality (http://paleodb.org). Any published data that was not previously in the PBDB was entered into the PBDB as new collections. Data were compiled into a comprehensive, relative abundance database. Samples within this database are defined as closely spaced horizons from the same regional Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 84 locality, within the similar primary lithologies. Each sample consists of at least 200 specimens. Two taxonomic descriptors were used in subsequent analyses: order and genus. Although different authors originally identified these specimens, museum collections and published photographs were utilized to confirm taxonomic identification. Original abundance counts were transformed into percent specimen per sample (i.e. 1-100%). In total, this study analyzed thirteen Middle Triassic and eleven Late Triassic samples with a total count of 21,671 specimens (Tables 1 and 2). Generally, samples are from a subtropical, carbonate shelf environment. Samples were differentiated into appropriate geological stages, paleogeographic realm and depositional environments within the shelf environment. Specific environments are shown in Figure 14. Although some references included specimens from reefal areas, this data was not incorporated into my analyses. Specimens were categorized into their appropriate taxonomic group, brachiopod or mollusc (mollusc consists of bivalves and gastropods), where they lived in relation to the substrate and their feeding habits. Brachiopods were categorized into two ecological niches: 1) pedunculate suspension feeders; and 2) reclining suspension feeders. Bivalves were categorized into four ecological niches: 1) burrowing deposit feeders; 2) burrowing suspension feeders; 3) cemented suspension feeders; and 4) epibyssate suspension feeders. Gastropods fell into one ecological category: epifaunal grazers. Sampled realms roughly correspond in amounts (Tables 1 and 2). For the Middle Triassic the Germanic epicontinental sea realm equaled 2085 specimens (17%), the Northeastern Tethys realm consisted of 5054 specimens (42%) and the Northwestern Tethys realm comprised 4906 specimens (41%). For the Late Triassic, the Eastern Pacific realm consists of 5427 specimens (-50%) and the Northwest Tethys realm consists of 5409 specimens (-50%). In addition, analyzed facies and sampled stratigraphic intervals are approximately equal except in one stage, the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. TABLE 1: M IDDLE TRIASSIC SAM PLE LOCALITIES, GEOLOGY, AGE, AND ABUNDANCE Locality Sample Code* Lithology Realm Depositional Environm ent Regional Abundance- Stage Trentino, Italy G al Poland K al Poland Ka3 Male Karpaty M tns., Slovakia K ol Balaton Highland, Hungary PI Balaton Highland; Hungary P2 Balaton Highland, Hungary P3 B uizhou, China S 1 uizhou, China S2 Guizhou, China S3 Val Parina, Italy T ol Veszprem, Hungary V2 Veszprem Hungary____________ V3 Lim estone Wavy lim estone Bivalve coquina Lim estone Biodetrital lim estone Limestone Limestone Claystone/wackestone Bioclastic lim estone Bioclastic lim estone Lim estone Dolom itic lim estone Biodetrital lim estone N W Tethys N W Tethys N W Tethys N W Tethys N W Tethys N E Tethys N E Tethys N E Tethys N W Tethys N W Tethys N W Tethys M iddle carbonate shelf A nisian 431 8 uter shelf margin A nisian 1470 uter shelf margin A nisian 615 M iddle carbonate shelf Ladinian 203 Inner carbonate shelf A nisian 786 Shallow interplatform basin A nisian 820 M iddle carbonate shelf A nisian 625 Offshore basin A nisian 4323 O uter shelf margin A nisian 468 O uter shelf margin A nisian 263 Shallow interplatform basin Ladinian 215 M iddle carbonate shelf A nisian 304 Inner carbonate shelf__________ Anisian 312 * Abbreviations: Ga 1 - Gaetani (1969); Ka 1, Ka3 - Kaim (1997); Ko 1 - and M ichalik (1986); P I, P2, P3 - Palfy (2003); S I, S2, S3 - Stiller - Torti and Angiolini (1997); V2, V3 - Voros and Palfy (1989); GES Epicontinental Sea; Fm. - Formation. ■Kochanova (2001); Tol - Germanic oo Ul Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. TABLE 2: LATE TRIASSIC SAM PLE LOCALITIES, GEOLOGY, AGE, AND ABUNDANCE Locality Sample Lithology Realm Depositional Environm ent Regional Abundance Code* Stape Trentino, Italy Trentino, Italy N. Ca careous N. Ca careous N. Ca careous Nye County, Nye C ounty,. Nye County, I r f e W ’ SiIickA Brezos F A ps, Austria < A ps, Austria ( A ps, Austria evac a,U SA evac a, USA evac a, USA ( 'i ji vlarl/limestone NV 3joclastic lim estone N \ <tm estone , NV ijoclastic, wackestone E. ^ime m udstone E. ^lme m udstone, , E. ^lme m udstone/wackestone E. 3 ackstone E. lim estone NV n P a et el el 'el ret C l C l Cl Cl Pet tys S lys N lys S tys I T JC 1 C 1 C 1 C hvs 1 \ tallow interplatform basm C lddle carbohate shelf C lallow interplatfonn basin R imer carbonate shelf, R liddle carbonate shelf R •uter shelf margin C asm C asm b ficfSle carbonate shelf b /fiddle carbonate shelf C am jan 665 am ian 246 laetian 302 laetian 3614 laetian 235 am ian 3581 artuan 692 onan 21? orian 731 onan 205 am ian 347 ........... ♦Abbreviations: F I, F 2 - Fiirsich and W endt (1977); G l, G2, G6 - G olebiowski (1990); H I, H2, H3, H 4 - Hogler (1994); LI - Laws (1982); Si2 - Siblik (1986). oo Os 87 Ladinian. Despite this substantial variation in the Ladinian, this stage comprises 418 specimens, which is a sufficient sample size for reliable statistical results. All other analyzed samples have sufficient sample sizes to allow for reliable quantitative comparisons (Tables 1 and 2). Analytical Methods This study takes a two-stage approach to multivariate analyses. First, an investigative stage searches for patterns independent of the grouping variable; second, the confirmatory stage confirms the statistical significance of patterns seen in stage one. Data matrices are composed of compositional data with samples described by taxonomic or ecological percents. Specimens comprising less than 1% of a sample were deleted to reduce the amount of noise in the datasets and aid in interpreting results. In all analyses, less than 26% of the data was lost as a result of this operation. Since there is a high degree of variation among attributes within samples, the data were log transformed before analyses. This study aims to reveal environmental and/or ecological patterns controlling community patterns, detrended correspondence analysis (DCA) (Hill, 1979) is an appropriate exploratory analysis for these datasets (Gauch, 1982). In addition, DCA minimizes an arch effect and results in superior conclusions compared to other ordination techniques (Gauch, 1982; Hill and Gauch, 1980). The confirmatory analysis chosen for these datasets is multi-response permutation procedure (MRPP). MRPP is a non-parametric procedure for testing the hypothesis of no difference between two or more groups of entities (McCune, 1997). MRPP was chosen because unlike discriminant analysis and multivariate analysis of variance (MANOVA), MRPP does not assume normality, which is seldom met with ecological data (Biondini et al., 1985). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 88 PC-ORD Version 4, software for multivariate statistical analysis of ecological data, performed both exploratory (DCA) and confirmatory (MMRP) analyses. Results Multivariate Taxonomic Analysis Using detrended correspondence analysis (DCA), four data sets were originated from the raw data and analyzed independently: Middle Triassic genera, Middle Triassic orders, Late Triassic genera and Late Triassic orders. The Middle Triassic ordinations indicate that the Germanic Epicontinental Sea, Northeastern Tethys and Northwestern Tethys realms form separate groups with distinct taxonomic composition. However, the separation tends to be better for the genera than the orders (Figure 35). When grouped by depositional environment and stratigraphic age, the samples indicate substantial overlap in each case (Figure 35B, C, E, F). Since DCA analyzes samples and specimens simultaneously, each genus was coded according to their relation to the substrate (i.e., epifaunal or infaunal), ecological category, and specific groups (i.e., brachiopod or mollusc) and plotted their specimen scores in ordinal space. When genera are categorized into substrate relation, infaunal genera plot on the graph periphery (Figure 36A). However, when genera are grouped according to their groups (i.e., brachiopod or mollusc), the genera overlap between groups (Figure 36B). When Middle Triassic ordinations samples scores and specimen scores are presented together, noticeable patterns become apparent (Figure 37). First, samples tend to group near their most abundant genera or order. For example in Figure 37A, PCHIA (i.e., Piarorhynchia sp.) comprises about 50% of sample Gal (See Table 3 for genera codes). Considering this genus only occurs in sample Gal it plots further away from the other samples. The genus MEN (i.e„ Mentzelia sp.) occurs in all samples except P2, K al, and Ka3; as a result, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 89 A X X O G E S * A NE Tethys X NW Tethys 1 0 0 A * X D O G E S * A NE Tethys X NW Tethys o * 0 X 2 0 A X X A B 0 Inner Shelf X Outer Shelf A Middle Shelf A Offshore Basin A £ ] Interplatform Basin A A i X X □ 1 0 X < 1 A O Inner Shelf X Outer Shelf A Middle Shelf A Offshore Basin □ Interplatform Basin □ A x o % X F 0 Anisian A Ladinian % 0 A 0 8 o 0 0 o o c A 0 0 Anisian A Ladinian 8 % 1 o 0 0 o <2> 0 Figure 35: Middle Triassic detrended correspondence analysis of samples. Relative abundance data of genera (A-C) and orders (D-F) are plotted above. A-C display the genus-level ordination plots for samples grouped by (A) paleogeography, (B) depositional environment, and (C) stratigraphic stage. D-F display the order-level ordination plots of samples grouped by (D) paleogeography, (E) depositional environment, and (F) stratigraphic stage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 90 O O O O 8 O Epifaunal A . Infaunal O A B O A O Brachiopod ▲ Mollusc I 8 O o<? o 0 A A o B u rrow ing Suspension P ed u n cu late Suspension E p ifau n al G ra zer E p ibyssate Suspension E pibyssate Suspension P ed u n cu late S u spension □ ▲ Burrowing Suspenison Feeder O Cementing Suspension Feeder □ Epibyssate Suspension Feeder ■ Epifaunal Grazer X Pedunculate Suspension Feeder X > ?< X X O A X Figure 36: M iddle Triassic detrended correspondence analysis of genera. A-C: Ordination of genera grouped by (A) substrate preference, (B) faunal group (i.e., brachiopod and mollusc), and (C) ecological niche. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 91 c-t C/5 ’S < Cru . O Dao Arc Kol O Rux A V2 Ang O Genera A Samples Cas Pchela Euc Lei Ena Pse Kal Coe Dih Ka3 Nud A S3 Qin Men Gal Pchia Axis 1 C/5 < r Athyridida o O Order A Samples PI A P3 P2 A T o l Terebratulida ° Kal ^piriferinida A Kol A Gal Pectinoida A V3 0 Ka3 A A S3 A O Rhynchonellida ^ S 1 aS2 Veneroida x /o Trigonoida O Pteroida O — Archaeogastropoda Axis 1 Figure 37: Middle Triassic detrended correspondence analysis. Samples and taxa are plotted together in ordinal space. (A) ordination patterns of samples and genera. (B) depicts ordination of samples and orders. Sample codes are listed in Table 1 and genera codes are listed in Table 3. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 92 TABLE 3: Group SPECIMEN INFORMATION FOR M IDDLE AND LATE TRIASSIC GENERA Order Genus Genus frebratulida , /ncfioneljida /nchonellida ebratuhda , JiynchonpTIida erebratuhda ynchonejjiqa lynchpnelhda ifritenniga JirjFenmda biriFermida Jhyridida /nchonellida ynchonplhda lerepratulida nriferinjda ^rebratulida , icnonellida yndida Knynchonellida Tefebratulida iDirirerinida sreotaenioglossa 'terioic a Jterioic a Jtenoic a Jterioic a Pterioida . Trigpmojda Pectinoida Arcbaepgastropoda Pterioida Veaeroida Actinps.treon Nuculojda Veneroida Veneroida Arcbaepgastropoda Veneroicja Veneroida Veneroida Archaeogastropoda Ecological alfifi Geological Periods 11 o u s ) IP p u s ) o S u s) m aus ur pus ) rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rac rap o o o o o o o o o o o o o o o o o o o o p. uopoc HO > O C no xx 1)0 )0C 110 )0C no xx no )oc no )oc no joe no )oc 110 IO C no loc no jot no loc no joe no joe no loc no joc 110 IO C no >oc 110 IO C tlio )0 C u se use use use use use use use use use use use use use use use use use use use 11 S C _ _ _ Angustpthyris Xustrirnynchia. < aucasprhynchia -oenQthyrls < ostirhytichopsis $x>lKomynchia MSiSirnyncnia ^eiolepismatina denfzfejia, Nudispirift Dxyccjpellq :iar< jenna lella u a la ^laTornync i barorhync i iLectoconcn ingy.ema laetina hyncbonella refractjnella, „ m gpnirhynchella ceuleria „ Juem axerella . ....pujlina Arcavicula ^aife.vellia ^ ssian ella } ao n ella. ;Iegantim a ;nantiostrepn loscala aia socypnna *Jiaphiston tuxingella jeptocardia O f e n te lla nassic riassic . . t Triassic* e.Triassic ate,Triassic . lqd e Triassic idq p.Triassic ate, riassic . e Triassic e Triassic , p.Triassic ,te riassic . iqd eT riassic idd p.Triassic Late. riassic . vlidd p.Triassic ate „ jiassic ate riassic , Jiqd e Tyiassic lid q P.Triassic ate jiassic a te , jiassic r ate, riassic . vlidd p.Triassic ate jiassic ftte Triassic . ic / L t , jiassic* ic c e , jiassic icc e jiassjc ic c e , jiassic idd P.Triassic ate jiassic ate jiassic ate jiassic a te , jiassic ate jiassic Hat?, riassic . vlidd P.Triassic -a te , riassic . yiiddp Triassic ,a te , jiassic -ate, riassic . vlidd e Triassic ♦Abbreviations: Bur Dep - Burrowing deposit feeders; Bur Susp - Burrowing suspension feeder; Cem Susp - Cementing suspension feeder; Epib Susp - Epibyssate suspension feeder; Epif Graz - Epifaunal grazer; Ped Susp - Pedunculate suspension feeders; M id/Lt Triassic - M iddle and Late Triassic. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 93 the closer the sample plots to MEN the higher the relative abundance. Another noteworthy pattern is that the percentage of infaunal genera within a sample (Table 4) generally increases towards the outskirts of the ordination plot. Late Triassic generic ordinations indicate substantial overlap between samples according to their paleogeography. However, all Northwestern Tethys samples plot on the periphery of the Eastern Pacific samples (Figure 3 8 A). Samples also overlap when coded for depositional environment and geological stages (Figure 38B, 38C). Late Triassic ordinal patterns indicate similar overlapping patterns within paleogeography, depositional environment, and age (Figure 38D, 38E); however, only one Rhaetian sample overlaps into the Norian samples (Figure 38F). When Late Triassic genera are coded according to their taxonomic group, ecology, and substrate preference, the greatest separation is between brachiopods and molluscs (Figure 39B). Although genera tend to overlap according to substrate preference and ecology, fauna reflect similar patterns as depicted in group membership. That is, pedunculate brachiopods separate from the other ecological categories. Figure 40 reveals overall sample patterns in relation to the plotted generic scores. Similar to the Middle Triassic sample/specimen plot (Figure 37), Late Triassic samples plot near the genera that are most abundant in their sample. Specifically, all samples in the bottom left comer (i.e., Si2, H3, G l, and G6) consist of epifaunal brachiopods while most of the other samples contain a mixture of epifaunal and infaunal bivalves. Samples H4 and G2 include both brachiopods and bivalves; H4 sample contains more brachiopods (i.e., 45% of the sample) than sample G2 (i.e., 6% of the sample), thus plotting closer to the samples largely composed of brachiopods (i.e., lower left comer). Likewise, G2 plots near samples dominated by bivalves: HI and H2. Results from the multi-response permutation procedure (MRPP) confirm some ordination patterns but not others. Note the T-statistic; this calculation Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 94 A O East. Pacific A NW Tethys B O Inner Shelf X Outer Shelf A Middle Shelf A Offshore Basin l~l Interplatform Basin A □ < A ° A A A m 0 Carnian C A Norian A X Rhaetian O o O X X A A X D O East. Pacific A NW Tethys O A O % o ► A E O Inner Shelf X Outer Shelf A Middle Shelf A Offshore Basin Q Interplatform Basin X □ 4 a < <i A F O Carnian A Norian X Rhaetian O O o * A o Figure 38: Late Triassic detrended correspondence analysis o f samples. Relative abundance data o f genera (A-C) and orders (D-F) are plotted above. A -C display the genus-level ordination plots for sam ples grouped by (A) paleogeography, (B) depositional environm ent, and (C) stratigraphic stage. D -F display the order- level ordination plots of sam ples grouped by (D) paleogeography, (E) depositional environm ent, and (F) stratigraphic stage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 95 Burrowing Suspension Cementing ' Suspension Epibyssate Suspension O Epifaunal A Infaunal O Brachiopod A Mollusc A Burrowing Suspenison Feeder O Cementing Suspension Feeder □ Epibyssate Suspension Feeder ■ Epifaunal Grazer X Pedunculate Suspension Feeder Figure 39: Late Triassic detrended correspondence analysis of genera. Ordination of genera grouped by (A) substrate preference, (B) faunal group (i.e., brachiopod and mollusc), and (C) ecological niche. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 96 O Genera A Samples Tut £ Cas F2 ( A FI Amp Rhap Ger Pal Ate Bak Iso Sep Si2 N uc. Hal L opO Cau Cos G2 HI H2 G1 G6 H4 Pie Fis Aus Oxy Z u g O ] O Order A Samples Actinostreon Archaeogastropoda Rhynchonellida HI jjj2 Spiriferinida Nuculoidia Neotaenioglossa G1 G6 Veneroida H4 H3 H2 G2 Terebratulida Athyridida Pteroida Figure 40: Late Triassic detrended correspondence analysis. Samples and taxa are plotted together in ordinal space. (A) Ordination patterns of samples and genera and (B) depicts ordination of samples and orders. Sample codes are listed in Table 2 and genera codes are listed in Table 3. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 97 TABLE 4: THE RATIO OF EPIFAUNAL GENERA VERSUS INFAUNAL GENERA (IN PERCENTS) lrachippod:Bivalve:Gastropnrt ■MiirsiniTilLwjsfnKHiiKi ice icc icc icc icc icc icc icc icc I C C icc icc m p . -ate gka] Periods! e , jiassic e , jiassic e , jiassic e jiassic e , jiassic e , jiassic e , jiassic e , jiassic e , jiassic e jiassic e , jiassic e , jiassic riassic riassic a te , jiassic ate jiassic ate jiassic a te , jiassic ate „ jiassic a te , jiassic a te , jiassic -ate, jiassic -ate, jiassic -ate Triassic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 98 TABLE 5: M RPP RESULTS FOR MIDDLE TRIASSIC TAXONOMIC A PRIORI GROUPS Group Comparison T-Statistic* p value G enera >tr.ate (infaunal vs. epifaunal) :moppd vs. MolluscS i Ecology, . „ , 0.01 1001 •racl ihic Stages .nvironment •enositioi Iruers 'eographiq .nvirom *T-statistic describes the distance (or separation) between analyzed groups of samples categorized according to paleogeographic or lithological criteria and groups of genera according to their ecology and taxonomic groups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 99 TABLE 6: M RPP RESULTS FOR LATE TRIASSIC TAXONOMIC A PRIORI GROUPS |^QUj3 Comparison T-Statistic* p value Substrate (infaunal vs. epifaunal) -6.04 Q .Q Q i Bracmopod vs. MolluscS -4.39 0.00 ^ je o g e o e r^ h jq Realms -2!9o Q iO Q : athostrangraphic. Stages -2.79 0.00 JrS e rs'o n a l Environment -0.86 0.19 ’aLeogeographiq Realms -1.27 Q.l 1 ^thostrangrabmc. Stages -2.25 0.03 Jepositioiral Environment________________ Qjgl___________ 0 .6 7 *T-statistic describes the distance (or separation) between analyzed groups of samples categorized according to paleogeographic or lithological criteria and groups of genera according to their ecology and taxonomic groups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 100 describes the separation between groups (Tables 5 and 6). For example, there is a high separation between Middle Triassic taxonomic groups (-10.17) indicating that brachiopods and molluscs are highly distinct and thep-value (p < 0.000) indicates that these groups are significant different. In addition to taxonomic groups, significant Middle Triassic patterns include relation to substrate (infaunal and epifaunal), taxonomic ecological categories, and paleogeographic realms (Table 5). Late Triassic patterns indicate that substrate preference displays the greatest separation, followed by taxonomic membership, ecology, paleogeography and lithographic stages, all of which are significantly different (Table 6). Multivariate Ecological Analysis The percentage of ecological categories per sample were calculated which generated two ecological data sets, a Middle Triassic and Late Triassic data set. Any ecological category with <1% of the total number of specimens was deleted and as a result, the Middle Triassic consists of five and the Late Triassic consists of seven ecological categories (Table 3). The ecological ordination plots result in the overlapping of groups in the Middle and Late Triassic (Figure 41 and 42). In both time intervals, paleogeographic realms provide greater separation between groups. However, overall, the Middle Triassic presents greater separation than the Late Triassic. The ordination plots displaying samples and ecological category simultaneously reveal some interesting patterns (Figure 43 and 44). Both plots generally preserve the sample associations displayed in analyses of genera (Figure 37A and 40A). The Middle Triassic ecologic plot (Figure 41) depicts samples PI, P2, P3, G al, and Tol in the same ordinal space; similarly, in Figure 37A, these samples are plotted near each other. In addition, K al, Ka3 and SI, S2 depart from the left side of the plot similar to the peripheral Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 101 A 0 O G E S * A NE Tethys o X NW Tethys X AX ±A X X B O Anisian A Ladinian * o O o o O Inner Shelf X Outer Shelf A Middle Shelf A Offshore Basin Q Interplatform Basin Inner Shelf Interplatform ' Basin M iddle Shelf Figure 41: M iddle Triassic detrended correspondence analysis of samples described by the relative abundance of ecological categories. A-C displays genera-ecotype ordination plots for samples grouped by (A) paleogeography, (B) stratigraphic stage, and (C) depositional environment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 102 A A oo 0 East. Pacific A NW Tethys ► O ► o f t O Carnian A Norian X Rhaetian 00 Rhaetian Norian □ X A O O Inner Shelf X Outer Shelf A Middle Shelf A Offshore Basin [ ] Interplatform Basin Interplatform A Basin A Middle Shelf I Offshore Basin Figure 42: Late Triassic detrended correspondence analysis of samples described by the relative abundance of ecological categories. A-C displays genera-ecotype ordination plots for samples grouped by (A) paleogeography, (B) stratigraphic stage, and (C) depositional environment. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 103 Cementing _ Suspension O Ecological Category A Sam ples___________ Burrowing Suspension Ka3 _ A O K al A Pedunculate Suspension S3 S1 ^ A Epifaunal Grazers I V3 O G al A PI P2 P3 Tol V2 A q Epibyssate Suspension Figure 43: M iddle Triassic detrended correspondence analysis of samples described by the relative abundance of ecological categories. Ecological categories and samples are plotted together. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 104 Epifaunal O Grazers O Ecological Category A Sam ples___________ FI ▲ Burrowing Deposit Burrowing Suspension o Epibyssate Suspension LI ▲ H I H2 y G2 ▲ Reclining Suspension 1H4 Cementing Suspension F2 Pedunculate Suspension Figure 44: LateTriassic detrended correspondence analysis of samples described by the relative abundance of ecological categories. Ecological categories and samples are plotted together. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 105 placement of K al, Ka3 and SI, S2, S3 (Figure 37A). In comparison to the Middle Triassic ecologic analysis, the Late Triassic samples within the ecologic plot (Figure 44) display a more precise association to their generic counterpart in that the sample ordering is similar (Figure 40A). Figure 44 depicts H I, H2, and G2 grouped together, then H4 plots near the center, and lastly Si2, H3, G1, and G6 plot on the opposite side. MRPP results indicate that the Middle and Late Triassic ecological groups are less distinctive than taxonomic groups and associated p-values are much less significant (Table 7). Discussion Multivariate analysis results indicate that abundance patterns control Middle and Late Triassic sample distributions. That is, samples plot near the taxa that comprise the greatest abundance within that particular sample. But, what is controlling these abundance patterns? To answer this, samples have been coded for their paleogeography, depositional environment, age and taxa have been coded for their substrate preference, taxonomic group, and ecological category. When samples patterns are examined, similar predominant factors control sample distribution within the Middle Triassic and Late Triassic. The Middle Triassic ordination plots indicate that paleogeography largely controls sample distribution (Figure 35). This result is confirmed by the MRPP results (Table 5). Ordination plots of taxonomic patterns do not exhibit clear separation between taxa; instead, large groups of similar categories plot in the center and different categories are pushed out towards the periphery of the plot. For example, you find the only infaunal taxa on the edges of the ordination plot (Figure 36A); Likewise, mollusc taxa plot thinly along the top of Figure 36B and lastly, in Figure Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 106 TABLE 7: M RPP RESULTS FOR M IDDLE AND LATE TRIASSIC ECOLOGICAL A PRIORI GROUPS - T-Statistic* p value -0.29 0.35 je s 1.02 0.86 epositioriai Environm ent 0.66 0.50 .ate Triassic Paleogeographic Realms -0.97 0.15 Lithostrau graphic. Stages -1.07 0.14 DepQSitionalEnvirQnment________________ (L25___________ 0-54 *T-statistic describes the distance (or separation) between analyzed groups of samples categorized according to paleogeographic or lithological criteria. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 107 36C, pedunculates generally plot in the center, while burrowing suspension feeders are at the extreme ends of the plot, as are most mollusc ecological categories. These peripheral patterns are mentioned because based on the MRPP results it is reasonable to conclude that these patterns are meaningful. MRPP results reveal that the greatest separation lies between brachiopod and mollusc taxa, followed by substrate preference and ecological niches (Table 5). Thus, although there is visible overlap between taxa, taxa that plot on the periphery are significant different then those that plot in the center. Therefore, it is concluded that taxonomic differentiation between brachiopod and molluscs affect Middle Triassic faunal patterns greatly followed by the ecology of the taxa. Paleogeography possess the least influence on faunal patterns. Although there are differences among paleogeographical realms, an increase in homogeneity between samples could occur due to the extensive prograding transgression into coastal regions that was occurring during the Anisian (Embry, 1988; Michalik, 1987). Therefore this increase of homogeneity could have lessened the overall influence paleogeography had on faunal patterns. This homogeneity is exhibited by the similar occurrences of Northeastern Tethys realm genera in the Northwestern Tethys realm (MEN - Mentzelia and ANG - Angustothyris). Likewise, genera from the Northwestern Tethys realm occur in the Germanic Epicontinental Sea (e.g., COE - Coenothyris). In sum, group membership (brachiopod or mollusc), ecologic habits, and paleogeographic reference control Middle Triassic faunal patterns. Therefore, at this scale of study, onshore-offshore environments and geological time, both usually perceived as important factors, play secondary roles in the multivariate position of Middle Triassic samples. Late Triassic sample ordination plots reveal similar peripheral patterns as the Middle Triassic. Here, although paleogeographic realms overlap, the Eastern Pacific Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 108 realm samples plot in the center and the Northwest Tethys plot toward the edges (Figure 38A). MRPP results indicate that the differences between these two realms differ significantly (Table 6); thus implying that genera tend to be more restricted to particular localities. These results are not surprising since a continent separates the two realms (Figure 33). Increased endemism is also supported by records of increased differentiation between brachiopod faunas due to extensive regression at the Norian/Rhaetian boundary as well as the documentation of the first appearances of typical Mesozoic-Cenozoic brachiopod genera (Dagys, 1993; Golebiowski, 1989; Michalik, 1987). Although the sample ordination plots do not indicate difference among lithological stages (Figure 38C), MRPP results indicate significant difference between stages (Table 6). These out of phase results can be explained by looking at where the data comes from. Since all the Norian data was obtained from the Eastern Pacific realm (-11% of Late Triassic data) and the all Rhaetian data was obtained from the Northwestern Tethys Realm (-42% of the Late Triassic data), the significant difference resulting from the MRPP analysis most likely record differences in paleogeography rather than a true difference in age. Taxonomic ordination plots indicate a distinct separation between group membership. A clear line can be drawn between brachiopod and mollusc genera (Figure 39). MRPP results confirm this distinction. Although MRPP results indicate significant differences between substrate preferences, the ordination plot (Figure 39A) depicts some overlap between epifaunal and infaunal taxa. In fact, MRPP results indicate that the difference between these two groups is greater than any other Late Triassic comparison (Table 6). Ecological categories also overlap in the ordination plot but are significantly different according to the MRPP results. In sum, paleogeography and substrate preference, taxonomic membership, and ecological niches influence Late Triassic faunal patterns. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 109 In addition, but to a lesser extent, paleogeographic location affects faunal distribution. Interestingly in both time periods, generic patterns indicate more separation compared to ordinal patterns, thereby indicating that a slight decrease in taxonomic resolution drastically reduces the amount of information preserved within the faunal patterns. Conclusions Intuitively, depositional environment and geologic age are thought to control faunal patterns. An analysis of continuous carbonate shelf environments spanning through the Middle and Late Triassic indicates ecology is the main factor controlling faunal distributions. Together, group membership (brachiopod or mollusc), substrate preference (epifaunal versus infaunal) and ecological niche control faunal distributional patterns. In addition, paleogeographic location influences faunal distributions however, to a lesser extent than ecology. These results demonstrate that the ecology of the constituent taxa is extremely important to faunal distributional pattern during this time. In addition, provenance becomes important to faunal pattern differentiation during regressive intervals when direct marine connections between realms are lacking. The relatively poor discrimination of faunal assemblages across depositional environments and lithostratigraphic stages reflects the overriding role ecology and, to a lesser extent, paleogeography, plays in the structure of the Middle and Late Triassic faunal associations. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 110 Chapter 4: Late Paleozoic Brachiopod and Bivalve Patterns: A Quantitative Study of Faunal Patterns within the Late Carboniferous and Early Paleozoic Abstract Brachiopod and bivalve dominated fossil assemblages from the marine Late Carboniferous and Early Permian of North and South America, Thailand and Australia were analyzed. Using bulk samples, this study explores quantitative patterns recorded by the marine benthos including implications for paleogeography, depositional environment (along an onshore-offshore gradient), stratigraphic position, taxonomic groups (brachiopod or mollusc), substrate preferences, and ecological niches. A total of 336,321 genera were pooled from primary and summary literature resources. A total of 29 samples were analyzed from carbonate platform environments within Nevada, Kansas, Oklahoma, Texas, Utah, New Mexico, Venezuela, Kanchanaburi (Thailand) and Queensland (Australia). Samples were categorized into paleogeographic location, depositional environment, and age. All specimens were identified to the genus-level and classified in terms of their taxonomic membership, substrate preference, and ecological niche. Categorization was completed in order to help differentiate the factors controlling faunal patterns Relative abundance data were analyzed using detrended correspondence analysis (DCA) and multi-response permutation procedure cross-validated the a priori categories (i.e., paleogeography, depositional environment, stratigraphic position, and specimen ecology). Multivariate analyses indicate that pedunculate and reclining suspension feeders (i.e., brachiopods) and endobyssate, epibyssate, cementing suspension feeders (i.e., bivalves) cluster together. In contrast, burrowing suspension and deposit feeders (i.e., bivalves) along with epifaunal grazers (i.e., gastropods) cluster together separate from the later brachiopod-bivalve groups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ill This concludes that brachiopod associations are not segregated according to the taxonomic distinction between brachiopods and bivalves. Instead, within this study, ecological distinction separates brachiopod associations based on the substrate preferences of the particular genera, which is infaunal versus epifaunal. Introduction This paper documents the paleoecological patterns of brachiopod and molluscan genera from 10 locations spanning the Pennsylvanian through the Early Permian. Paleoecological analysis, an analysis that incorporates ecological and geological faunal information, aids in understanding clade changes through time. In the history of marine invertebrate faunas a marked switch between Paleozoic brachiopod dominated faunas and bivalve dominated Modem faunas took place. It is now clear that mass extinction affects these two clades (Gould and Calloway, 1980); however, the exact cause of the decline of brachiopod communities has not been explained. This paper is part of a series of papers aimed at documenting brachiopod communities before and after the Permian-Triassic mass extinction. The goal of this paper is to gain a better understanding about the general mechanisms controlling Paleozoic brachiopod communities. Once the Paleozoic brachiopod communities are analyzed, the results will be compared to a similar analysis of Mesozoic brachiopod communities. Previous studies document paleoecological patterns during this time period (Hoover, 1981; Olszewski, 2001; West, 1970; Yancey and Stevens, 1981). However, this study combines their data along with other taxonomic studies in order to gain a larger perspective on brachiopod community patterns during this time interval. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 112 Study Area and Geological Setting This study focuses on three marine realms that existed along Pangea throughout the Pennsylvanian to Early Permian: the Northwestern Continental Margin, the Northwestern Midcontinent, and the Southeast Boreal (Figure 45 and 46). All realms consist of mixed siliclastic and carbonate sedimentary sequences. Data sampling concentrated on the late Carboniferous, Moscovian and Gzhelian stages and the Early Permian Asselian, Sakmarian, and Artinskian stages (Figure 46). Data were analyzed from these stages according to their period divisions, that is, late Carboniferous and Early Permian groups (Figure 46). All environments record relatively shallow marine settings within subtropical and boreal regions. There is abundant evidence suggesting that the early part of the Carboniferous was generally warm. However, through time, pronounced cooling occurred resulting in a Gondwanan ice sheet covering the southpole by the Late Carboniferous period (Crowley and Baum, 1991; Ziegler et al., 1997). As the Permian began, glaciers continued to cover much of Gondwanaland, as they had during the late Carboniferous. At the same time the tropics were covered in swampy forests. In general, while climate waxed and waned, depositional cyclothems, characteristic of the Pennsylvanian and Permian Periods, were deposited in the Northwestern Midcontinent. Cyclothems typically contain a sequence of rock layers that indicate a progressive change in depositional environments from coal swamp, to marine, to non-marine, and back to coal swamp and appear to be generated by interaction of tectonic subsidence, sedimentation, and eustacy (Bennington, 2002). More detailed geological information will be presented in the following paragraphs according to their specific realms. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 113 A Late Carboniferous - 300 Ma N o i'lln u s U m Continental Margin Northwestern Mideonlinenl B Harly Permian - 2 8 0 iVla INorthss cslern Continental M argin N orthw estern Miileonlinent Southeastern Unreal Figure 45: Late Carboniferous and Early Permian paleogeography. (A) Late Camboniferous samples; Location A, the Northwestern Continental Margin, combines data from Beus and Lane (1969); Location B, the Northwestern Midcontinent, combines data from Mudge and Yochelson (1962); 01szewski(2000); and West (1970) (B) Early Permian samples; Location C, the Northwestern Continental Margin, combines data from Yancey and Stevens (1981); Location D comprises data from Kues (1995) and E comprise data from Cooper and Grant (1972), Hoover (1981), and Mudge and Yochelson (1962), both of which are in the Northwestern Midconintent realm. Location F comprises data from Grant (1976) and Waterhouse (1983) and G comprises data from Waterhouse (1983) both of which are within the Southeast Boreal realm. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 114 Stratigraphic position of Geochronology samples according to paleogeographic realm "8 •c NW NW SE C d 5 8 cu 0 0 Cont. Mid- Boreal O - cl- uj 3 c /5 Margin Cont. 256 Kungurian 260 c ed C cd Yal C ol Wa3 < L > O h c 03 C O Ya2 G rl H oi 0 3 ■ f l Ya3 Gr2 269 u . tS 3 C O u < Ya4 Gr3 Gr5 Sakmarian Ku2 282 Asselian M ul Mu4 Mu2 290 c cd 13 JS N Mu5 Mu6 M u 7 n n M„8 oil 297 C O = 3 O u . iP J + -H '£ o o 013 s cd '> O e 303 u* cd u c .2 cd < D .3 c 03 > C O C C & C l , Moscovian B el W ei We2 We3 014 311 c ed •c 3 j a t/3 ed 323 O Q Figure 46: Geochronology from Late Carboniferous through the Early Permian (after Gradstein et al. 2004). International Commission on Stratigraphy (ICS) stage names are used. Samples are categorized according to their appropriate stage and paleogeographic realm. Samples within stages are not arranged in stratigraphic order. *GES - Germanic Epicontinental Sea Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 115 Northwestern Continental Margin Realm Two studies document this realm, from the late Carboniferous (Beus and Lane, 1969) and the Early Permian (Yancey and Stevens, 1981) (Table 8 and 9). During the Moscovian through Artinskian stages, sedimentary deposition within Nevada and Utah occurred near the outer edge of the continental shelf (Stevens, 1977; Yancey and Stevens, 1981). A long-lived, shallow, interior seaway occupied this area adjacent to a deep-marine trough along the western edge of the seaway (Yancey and Stevens, 1981). It should be noted that all faunal information extracted for analyses are only obtained from the interior seaway environment. Northwestern Midcontinent Realm Most of the data used in this study fall within this particular realm (Cooper and Grant, 1972-1977; Hoover, 1981; Kues, 1995; Mudge and Yochelson, 1962; Olszewski, 2000; West, 1970). Because of the vast concentration and detailed study of this particular area, the Northwestern Midcontinent provides comparative material that represents a standard for both faunal comparison and stratigraphic correlation within the Pennsylvanian and Early Permian (Hoover, 1981). Within this realm, Mudge and Yochelson (1962), West (1970) and Olszewski (2000) contributed to the late Carboniferous data and Early Permian data is from the following sources: Cooper and Grant (1972), Hoover (1981), Kues (1995), and Mudge and Yochelson (1962) (See Table 8 and 9). It is generally agreed that late Paleozoic marine sediments in the Western Hemisphere were deposited in a geosynclinal basin or series of basins (Hoover, 1981). Paleomagnetic research places the southern tip of Mexico near the west coast of South America (Hoover, 1981; Ziegler et al., 1997) (Figure 45). This connection produced a more intimate pre-Mesozoic connection between the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. Locality TABLE 8: LATE CARBONIFEROUS SAM PLE LOCALITIES, GEOLOGY, AGE, AND A BUNDANCE Sample Prim ary Lithology Realm* Depositional Environment Regional _SL Abundance Nevada, USA Cansas, f Cansas, i Cansas,1 Cansas, 1 Cansas, Cansas, 1 .vansas, 1 ____ Kansas! USA aiom a, a loma, : a lo m a ,1 ; a loma, lahoma, Packstone .jir^estone .jn^estone .jmestone kstone illaceous wackestone e e e e £_ NW Contm ental M argin fort w estern ] w e s te r n , w e s te rn : w estern w estern w estern w estern 1 ic continent K continent K continent ic continent ic continent ic continent ldcontinent w estern M jdcontjnent w estern Mic continent w estern Ml< continent ort w estern w estern orthwestem lie continent lie continent lidcontinent liddle carbonate shelf iasm 3asin 3asin 3asin 3asm Ja sm M iddle carbonate shelf nner carbonate shelf 3 as in 3asin 3asin iasin 3asm loscovian ian tan ian ian ian ian ian M oscovjan * loscovian loscovian loscovian loscovian loscovian ♦Abbreviations: B el - Beus and Lane (1969); M u5, Mu6, Mu7, Mu8 - M udge and Yochelson (1962); O il, 012, 013, 014 - Olszewski (2000); W ei, We2, We3, We4, We5 - West (1970); N W - N orthwestern O N Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission. TABLE 9: EARLY PERM IAN SAM PLE LOCALITIES, GEOLOGY, AGE, A N D A BUNDANCE Locality Sample Primary Lithology Realm* Depositional nvironm ent , USA . lana lana suri, tana ansas, ansas, ueer evac iasin jim Regional Abundance Stage. Artins A rt ins Artins Artins Artins Artins Yackestone Vreillaceous Lunestone lim estone lim estone mestone vackestone , gillaceous shale lestone Il2llc silts tone sandstone lim estone , , ,aIcareous shale , llaceous W ackestone arckestone fort sout w estern leastem out leastem sout Sout leastem leastem ort w e s te r n ... >ortiw estem v > ort w estern y ■Jort w estern y t w e ste rn , y eastern Boreal Vlidcontinent orea orea orea orea K continent K continent K continent ic continent ldcpntinent ,ontinenta ,ont|nenta .ontinenta nntinenta er carbonate shelf iqqie carbonate shelf ...lqdle carbonate shelf iasin nner carbqnate sh e lf,, Middle carbonate shelf .asm lasm , , nner carbqnate shelf Middle carbonate sh nner car nner car nner car sonate s jonate s son ate s ;lf cian cian cian cian cian kian akm anan A sse Asse, Ass.e A rtinskian A rtinskian Artinskian A rtinskian A rtinskian ♦Abbreviations: C o l - Cooper and Grant (1972); Gr2, Gr3, Gr5 - Mudge and Yochelson (1962); Wa3 - Waterhouse (1983); Y al, - G rant (1976); H oi - H oover (1981); Ku2 - Kues (1995); M u l, M u2, Mu4 Ya2, Ys3, Y a4- Yancey and Stevens (1981); N W - Northwestern 118 southern Appalachian, Ouachita, Mexicana-Central American and northern Andean geosynclinal belts, which in turn helps to explain the faunal similarity between North and South American counterparts (Hoover, 1981). During this time, both North and South American areas represented a broad, flat marine platform adjacent to the Anadarko Basin, a starved foreland basin associated with the Wichita thrust belt (Hoover, 1981; Rascoe and Adler, 1983). Southeastern Boreal Realm Grant (1976) and Waterhouse (1983) compiled taxonomic and geologic information, including faunal counts, from the Early Permian of Thailand and Australia-New Zealand areas. Compared to the broad, extensive platforms of the Western Hemisphere, the Southeastern Boreal realm represented a similar shelf environment but this realm is from a significantly cooler water environment. Studies indicate that although some paleotropical brachiopod genera comprise these faunas, temperate to cool water genera dominate the assemblages (Waterhouse, 1983). In addition, the preservation of pebbly mudstones that resemble diamictites of glacial origin indicates that the regional climate was much cooler compared to the Northwestern Midcontinent and the Northwestern Continental Margin realms (Waterhouse, 1982). Methods Sample collection and processing The data in this study comprise geological, ecological, and taxonomic information from 10 localities spanning the late Carboniferous and Early Permian (Figure 46). Data were collected primarily from the Paleobiology Database (PBDB), a public, electronic resource that provides global, collection-based occurrence Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 119 and taxonomic data for marine animals of any geological age (http://paleodb.org). Most of this data came from peer-viewed publication however, I utilized two PhD. dissertations for further background information (Olszewski, 2000; West, 1970). Data were compiled into a comprehensive, relative abundance database. Samples within this database are defined as closely spaced horizons from the same regional locality, within the same depositional environment. Since samples represent different amounts of time averaging, faunal associations are not considered to represent co occurrence during life. Instead, these samples represent a long history of information regarding fossil associations and assist in the explanation of faunal compositional differences between different realms and environments. Each sample consists of at least 200 specimens. Two taxonomic descriptors were used in subsequent analyses: order and genus. Although different authors originally identified these specimens, museum collections and published photographs were utilized to confirm taxonomic identification. Original abundance counts were transformed into percent specimen per sample (i.e. 1-100%). In total, this study analyzed fourteen late Carboniferous and fifteen Early Permian samples with a total count of 366,321 specimens (Figure 46). Generally, samples are from two environments: a subtropical, eperic sea and a cool water carbonate platform. Samples were differentiated into appropriate geological stages, paleogeographic realm (see definitions above) and depositional environments within the shelf environment. Specific platform categories are shown in Figure 14. In regards to the specimens, they were categorized into their appropriate group (i.e. brachiopod or mollusc), where they lived in relation to the substrate and their feeding habits. Brachiopods were categorized into two ecological niches: 1) pedunculate suspension feeders; and 2) reclining suspension feeders. Bivalves were Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 120 categorized into five ecological niches: 1) burrowing deposit feeders; 2) burrowing suspension feeders; 3) cemented suspension feeders; 4) endobyssate suspension feeders; and 5) epibyssate suspension feeders. Gastropods fell into one ecological category: epifaunal grazers. Sampled realms are extremely variable in abundance within the late Carboniferous; however, within the Early Permian they roughly correspond in amounts (Table 8 and 9). For the late Carboniferous, the Northwestern Midcontinent realm equaled 313,702 specimens (~99%), the Northwestern Continental Margin realm consisted of 237 specimens (~1%) and the Southeastern Boreal realm comprised 0 specimens. For the Early Permian, the Northwestern Midcontinent realm consists of 9,316 specimens (18%), and the Northwestern Continental Margin realm consists of 23,214 specimens (44%), and the Southeastern Boreal realm comprised 19,852 specimens (38%). In addition, analyzed facies and sampled stratigraphic intervals are variable. For example, in the late Carboniferous, the Moscovian stage comprises 96% and the Gzhelian 4% while the deep, muddy offshore environments comprise 99% of this time interval. In the Early Permian, the Artinskian stage comprises 91%, the Asselian 6% and the Sakmarian 3%. Depositional environments break down to approximately 54% shallow, inner shelf; 28% middle shelf; and 18% deep, offshore basin. Despite this substantial variation between particular categories, all comparison categories total to abundances greater than 237, which is a sufficient sample size for reliable quantitative comparisons (Table 8 and 9). Analytical Methods This study takes a two-stage approach to multivariate analyses. First, an investigative stage searches for patterns independent of the grouping variable; Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 121 second, the confirmatory stage confirms the statistical significance of patterns seen in stage one. Data matrices are composed of compositional data with samples described by taxonomic or ecological percents. Since sample abundances vary greatly, as noted above, relative percentages were calculated per sample; otherwise, an extremely abundant sample would bias statistical analyses strongly (e.g.: comparing the late Carboniferous sample Bel, 237 specimens, to sample We 2, 126,596). Specimens comprising less than 1% of a sample were deleted to reduce the amount of noise in the datasets and aid in interpreting results. In all analyses, less than 24% of the data was lost as a result of this operation. Since there is a high degree of variation among specimens within samples, the data were log transformed before analyses. Since this study aims to reveal environmental gradients controlling community patterns, detrended correspondence analysis (DCA) (Hill, 1979) is an appropriate exploratory analysis for several reasons (Gauch, 1982). First, DCA ordinates both specimens and samples in the same multivariate space, which allows a direct assessment of specimens versus samples relations. Second, DCA minimizes an arch effect and results in superior conclusions compared to other ordination techniques (Gauch, 1982; Hill and Gauch, 1980). The confirmatory analysis chosen for these datasets is the multi-response permutation procedure (MRPP). MRPP is a non-parametric procedure for testing the hypothesis of no difference between two or more groups of entities (McCune, 1997). MRPP was chosen because unlike discriminant analysis and multivariate analysis of variance (MANOVA), MRPP does not assume normality, which is seldom met with ecological data (Biondini et al., 1985). PC-ORD Version 4 software for multivariate statistical analysis of ecological data, preformed both exploratory (DCA) and confirmatory (MMRP) analyses. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 122 Results Multivariate Taxonomic Analysis Using detrended correspondence analysis (DCA), four data sets were analyzed, originated from the raw data, independently: late Carboniferous genera, late Carboniferous orders, Early Permian genera and Early Permian orders. The late Carboniferous ordinations indicate that the Northwestern Midcontinent and the Northwestern Continental Margin realms form separate groups with distinct taxonomic composition. However, the separation tends to be better for the genera than the orders (Figure 47). When grouped by depositional environment the samples indicate overlap in each case (Figure 47B, E). However, when grouped by stage intervals, there is a distinction between Gzhelian and Moscovian faunas (Figure 47C, F). Since DCA analyzes samples and specimens simultaneously, each genus was coded according to its relation to the substrate (i.e, epifaunal or infaunal), ecological category, and specific groups (i.e., brachiopod or mollusc) and plotted their specimen scores in ordinal space. When genera are grouped according to their taxonomic groups (i.e., brachiopod or mollusc), the genera overlap between groups but the trend of each group is different (Figure 48B). Molluscs tend to vary along Axis 1 and brachiopods tend to vary along Axis 2. When genera are categorized into substrate relation, infaunal genera plot along the outer limits of the epifaunal cloud of points (Figure 48A). Generic patterns of ecological categories indicate two relatively separate groups. The left side of the plot contains the majority of pedunculate and reclining suspension feeding specimens with a few specimens lingering towards the right (i.e., Cru - Crurithris which is present in all samples, Cle - Cleiothyidina, and Mes - Mesolobus) (Figure 48C). Also, epibyssate, endobyssate, and cementing suspension feeding specimens exclusively plot on the left side. The right side of the plot contains all burrowing deposit feeders with the majority of Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 123 > o O NW Contin. Margin A NW Midcontin. 1 BA O Offshore Basin A Middle Shelf X Inner Shelf 0 P ° % f i P X O Gzhelian A Moscovian 2 P ° e P o D 0 NW Contin. Margin A NW Midcontin. i t A i t c * E O Offshore Basin A Middle Shelf X Inner Shelf 0 0© & O Gzhelian A Moscovian JP Figure 47: Late Carboniferous detrended correspondence analysis of samples. Relative abundance data o f genera (A-C) and orders (D-F) are plotted above. A-C display the genus-level ordination plots for samples grouped by (A) paleogeography, (B) depositional environment, and (C) stratigraphic stage. D-F display the order-level ordination plots of samples grouped by (D) paleogeography, (E) depositional environment, and (F) stratigraphic stage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 124 oQ O A > °o O Epifaunal A. Infaunal o q . Oq O Brachiopod ▲ Mollusc 0 X<^ o & X ‘ " I A Burrowing Deposit Feeder ▲ Burrowing Suspenison Feeder O Cem enting Suspension Feeder • Endobyssate Suspension Feeder □ Epibyssate Suspension Feeder ■ Epifaunal Grazer X Pedunculate Suspension Feeder Reclining Suspension Feeder Figure 48: Late Carboniferous detrended correspondence analysis of genera. Ordination of genera grouped by (A) substrate preference, (B) faunal group (i.e., brachiopod and mollusc), and (C) ecological niche. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 125 epifaunal grazers, while burrowing suspension feeders occur sparingly along Axis 1 (Figure 48C). When late Carboniferous ordination sample scores and specimen scores are presented together, noticeable patterns become apparent (Figure 49). First, as mentioned previously, brachiopods vary along Axis 2 and it seems that the gradient along axis 2 represents a change from pedunculate brachiopods near the bottom left of the plot to reclining faunal associations as you move up along Axis 2. Likewise, along Axis 1, bivalve specimens tend toward higher abundances of infaunal specimens from left to right (Figure 49). Early Permian generic and ordinal ordinations general overlap in all cases, however generic analyses produce less overlap (Figure 50). The least amount of overlap occurs in Figure 50A; only one Northwestern Continental Margin sample overlaps into the Mid-Continental realm (Figure 50A). In comparison, depositional environments and stratigraphic stages overlap significantly between samples (Figure 50B, C). When Early Permian genera are coded according to their taxonomic group, ecology, and substrate preference, although some specimens overlap, the greatest separation is between brachiopods and molluscs (Figure 5IB). Taxonomic groups indicate that the majority of bivalves separate from brachiopods and only overlap at groupings edges (Figure 5 IB). As in the late Carboniferous, bivalve gradients vary along Axis 1 and brachiopods vary along Axis 2. Also similar to the late Carboniferous, genera with certain ecologies tend to separate from one another. For example, burrowing deposit feeders exclusively plot on the left side of the graph with the majority of epifaunal grazers (Figure 51C). Conversely, pedunculate and reclining suspension feeders plot on the right side of the graph with endobyssate and cementing suspension feeders. It is interesting to note that these distinctions among ecological associations are similar to late Carboniferous associations, however, Early Permian genera tend to separate more cleanly (Figure 48C and 51C). The Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 126 Fim Chor K ozPhr Kut Spi Cal Bux Edm Pro Nat O R hi Can 0 ° 0 0 rb Bel > V C ho PhyO % ^ l_ M a r K n io O — P0* 1 - Sep Lino Cle O Sch O We4 We5 Meek Ant W ei We2 We3 O Hys Wil O Samples A Genera B Craniida O Pholadomyoida Athyridia Rhynchonellida Orthotetida O _ ^ ^ P terio d id a-------------- 012 Mu5 013 Productida We4 j B el 014 Orthida O Acrotretida O M ytiloida® W ei Bellerophontida Spirifenda Archaeogasatropoda Schaphopoda Nuculoida Murchisoniina Lingulida O Order A Samples Figure 49: Late Carboniferous detrended correspondence analysis. Samples and taxa are plotted together in ordinal space. (A) ordination patterns of samples and genera. (B) depicts ordination of samples and orders. Sample codes are listed in Table 8 and genera codes are listed in Table 12 . Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 127 > X 0 NW Contin. Margin y A NW Midcontin. X SE Boreal X X 0° X o ik> k A 0 B X* X X O Offshore Basin A Middle Shelf X Inner Shelf o O Artinskian A Asselian X Sakmarian x * D 0 NW Contin. Margin A NW Midcontin. X SE Boreal A A O O O X A o E 0 Offshore Basin A Middle Shelf X Inner Shelf A O C P •^C c < X X X A X X F 0 Artinskian A Asselian X Sakmarian ▲ Figure 50: Early Permian detrended correspondence analysis of samples. Relative abundance data of genera (A-C) and orders (D-F) are plotted above. A-C display the genus-level ordination plots for samples grouped by (A) paleogeography, (B) depositional environment, and (C) stratigraphic stage. D-F display the order-level ordination plots of samples grouped by (D) paleogeography, (E) depositional environment, and (F) stratigraphic stage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 128 I * o o A O Epifaunal A Infaunal O o 0 ® ® o A O A B A A A O Brachiopod A Mollusc o ® O o V A l o x A Burrowing Deposit Feeder A Burrowing Suspenison Feeder O Cementing Suspension Feeder # Endobyssate Suspension Feeder □ Epibyssate Suspension Feeder ■ Epifaunal Grazer X Pedunculate Suspension Feeder ^ Reclining Suspension Feeder Figure 51: Early Permian detrended correspondence analysis of genera. Ordination of genera grouped by (A) substrate preference, (B) faunal group (i.e., brachiopod and mollusc), and (C) ecological niche. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 129 rest of the ecological categories seem to continue along the first axis (i.e. burrowing and epibyssate suspension feeders). Figure 52 reveals overall sample patterns in relation to the plotted generic scores. Three distinct groups of data separate out on this plot. First, samples Wa3 and Gr2, at the top of the plot, contain genera that no other samples share therefore, leading to their separation from the bottom half samples (Figure 52). Second, samples Ya2, Ya3, and Ya4 plot near the left side completely distinct from other groups. The rest of the data plots in the right bottom comer (Figure 52). Results from the multi-response permutation procedure (MRPP) confirm some ordination patterns but not others. Note the T-statistic; this calculation describes the separation between groups (Table 10 and 11). For example, in the Late Carboniferous, the only meaningful categories are taxonomic groups (-21.32) indicating that brachiopods and molluscs are highly distinct and the p-value ip < 0.00001) indicates that these groups are significantly different. In addition to taxonomic groups, significant late Carboniferous patterns include taxonomic ecological categories and lithologic stages for genera and orders (Table 10). For Early Permian patterns, substrate preference displays the greatest separation, followed by taxonomic groups, taxonomic ecology, generic lithostratigraphic stage intervals and order depositional environments, all of which are significant (Table 11). Some groupings are listed as “N/A” within Table 10 because sample sizes were too small to be confirmed. Multivariate Ecological Analysis Percentages of ecological categories were calculated per sample and two ecological data sets were generated, a late Carboniferous and Early Permian data set. I deleted any ecological category with <1% of the total number of specimens and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 130 Gly Tom Calc Terr War p|a Bak piat Gon poi Lepm Sch MeekYun Nucl Euph Ya3^ O Anom O Genera A Samples Bel O Dip Not Ort Spir Grl Mar A Stri O G r5 DemS^, i,^ Chot Uru Comq Crur Avip Euo A co Die Amph Jur Ane Neos B Acrotretida O O Order A Samples P roductida Orthotetida \ \ Gr2 1 Gr3 Grl a ' n 's £ 1 < Gr5 n T O / t “ \M u 2 Orthida / \ / Col Hoi .Veneroida Scaphopod Pholadomyoida JPterioida *-M ul ° Archaeogastropoda OSpiriferida ya4 O t Yal Wa3 ▲ A Ya2 r Murchisoniina K u 2 Terebratulida Spiriferinida Ya3 I Bellerophontida ^ ONiic O O Euomphalina K hynchonellida Trigonioida I Mytiloida O Figure 52: Early Permian detrended correspondence analysis. Samples and taxa are plotted together in ordinal space. (A) ordination patterns of samples and genera; (B) depicts ordination of samples and orders. Sample codes are listed in Table 9 and genera codes are listed in Table 13. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 131 TABLE 10: M RPP RESULTS FOR LATE CARBONIFEROUS TAXONOMIC A PRIORI GROUPS Group Comparison T-Statistic* p value G enera Substrate (mfaunal vs. epifaunal) Bracm oppa vs. MolluscS ,[axa E cology,. „ , ’aleogeographiQ Realms ^lthoslratigraphiQ Stages Jepositional Environm ent ’aleogeographiq Realms Jthostratigraphic. Stages Depositional Environm ent______ *T-statistic describes the distance (or separation) between analyzed groups of samples categorized according to paleogeographic or Iithological criteria and groups of genera according to their ecology and taxonomic groups. t Sample size was s 2 therefore group com parison could not be confirmed. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 132 TABLE 11: M RPP RESULTS FOR EARLY PERMIAN TAXONOMIC A PRIORI GROUPS Group Comparison T-Statistic* p value G enera Substrate (mfaunal vs. epifaunal) Bracmopod vs. Mollusc^ ,[axa Ecology, . „ , ’aleogeographiq Realms athostrangraphiQ Stages J r S e rs '0 Environm ent ’aleogeographjq Realms athostrangraphiQ Stages Depositional Environment______ *T-statistic describes the distance (or separation) between analyzed groups o f samples categorized according to paleogeographic or lithological criteria and groups o f genera according to their ecology and taxonomic groups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 133 as a result, the late Carboniferous and the Early Permian consist of eight ecological categories (Tables 12 and 13). The ecological ordination plots result in substantial overlap of groups in the late Carboniferous and Early Permian (Figure 53 and 54). Although Early Permian ecological ordinations overlap, in comparison to the Late Carboniferous, the Early Permian displays greater separation (Figure 54). For example, the ecology of the Southeastern Boreal realm is similar to the Northwestern Midcontinent realm and only one sample from the Northwestern Continental Margin realm overlaps with the Northwestern Midcontinent (Figure 54A). Differences between the ecology within depositional environment patterns provide the similar overlap and separation (Figure 54B). Lastly, ecological patterns according to stage interval indicate significant overlap between samples (Figure 54C). The ordination plots displaying samples and ecological category simultaneously reveal some interesting patterns (Figure 48 and 49). A gap in the Late Carboniferous plot separates samples into two groups: samples abundant in epifaunal specimens on the left and samples abundant in burrowing and grazer specimens on the right (Figure 55). In contrast, Early Permian samples are less distinct (Figure 56). MRPP results indicate that in the late Carboniferous stage intervals affect ecological patterns within samples (Table 14). In contrast, depositional environments affect Early Permian ecological patterns. As noted in the taxonomic results above, late Carboniferous paleogeographic realms and depositional environments cannot be compared using this technique because more than one sample per category is needed to complete the calculation. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. A 0 NW Contin. Margin A NW Midcontin. A Q* Fk % B O Offshore Basin A M iddle Shelf X Inner Shelf O Gzhelian A M oscovian Figure 53: Late Carboniferous detrended correspondence analysis of samples described by the relative abundance of ecological categories. A-C displays genera- ecotype ordination plots for samples grouped by (A) paleogeography, (B) depositional environm ent, and (C) stratigraphic stage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 135 A O NW Contin. Margin A NW Midcontin. X SE Boreal ► o D A O O K B 0 Offshore Basin A Middle Shelf X Inner Shelf ik x A X X X xo o V " X c O Artinskian A Asselian X Sakmarian A o n ° < n S a jX ° o o Figure 54: Early Permian detrended correspondence analysis of samples described by the relative abundance of ecological categories. A -C displays genera-ecotype ordination plots for samples grouped by (A) paleogeography, (B) depositional environment, and (C) stratigraphic stage. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Axis 2 136 Endobyssate Suspension o Pedunculate O Ecological Category A Samples___________ Suspension \ We4, B el O '4 Reclining Suspension cT\\\ Epibyssate \ \M u6 Suspension \M u7 Mu5 Burrowing O Deposit Epifaunal Grazer Burrowing Suspension Cementing Suspension * Axis 1 Figure 55: Late Carboniferous detrended correspondence analysis of samples described by the relative abundance of ecological categories. Ecological categories and samples are plotted together. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 137 O Ecological Category A Samples___________ Cementing Suspension Endobyssate Suspension Ya3 Burrowing Suspension Gr3 M!1 1 I /a l I Mu2 Pedunculate Suspension Epibyssate Suspension Wa3 Ya2 Ku2 H oi C ol Ya4 Reclining Suspension Epifaunal Grazer G rl Gr5 Axis 1 Figure 56: Early Permian detrended correspondence analysis of samples described by the relative abundance of ecological categories. Ecological categories and samples are plotted together. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 138 TABLE 12A: BRACHIOPOD SPECIMEN INFORMATION FOR THE LATE CARBONIFEROUS GENERA Group Order Genus Jroductjda 'roc uctjc a Jroc uctjc a ' (a c a yrid|( a ^thynaiaa ^ranuda, riferida hotetida Productida Productida Jrthida. M I S 'rot ucti -roc ucti 'roc ucti rroc ucti 'roducti nngulida 'roquctiqa 'roquctiqa 'roductida Trtnotetida Productida ^roquctjda Spiriferifla ^crotretipa iriferida, -lriferm ida odpctida •rtoida. S iriferm ida., yncnonellida Genus Ecological > d e _______ Category* irac irac irac irac Irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac Irac Irac Irac Irac Irac Irac Irac Irac Irac Irac, Irac, Irac, irac, irac irac irac. u o p o c 110 IOC 110 IOC HO IOC 110 JOC n o io< 1 ) 0 IOC 1 1 0 )0( no loc no io( 110 IOC n o io c n o ioc n o io c l t o IOC 1 1 0 )0( 110 JOC no io c no j o c 110 JOC no jo c no jo c 110 JOC no jo c no jo c no jo c no jo c no jo c no jo c no jo c no jo c 110 JOC n o joc 1 ) 0 JOC lio H K 'roc uctic a Jroquctic a Spirifenc a ?uxtc *allip om a . Iiprotonia anChnella ioi\etcs ioristite.s. eiothyridina ^omposila inja ^rurilljvns ^rai erbyiA, ^ictyoclostus jchinoconchus pteletes -imbrinia lustepia,. lystriculina pres an i a . yozlowskja Cutorginella .eptarpsia ■lngula -inoproductus .lssochonetes ' arginitera ' eekcl a esolobus eocnonetes e.o.spimer mella ST an 10 lor e om ra ru er IS nt jm us s oz ,ut S P jno s ar ee es i u : w C u Teo se.os un I ff lec ! ♦Abbreviations: Bur Dep - Burrowing deposit feeders; Bur Susp - Burrowing suspension feeder; Cem Susp - Cementing suspension feeder; Epib Susp - Epibyssate suspension feeder; Epif Graz - Epifaunal grazer; Ped Susp - Pedunculate suspension feeders. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 139 TABLE 12B: M OLLUSC SPECIMEN INFORMATION FOR THE LATE CARBONIFEROUS GENERA Group Order Genus Genus Vo y o V0 V0 V0 y 0 y 0 V0 y 0 y 0 y 0 y 0 y 0 y 0 y 0 y 0 y 0 V0 y 0 y 0 y 0 V0 y 0 y 0 y 0 'lucylpida ' ?id i Anthraconeilo Aviculopecten Aviculobmna iellcroD hon ;dm onaja luphem ites yspira lapnocingulum W leek osp ira ilin a . copsis h.„u Id n $ iS ’aleyolaia ■ ’erm ophorus Phvrpatppleura loglypta jondeV Ecological use use use use use use use use use use use use use use use use use use use use use use use use use pnontida pnyn ^myoidfl montida urchiSonnna rchaeogaslropoda vlurchispniin.a, iellerophontida wurjcnisoniina f Pterioida chaepgastropoda iculoiqa iculoida ., oladomyoida , Vrchaeogastropoda >pnaRnppoda nculQida tjlow a rioida. gpijipida Pterioida , Septi m 0 o « r da m *romytilus o j i n i ( . u u u S S.eptunyalina yti 'seudomonotis Schizodus acu ira ia_ Pur,c « E lb Cem I ?ur,r ♦Abbreviations: Bur Dep - Burrowing deposit feeders; Bur Susp - Burrowing suspension feeder; Cem Susp - Cementing suspension feeder; Epib Susp - Epibyssate suspension feeder; Epif Graz - Epifaunal grazer; Ped Susp - Pedunculate suspension feeders. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 140 TABLE 13 A: BRACHIOPOD SPECIM EN INFORMATION FOR THE EARLY PERM IAN GENERA Group Order Genus Genus Ecological ♦Abbreviations: Bur Dep - Burrowing deposit feeders; Bur Susp - Burrowing suspension feeder; Cem Susp - Cementing suspension feeder; Epib Susp - Epibyssate suspension feeder; Epif G raz - Epifaunal grazer; Ped Susp - Pedunculate suspension feeders. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. rthida. oductida. A cosarina. Anemonaria \ntrojiaria iipafiola M otina ..elebetes . tonetes . tone' .ategory Jedsusp lec s u s 3 red s u s ) lec s u s ) lec s u s ) le c s u s ) le c s u s ) le c s u s ) Jed s u s ) Jed s u s ) le c s u s ) le c s u s ) Jed s u s ) >ed s u s ) lec su s 3 Jed s u s ) le c sus 3 Jed s u s ) Jed sus 3 lec sus 3 lec sus 3 lec sus 3 lec sus 3 Jec sus > Jet sus 3 Jec sus 3 Jed sus 3 le c sus 3 Jec s u s ) Jec s u s 3 Jec Susp Jec sus i Jed sus 3 lec sus 3 >ed sus 3 lec sus 3 Jed sus 3 lec sus 3 lec sus 3 Jed s u s ) lec sus 3 lec sus 3 Jed s u s ) irac irac irac irac irac irac irac irac irac irac irac irac irac irac 3rac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac irac liopoc 1)0 30C 1)0 30C 1)0 30C 1)0 30( HO 30C 1)0 30( 1)0 30C 110 30C 110 30C 110 30C 110 30C HO 30C 110 30( HO 30C 110 301 110 30( 110 30C 110 30( HO 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C 110 30C HO 30( 110 30C 110 30C 110 30C 110 30C 110 30< 110 30( 110 30( HQ 101 m r e l l i d a Jroductjc a Jroquctic a Jroquctic a Jroductjc a Prpductic a Atnyriqic a \thyndic a Jroquctic a Jroductjc a oiriteric a 3irjferic a toductioa )rtnotetida Productida Jrthotetida Atnyridiqa Jro( uctiqa Jroc uctiqa Jroc uctiqa Jroductjda iiriferida rtnQtetida mriferida .brebratulida Jroductjda jijxfjrida Ane eiotnyric ostta ina ompostta omuquia ostelrarina runcella rurithyris emooedys erbyia, ictyoclostus ipranus ustedia lncisius. resam Z1Q W mirera inter ncpsa rbico.eiia rtnoticnia rbiculpidea, , . ermophricpdothyris hipiqom ella ugaria piriierellina qu tes juctiqa ^y n cb o n ellid a quamaria , streptprhynchus itridchoneti [errakea. amiopsis jshrenia 83, P ? lug ?enites erella 141 TABLE 13B: M OLLUSC SPECIM EN INFORMATION FOR THE EARLY PERM IAN GENERA Group Order Genus Amphiscapha Anompnaius Apachefla Astartella Avicu opecten yviculqbjnna Jakevenia ie leropbon . ^alcicahiculana ;uom pnalus . yjDhemRopsis „ Drocingulum 1 yptolega btospira iiasm a , ampnalus Jekosbira ^oli'devcia Pseydomonotis Schizodus, M pUro^alina wilkingia Yunnama. Prodentalium Ecological ~ tggorv* V0 use V0 use V0 use V0 use V0 use V0 use V0 use V0 use y 0 use y 0 use y 0 use y 0 use y 0 use y 0 use y 0 use V0 use y 0 use V0 use y 0 use V0 use y 0 use V0 use V0 use V0 use V0 use y 0 use y 0 use V0 use V0 use . Scaphopod iuom phajiqa luom bhahda Vrchaepgastropoda /encroida noida tjj.tjloida nerioica iellgrpphontida itenou a , luom phahda., 3ellerbphontida , Vrchaepgastropoda Nuculoiaa Archaeogastropoda Archaepgastropoda Momnhanda r urcm nuna luom ph - Pholadomyoida , Archaeogastropoda Vrchaeogastropoda viuculpjaa •te rio id a , fngpnipida ’tefioida lelLerophontida irholaddmyoida , Vrchaeogastropoda >caphopod________ } susp raz jE? F t urdep Jem susp }ur susp “ iB? ♦Abbreviations: Bur Dep - Burrowing deposit feeders; Bur Susp - Burrowing suspension feeder; Cem Susp - Cementing suspension feeder; Epib Susp - Epibyssate suspension feeder; Epif Graz - Epifaunal grazer; Ped Susp - Pedunculate suspension feeders. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 142 TABLE 14: M RPP RESULTS FOR EARLY PERMIAN AND PENNSYLVANIAN ECOLOGICAL A PRIORI GROUPS g roup Comparison T-Statistic* p value enn'sylvanian ennsylvanian Paleogeographic Realms N/A JthostratigraDhiQ Stages -5,66 <U~ Jepositional Environment N/A N/A Sarly P erm ian ’aleogeographic Realms -1 3 6 Q . 10 Jthostraugrabhic. Stages -0.49 0.25 Jepositiorial Environm ent________________ -2.26___________ Q.Q3. *T-statistic describes the distance (or separation) between analyzed groups of samples categorized according to paleogeographic or lithological criteria. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 143 Discussion Most sample plots for both time intervals display significant overlap implying that similar taxa are found within the different paleogeographical locations and depositional environments found in this study. These results are not surprising considering the close proximity of the Northwestern Continental Margin and Northwestern Midcontinent (Figure 45) and the overwhelming number of fossils obtained from these two areas (~99%in Late Carboniferous and 63% in Early Permian). The separation of these samples between stratigraphic stages is interpreted as a meaningful signal (Tables 10 and 11). This implies that faunal patterns change through time between the Moscovian and Gzhelian stages. This result is not surprising either considering the six million year gap between these data (Figure 46). In addition, 96% of the Late Carboniferous data come from the Moscovian stage. Likewise, Early Permian faunal differences occur through time but not to the extent revealed in the Late Carboniferous. These results could be explained by the over abundance of Artinskian stage date (97% of the Early Permian data). Since this data is skewed in terms of paleogeography and stratigraphic age these factors can not be ruled out as important contributors to faunal distribution, they simply can not be tested with this particular data. However, ecological patterns within these data are still meaningful and worthwhile to present. The greatest separation or differences exhibited lies within ecological variation. Both Late Carboniferous and Early Permian analyses indicate that brachiopods trend differently compared to molluscs. Similar results are confirmed in all analyses including samples and ecological analyses (Figure 48, 51, 53, 54). In addition, MRPP results confirm that the two groups differ. The general patterns indicate that pedunculate and reclining suspension feeding brachiopods, tend to overlap with cementing, endobyssate, epibyssate suspension feeding bivalves while burrowing deposit feeders and Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 144 epifaunal grazing gastropods separate away from these genera. Burrowing suspension feeders, although not as abundant, seem to overlap this general distribution described above. Conclusion Ecological variation explains faunal distribution within this late Carboniferous and Early Permian data sets. Differences and similarities between sample distribution relating to paleogeography, depositional environment, and lithostratigraphic stages can mostly be explained by the over-abundance of data in specific categories. For both time periods faunal patterns indicate that pedunculate, reclining, endobyssate, epibyssate, and cementing suspension feeders tend to cluster together. In contrast, compared to the latter group, burrowing deposit feeders and epifaunal grazers separate significantly. This study concludes that faunal distributional patterns are not segregated according to taxonomic differences between brachiopods and bivalves. Rather, this study indicates that some bivalves, particularly epifaunal bivalves, occur in similar condition as brachiopods. The majority of the differences between faunal patterns only occur when burrowing deposit feeders and epifaunal grazers appear in these samples. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 145 Chapter 5: Late Paleozoic Brachiopod Communities vs. Early Mesozoic Brachiopod Communities: A detailed paleoecological analysis through time (Pennsylvanian - Late Triassic). Abstract This study incorporates rigorous quantitative paleoecological analyses to document benthic marine faunas from before and after the end-Permian mass extinction to determine why brachiopods radiate dining the Middle and Late Triassic. Using a total of over 387,000 specimens (i.e., 366,321 from the late Paleozoic and 21,671 from the early Mesozoic), data were analyzed using multivariate statistical analysis to discover the similarities and differences between late Paleozoic and early Mesozoic faunal patterns. Multivariate statistical analysis indicates that ecological variance influences faunal patterns greatly. This result holds true for both the late Paleozoic and early Mesozoic data. A strong segregation between samples dominated by sessile benthos (epifaunal brachiopods and bivalves) and samples dominated by mobile benthos (infaunal bivalves and grazing gastropods) exists. Further examination of faunal patterns reveals apparent taxonomic differences between late Paleozoic and early Mesozoic faunas. Late Paleozoic faunas display greater brachiopod diversity compared to bivalves and major orders present include brachiopod orders such as: Athyridida, Lingulida, Orthida, Orthotetida, Productida and Spiriferinida while one order comprised most bivalves, Nuculoida. In contrast, early Mesozoic faunas display greater bivalve diversity compared to brachiopods and major orders present include brachiopod orders such as: Athyridida, Rhynchonellida, Spiriferinida, and Terebratulida while major bivalve orders consisted of Actinostreon, Nuculoida, Pterioida, Trigonioida, and Veneroida. However, both time intervals display similar ecological patterns, late Paleozoic and early Mesozoic faunas record Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 146 a predominantly sessile benthos mainly composed of stress tolerant taxa. It is speculated that the brachiopod proliferation during the Middle and Late Triassic occurred due to extenuating environmental stress caused by the end-Permian mass extinction. Evidence for change from this sessile, stress tolerant ecology begins to occur in the Late Triassic. As oceanic condition return to normal, high-energy, mobile benthos slowly begin to replace sessile benthos as the dominant marine group, however this data does not record the actual switch in ecology. Thus, it is speculated that this switch occurs later in the Mesozoic. Introduction Brachiopods are one of only seven phyla that span the entire Phanerozoic; their fossil record began in the earliest Cambrian and distant relatives of these ancient individuals occur in our present day deep oceans and seas. Brachiopods tend to be thought of as a part of the “Paleozoic fauna” because the phylum expanded and steadily radiated throughout this time periods. In the carbonate shelf and ramp settings, brachiopod assemblages ranged from onshore to offshore, forming vast pavements, each with their own distinct niche. The close of the Permian, however, recorded the most catastrophic Phanerozoic mass extinction for the phylum, driving four major orders into extinction. After the end-Permian mass extinction, brachiopod genera never reached their former Paleozoic diversity high. However, research indicates that brachiopods begin to radiate in the Middle Triassic and continued to proliferate though the Middle Jurassic (Gould and Calloway, 1980; Sepkoski, 1996). This study aims to determine why brachiopods made a faunal comeback after their near decimation at the Permian-Triassic boundary. To answer this question, benthic marine communities were compared before and after the end-Permian mass extinction. This increase in early Mesozoic brachiopod diversity provides an Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 147 exceptional opportunity to observe the general causes behind the return of these typically “Paleozoic fauna” members. Methods Data Acquisition This literature-based data set comprises information from 27 samples from the late Carboniferous through the Early Permian and 26 samples from the Middle Triassic through the Late Triassic (Figure 57). The late Paleozoic data sets predate the end-Permian mass extinction by approximately 10-12 Ma, therefore, any faunal changes due to the approach of a mass extinction could be avoided (Gradstein and Ogg, 1996). The early Mesozoic data postdates the end-Permian mass extinction by approximately 6.5MA ±4.7 (Gradstein and Ogg, 1996). This time period was chosen for analysis because it documents a diversity increase of brachiopods from the Anisian through the Rhaetian (Figure 58). Important differences in preservational state certainly remain between late Paleozoic and early Mesozoic faunas, especially the difference in the overall numerical abundance between silicified and non- silicified specimens. However, this study incorporates the relative abundance of specimens within samples thereby counteracting any numerical biases introduced by the ease of recovering large sample sizes from silicified Paleozoic locales. Late Paleozoic data were drawn from the Paleobiology Database (http://www. paleodb.org) and early Mesozoic data were drawn from primary literature sources and the Paleobiology Database. In all cases, the original publications were examined to determine whether or not the data met the criteria for inclusion. Since abundance data is known to retain more information compared to presence/absences data, only data sources that recorded numerical counts were included. Samples are defined as closely spaced horizons from the same regional locality, within the similar primary Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 148 G eo ch rD n o lo g y S tr a tig r a p h ic p o sitio n of sa m p les a cco rd in g to p a leo g eo g ra p h ic r e a lm a 2 Period I UJ < u W > $ C/3 NW Cont. Margin NW Mid- Cont. SE Boreal 256 260 269 Early Permian Kungurian s ■ a ” u 3 (/) Artinskian Y a l Y a 2 Y a 3 Y a 4 C ol G rl G r 2 G r 3 W a 3 H oi G r 5 0 Sakmarian K u 2 290 297 303 311 Asselian M u l M u 4 M u 2 3 E £ S 1 Gzhelian M u 5 M u 6 M u7 M u 8 on 013 Pennsylvanian Kasimovian V 2 Moscovian B el W ei W e 2 W e 3 014 | Bashkirian G eoc h r o n clo g y S tr a tig r a p h ic p o sitio n of sa m p les a cco rd in g to p a leo g eo g ra p h ic r e a lm 1 Epoch Stage E. Pacific NW Tethys NE Tethys GES* 205 210 221 Rhaetian Sil G 6 G 2 G 1 ‘5 3 S Norian H4L 1 H 3 3 Camian H 2 H I S i2 F 2 F I ZZo O'XA o " X A X A a £ Ladinian T ol K o l 242 s Anisian P 3 V 2 P 2 V 3 P I G al S 3 S 2 S I K a 3 K a l o Spathian > > 1 Smithian Dien. 248 Gries. Perm. Figure 57: Geochronology from Late Permian through Late Triassic (after Gradstein et al. 2004). Samples are categorized according to their appropriate stage and paleogeographic realm. Samples within stages are not arranged in stratigraphic order. *GES - Germanic Epicontinental Sea Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 149 Brachiopods Bivalves 600 Permian-Triassic Boundary 400 < D > Q Brachiopod resurgence 200 540Ma Present Geological Time Figure 58: Coupled logisitic model depicting general brachiopod and bivalve diversity through time. The brachiopod diversity resurgence spanning the M iddle Triassic through the Late Triassic is circled (after, Sepkoski, 1996). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 150 lithologies. Since samples represent different amounts of time averaging, faunal associations are not considered to represent co-occurrence during life. Instead, these samples represent a long history of information regarding fossil associations and assist in the explanation of faunal compositional differences between different realms and environments. Samples represent benthic, interplatform basin or broad siliciclastic/carbonate platform environments. Each sample consists of at least 200 specimens. Although different authors originally identified these specimens, museum collections and published photographs were compared to confirm taxonomic identification. Original abundance counts were transformed into percent specimen per sample (i.e. 1-100%). In total, this study analyzed 14 late Carboniferous, 15 Early Permian, 13 Middle Triassic, and 11 Late Triassic samples with a total count of 387, 992 specimens. Specimens were categorized into their appropriate group (i.e. brachiopod or mollusc), where they lived in relation to the substrate and their feeding habits. Brachiopods were categorized into two ecological niches: 1) pedunculate suspension feeders; and 2) reclining suspension feeders. Bivalves were categorized into five ecological niches: 1) burrowing deposit feeders; 2) burrowing suspension feeders; 3) cemented suspension feeders; and 4) endobyssate suspension feeders and 5) epibyssate suspension feeders. Gastropods fell into one ecological category: epifaunal grazers. Analytical Methods This study uses Non-Parametric Multidimensional Scaling (NMDS) to investigate faunal patterns and Multi-Response Permutation Procedure (MRPP) to confirm the statistical significance of patterns. NMDS is a method of choice if species composition is determined by factors other than position along a gradient Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 151 (Gauch, 1982). Because different time periods were analyzed together, faunal patterns will undoubtedly be more complex then simply aligning along one axis or gradient, therefore, NMDS was chose in order to determine the variable trends within specific time periods. MRPP is a non-parametric procedure for testing the hypothesis of no difference between two or more groups of entities (McCune, 1997). MRPP was chosen because unlike discriminant analysis and multivariate analysis of variance (MANOVA), MRPP does not assume normality, which is seldom met with ecological data (Biondini et al., 1985). Specimens comprising less than 1% of a sample were deleted to reduce the amount of noise in the datasets and aid in interpreting results. In all analyses, approximately 28% of the data was lost as a result of this operation. Since there is a high degree of variation among specimens within samples, the data were log transformed before analyses. PC-ORD Version 4, software for multivariate statistical analysis of ecological data, preformed both exploratory (NMDS) and confirmatory (MMRP) analyses. Data matrices are composed of compositional data with samples described by taxonomic or ecological percents. In addition to multivariate analysis, percentages of life habits, substrate preferences and orders were calculated for each of the four time periods (i.e., Late Carboniferous, Early Permian, Middle Triassic, and Late Triassic) to track ecological and ordinal patterns through time. Results Multivariate Taxonomic Analysis Using NMDS, all genera were analyzed from the late Carboniferous, late, Early Permian, Middle Triassic and Late Triassic together to determine similarities and differences between the time intervals. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Axis 2 152 0 Late Carboniferous ■ Early Permian # Middle Triassic □ Late Triassic 014 Ku2 0 Ya3 Ya4 Ya2 Gr2 Wa3 We5 W e3 0 JV e2 Wei We4 Mul l^Mu4 S \ Mu6 i5 \ ^ O m k Bel Brachiopod Bivalve G6 H3 □ G2 □ V3 Kol- r P3 F2 □ □ LI □ Ka3 P2 • S ^ ^ K a l Axis 1 Figure 59: Nonparametric multidimensional scaling of samples describing generic, relative abundance patterns. Samples are coded according to their appropriate time intervals. In general, sample plots are dependent on percentage of brachiopods and bivalves. Arrows indicate overall increase of brachiopod abundance compared to infaunal bivalve abundance within the group of samples. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 153 The ordinations plot indicates that the Late Carboniferous samples overlap the most with Early Permian samples (Figure 59). This indicates that some genera occur in both late Paleozoic time intervals. In contrast, Middle and Late Triassic samples differentiate out from the late Paleozoic samples confirming that each Triassic time interval is more taxonomically similar with themselves than with any other group of samples (Figure 59). Table 16 reconfirms that the late Paleozoic samples share more genera between themselves then the early Mesozoic samples. That is, the late Paleozoic samples share 25 genera compared to the 2 genera shared by the early Mesozoic samples. Although the late Paleozoic samples display some similarities, as mentioned above, the MRPP results indicate that the two time intervals are significantly different as are the two early Mesozoic time intervals (Table 15). The spread of samples within their appropriate periods indicates that samples vary within each time interval. When taxonomic and ecologic ratios are examined common patterns between time intervals surface (Table 16). Observations within individual time intervals reveal that samples align according to the percentage of brachiopods versus molluscs and the percentage of epifaunal habit versus infaunal habit. For example, Late Carboniferous samples spread out along Axis 1 (Figure 59). Beginning from left to right, samples on the left generally have a higher percentage of infaunal bivalves and epifaunal grazers (e.g. samples Wei, We 2, We 3, We 4, We 5) (Table 15). As samples continue to the right, brachiopods increase in percentages per sample. For example, sample Wei contains 50% brachiopods, Mu7 contains 66% and sample Bel contains 100% brachiopods. Early Permian samples align similarly to late Carboniferous samples with the exception of sample Wa3 and Gr2. Samples separate along Axis 1 with samples containing abundant gastropods and infaunal bivalves on the left (e.g. sample Ya2, Ya3, and Ya4). Moving to the right, Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 154 TABLE 15: M RPP RESULTS FOR PALEOZOIC AND EARLY M ESOZOIC A PRIORI GROUPS a val“e *T-statistic describes the distance (or separation) between analyzed groups. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 155 TABLE 16: THE RATIO OF EPIFAUNAL GENERA VERSUS INFAUNAL GENERA (IN PERCENTS) t e r 1 6 annal vs. Infaunal opnd:Bivalve:(ia«;trop63~ ieolngical Periods 90:10 mi m m oo J 4 J 5:32:38 5:40:5 5 o ;6? o .ate Carboniferous .ate Carboniferous arboniferous arboniferous arboniferous arboniferous 'arboniferous arboniferous arboniferous arboniferous arboniferous arboniferous Jarboniferous *ate Carboniferous Far vT > en n ian ar :ar ar ar ar ar ar |ar ,ar ,ar ar ,ar ,ar ,ar W teg KC I C C I C C I C C I C C I C C ICC ICC ICC ICC ICC 'ermian 'ermian 'ermian 'ermian 'ermian ’ermian ’ermian ’ermian Permian 'ermian 'ermian 'ermian iaqp. ate ate ate ate ate ate. 'ermian 'ermian .riassic riassic .riassic riassic riassic .riassic .riassic .riassic , riassic .riassic e Triassic * 'riassic riassic .nassic riassic ate. riassic riassic , riassic ate, .riassic a te , riassic a te , riassic a te , riassic "riassic riassic Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 156 although gastropods and infaunal bivalve are present, brachiopods begin to increase in percentages (e.g., Ku2, Yal, and M ul) and mollusc percentages decrease (Table 15). Samples to the extreme right contain 100% brachiopods (e.g. Gr3, H oi, and Gr5). As mentioned, samples Wa3 and Gr2 are exceptions to this overall pattern. This exception is most likely due to the fact that these samples comprise genera only present within their individual samples. Middle Triassic samples align along Axis 1 with abundant brachiopod samples plotting to the left (e.g., samples V2, G al, and Kol) and as samples trend to the right, infaunal bivalves increase in percentages (e.g., samples SI, S2, K al, and Ka3) (Table 15). Late Triassic samples plot more along Axis 2 (Figure 59). Samples containing abundant infaunal bivalves plot near the bottom (e.g., LI, FI, and H2). As samples trend upward, epifaunal bivalve and brachiopod percentages increase within the samples (e.g., H3, G6, and Sil). Ecological Trends Percentages of ecological categories were calculated within the four time intervals to gain a better perspective of ecological patterns through time. Late Paleozoic ecological trends indicate that the Late Carboniferous resembles the Early Permian in terms of categories represented during these intervals (Figure 60A). However, relative percentages change with time. For example, the late Carboniferous comprises nearly 2 times as many burrowing deposit feeder and epifaunal grazers than the Early Permian (Figure 60A). During this time, pedunculate and reclining genera comprise only 13% of the total samples. As time progresses to the Early Permian, burrowing deposit feeders and epifaunal grazers decline and pedunculate and reclining suspension feeders increase to comprise 44% of the total samples. Burrowing and epibyssate suspension feeders both play minor Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 157 H Carboniferous H Early Permian Bur Dep Bur Susp Epib Susp Epif Graz Ped Susp Rec Susp Life Habits B V 3 < D 6 0 CO c < L > U 1- O h ffl M iddle Triassic ■ Late Triassic 0 Bur Dep Bur Susp Cem Susp Epib Susp Life Habits Epif G raz Ped Susp Figure 60: Percentage of generic life habits according to geological stage. (A) Percentage of life habits within two Paleozoic stages, the Late Carboniferous and the Early Permian. (B) Percentage of life habits within two M esozoic stages, the M iddle Triassic and the Late Triassic. Life habit abbreviations are as follows: Bur Dep - Burrowing deposit feeders; Bur Susp - Burrowing suspension feeders; Cem Susp - Cementing suspension feeders; Epib Susp - Epibyssate suspension feeders; Epif G raz - Epifaunal grazers; Ped Susp - Pedunculate suspension feeders; Rec Susp - Reclining suspension feeders. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 158 A. Late Carboniferous B. Early Perm ian n = 3 13,887 n=52,357 D. Late Traissic n= 10,836 C. M iddle Triassic n=10,835 Figure 61: Infaunal and epifaunal trends for each geological period. N ote the large discrepancy when com paring M iddle and Late Triassic pie charts. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 159 roles in the ecological associations during this time (Figure 60A). Infaunality is generally higher within the late Carboniferous as compared to the Early Permian, with a decrease from 38% to 20% (Figure 61 A, B). Early Mesozoic ecological trends generally do not mimic one another (Figure 60B). The Middle Triassic mainly comprises pedunculate and epibyssate suspension feeders. Burrowing and cementing suspension feeders and epifaunal grazers are present but at rather low percentages (i.e., 2-11%). As time moves on, the Late Triassic records an increase in burrowing deposit and suspension feeders, and cementing suspension feeders and a decrease in epibyssate and pedunculate suspension feeders as well as epifaunal grazers. Infaunality substantially increases from 11% in the Middle Triassic to 54% in the Late Triassic (Figure 61C, D). Ordinal Trends In addition to calculating ecological percentages per time interval, I also calculated percentages of orders through time (Figure 62 and 63). Results indicate that bivalve ordinal patterns are similar during the late Paleozoic. Both the Late Carboniferous and Early Permian samples consist mostly of nuculoid bivalves (i.e., 98% and 65%). However, the Early Permian also contains 21% euomphalid bivalves. Other orders, such as Pholadomyoida, Pterioida, Trigonioida and Veneroida, comprise rather small amounts of the total samples and in some case are completely absent (Figure 62A). In contrast, brachiopod orders differ through time Figure 63A). Spiriferid brachiopods comprise 52% of the samples, followed by productids (20%), lingulids (14%) and athyrids (11%). Orthotetid, and spiriferinid brachiopods are present but only comprise 1% each of the samples. Through time, productid, orthid, orthotetid and athyridid brachiopods increase (36%, 20%, 14% and 23%) while spiriferinid and lingulid brachiopods significantly decrease (6% and 0%). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 160 0 3 a < D O U r n C u < D £ ’ - 4 — * 3 E 3 u Carboniferous I Early Permian Nuculoida Pholadomyoida Pterioida Orders Trigonioida Veneroida H M iddle Triassic ■ Late Triassic Actinostreon Nuculoida Pectinoida Pterioida Trigonioida Veneroida Orders Figure 62: Percentage of bivalve orders through time. Actual percentages per order are printed on the graph, stacked younger on the bottom and older on top. (A) Bivalve orders for the Paleozoic geologic stages. (B) Bivalve orders for the M esozoic stages. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 161 > Cumulative Percentage > 3 — t o u > £ c n o\ ^ o o o o o o o o S Carboniferous B Early Permian 6 36 « J99fl^^HKk Lingulida Orthotetida Rhychonellida Spiriferinida dida Orthida Productida Spiriferida Orders B *>| 80 < 0 «> 76 § 60 £ 50 < D 40 + - > C S 3 30 s u 20 10 0- Ath B M iddle Triassic B Late Triassic ^ yridida Rhynchonellida Spiriferinida Terebratulida Orders Figure 63: Percentage of brachiopod orders through time. Actual percentages per order are printed on the graph, stacked younger on the bottom and older on top. (A) Brachiopod orders for the Paleozoic geologic stages. (B) Brachiopod orders for the M esozoic stages. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 162 Early Mesozoic bivalve orders exhibit changes through time (Figure 62B). Pterioid bivalves represent the most dominant bivalve order within the Middle Triassic (54%) followed by veneroid (28%), trigonioid, and pectinoid (7%) bivalves. The Later Triassic records an increase in actinostreon (9%), nuculoid (13%) and veneroid (57%) bivalves and a decrease in pectinoid (0%), pterioid (21%), and trigonioid (0%) bivalves. Early Mesozoic brachiopod orders change somewhat through time (Figure 63B). The Middle Triassic records an almost even amount of rhynchonellid, spiriferinid, and terebratulid brachiopods (28%, 33%, and 30%) and a lesser amount of athyridid brachiopods (8%). Late Triassic order results indicate an increase in terebratulids (54%) and rhynchonellids (36%) and a decrease in athyridids and spiriferinids through time. Discussion First and foremost, multivariate statistics indicate that ecological patterns dictate faunal distributions in both the late Paleozoic and early Mesozoic data. Specifically, sessile benthos (epifaunal brachiopod and bivalve) associations plot separately from mobile benthos (infaunal bivalve and epifaunal grazing) associations. This separation between mobile and sessile benthos is not a novel pattern. Studies of modem brachiopod dispersal patterns in the Mediterranean indicate that brachiopod settlement was largely affected by substrate disturbance by chitons and echinoderms, leaving brachiopods confined to grooves cut into the marble (Asgaard and Bromley, 1991). Much evidence, although indirect, suggests that gastropods and other mobile organisms inhibit the establishment of brachiopod populations by smoothing, ingesting, or bulldozing individuals (James et al., 1992; Noble et al., 1976; Peck, 2001a). Compounding this disruption is the relatively slow growth rate of brachiopods, which probably inhibits a quick recovery in local Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 163 populations. Taking all of this evidence into consideration, it can be suggested that this segregation between sessile benthos and mobile benthos provides evidence that the two groups compete locally. Although ecology dictates faunal patterns, taxonomic patterns differ in the late Paleozoic compared to the early Mesozoic. We see gregarious brachiopods well adapted to a variety of environments from muddy, soupy substrates to more firm substrates dominating while nuculoid bivalves play minor roles in the Paleozoic faunas. The varied sessile ecological life style of the Paleozoic does not carry over to early Mesozoic brachiopods. Instead these “Modem Brachiopods” possess strong pedicles denoting their predominant pedicle attached lifestyle and a more efficient lophophore that allow them to thrive in nutrient and oxygen deficient environments (Sandy, 1995). This conservative brachiopod fauna radiated, along with sessile pectinoid epifaunal bivalves only to be later replaced by mobile nuculoid and veneroid bivalves in the Late Triassic. The question is then: why does diversity switch but general ecology remain the same if ecology dictates faunal patterns? Something else must be affecting these faunas. The faunal patterns displayed here provide evidence that local competition occurs between sessile benthos and mobile benthos in both the late Paleozoic and early Mesozoic, therefore we can rule out competition as the catalyst for faunal change. The only other conspicuous factor is the end-Permian mass extinction. Although the actual cause is still under debate, it is generally accepted that an abrupt negative shift in 6C1 3 values occurred causing a major disruption in the carbon cycle at the boundary. This might have been caused by a single factor or a combination of factors (Berner, 2002; Gruszczynski et al., 1989) including sudden upwelling of stratified sea water releasing toxic amounts of CO2 thereby causing hypercapnia in marine organisms (Knoll et al., 1996), a decrease in the oxygen level Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 164 in atmosphere as a result of methane oxidations (Ryskin, 2003), a temporary pH decrease due to large amounts of CO2 in the atmosphere-ocean system as a result of CO2 release from Siberian Traps (Renne et al., 1995), an extraterrestrial impact in the form of meteorites (Becker et al., 2001) or an asteroid or comet (Kaiho et al., 2001) causing sudden terrestrial and marine extinction leading to a “Strangelove” ocean (Bemer, 2002) in which organic decomposition increased thereby increasing CO2 levels and acid rain. Regardless of what caused this shift, all hypotheses predict an increase in CO2 levels, which would cause a change in ambient CO2 levels in the ocean waters. This increase is coupled with the deposition of extensive black shales and precipitation of carbonate crystal fans in shelf sea settings suggesting extensive anaerobic conditions were widespread during the extinction and persisted for several million years after (Knoll et al., 1996; Pruss, 2004; Pruss and Bottjer, 2004a; Pruss and Bottjer, 2004b; Wignall and Twitchett, 1996; Woods et al., 1999). Lower O2 levels and increased CO2 would affect fauna. It has been suggested that even a small change in oceanic CO2 levels could induce hypercapnic ventilatory chemosensitivities within aquatic organisms (Dejours, 1988; Knoll et al., 1996). Hypercapnia coupled with low O2 levels could produce preferential survival of organism that can ventilate more effectively (Knoll, 1996). In this case, high- energy organisms would fair better and considering the differences in physiology mentioned previously, bivalves would fair better than brachiopod because they posses a higher energy life style. Fossil records indicate that epifaunal bivalves constitute one of the major the Early Triassic disaster groups (Fraiser and Bottjer, 2001; Fraiser and Bottjer, in press; McRoberts, 2001; Schubert and Bottjer, 1995; Twitchett, 1999; Twitchett et al., 2004; Waterhouse, 1983; Yang et al., 1986). This ecological selectivity within surviving bivalves might be explained by the differences in ventilation between epifaunal and infaunal bivalves. Available data on Holocene Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 165 bivalves indicates that epifaunal bivalves ventilate up to an order magnitude more than infaunal bivalves (Cranford and Grant, 1990; Jorgensen, 1990; McRoberts and Newton, 1995). Therefore, epifaunal bivalves can tolerate stressed environments better than infaunal bivalves. Interestingly, McRoberts documents a similar pattern of bivalve ecological selectivity during the recovery from the Triassic-Jurassic mass extinction (McRoberts, 2001; McRoberts et al., 1997; McRoberts and Newton, 1995). Following the Early Triassic, data from this study indicates that more efficient ventilating bivalves (i.e. epifaunal bivalves) and specialized brachiopods that thrive in nutrient and oxygen deficient environments persist in Middle Triassic marine benthic faunas. Together these two stress tolerant groups support the idea that the end-Permian mass extinction affected oceanic conditions thereby affecting faunal patterns into the Middle Triassic. Slowly, high energy, mobile benthos began to replace these stress tolerant sessile benthos. Evidence for this change began within the Late Triassic, however, as other researchers suggests, the complete switch from sessile benthos to mobile benthos probably did not occur until later in the Mesozoic (Gould and Calloway, 1980; Hallam, 1991). Conclusion Comparisons of late Paleozoic and early Mesozoic brachiopod and bivalve dominated associations indicate separation between samples dominated by sessile benthos (epifaunal brachiopods and bivalves) and samples dominated by mobile benthos (infaunal bivalves and grazing gastropods). Further examination of faunal patterns reveals taxonomic differences between late Paleozoic and early Mesozoic faunas. Late Paleozoic faunas display greater brachiopod diversity compared to bivalves. In contrast, early Mesozoic faunas display greater bivalve diversity Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 166 compared to brachiopods and major orders present include brachiopod orders such as: Athyridida, Rhynchonellida, Spiriferinida, and Terebratulida while major bivalve orders consisted of Actinostreon, Nuculoida, Pterioida, Trigonioida, and Veneroida. However, both time intervals display similar ecological patterns. Late Paleozoic and early Mesozoic faunas record a predominantly sessile benthos mainly composed of stress tolerant taxa. It is speculated that the brachiopod proliferation during the Middle and Late Triassic occurred due a faunal “lag effect” resulting from the deleterious environmental conditions that triggered the end-Permian mass extinction. As oceanic conditions return to normal, high-energy, mobile benthos slowly begin to replace sessile benthos as the dominant marine group, however this data does not record the actual switch in ecology. Thus, it is speculated that this switch occurs later in the Mesozoic. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 167 Chapter 6: The Advantage of Incumbency is not just for Contemporary Politicians: Brachiopods and Bivalves, A Story of Incumbency, Mass Extinction, and Key Innovations Abstract Replacement almost certainly does not occur by pure chance and it may not commonly involve competitive extinction. One possible scenario involves two locally competing groups, a mass extinction that dislodges the incumbent, and a key adaptation that gives the invading taxon a higher competitive speciation rate than the clade it is replacing. This hypothesis seems to explain the replacement patterns exhibited by brachiopods and bivalves. Introduction One of the most problematic faunal replacements in evolutionary paleoecology is the post- Paleozoic replacement of rhynchonelliform brachiopods with modern-day bivalves. Many explanations have been put forth ranging from changes in predation patterns and increasing disturbance of sessile benthos through bioturbation and rasping herbivores, to finally the most classic explanation, specific competition for resources ((Donovan and Gale, 1990; Rhodes and Thompson, 1993; Rudwick, 1970; Steele-Petrovic, 1976; Thayer, 1981; Thayer, 1983,1985,1986; Vermeij, 1987). Ideas of exploitation of new ecospace, diversity dependence and species packing have also been used as explanations for this replacement (Bambach, 1985; Bottjer and Ausich, 1986; Miller and Sepkoski, 1988; Sepkoski, 1979, 1984; Sepkoski and Miller, 1985). Lastly, some researchers predict that mass extinction reset the evolutionary pattern of brachiopods and bivalves (Benton, 1987; Gould and Calloway, 1980). Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 168 Increasing evidence suggests that mass extinction plays an important role in many faunal replacements throughout the Phanerozoic, including Late Ordovician brachiopods (Sheehan, 1982), Late Paleozoic mammal-like reptiles (Kemp, 1982), Post-Paleozoic benthos (Gould and Calloway, 1980), Late Triassic ammonoids (Hallam, 1987), Late Triassic tetrapods (Benton, 1983), Late Cretaceous tetrapods (Russell, 1979), Late Cretaceous turtles (Rosenzweig and McCord, 1991), Late Cretaceous bivalves and gastropods (Jablonski, 1986), Late Cretaceous reef- builders (Sheehan, 1985), and Mid-Tertiary carnivorous mammals (Radinsky, 1982). That is, mass extinction creates faunal change such that previously successful adaptations prior to the mass extinction are ineffective for survival during this drastic environmental change. Taking this idea further, Rosenzweig and McCord (1991) examined the replacement of straight-necked turtles and postulated the necessary criteria needed to reproduce the observed faunal patterns. They proposed that the turtle patterns in question can be explained by their incumbent-replacement hypothesis. This hypothesis stresses that the privilege of incumbency, including substantial geographic range, large numbers of organisms, and heavy use of resources, prevents new taxa from gaining a foothold in the community. However, incumbency cannot prevent all invasions. Once extenuating environmental perturbations displace incumbents, most likely through a mass extinction, new species with the slightest local adaptation can better invade the empty niche. Once this novel species fills the vacated niche, natural selection takes over fine-tuning its life history according to its new environment. This paper cites evidence explaining the switch between brachiopods and bivalves and focuses on how incumbency plays an important role in this particular faunal replacement. I present evidence of ecological patterns between the two Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 169 groups and argue that the incumbent-replacement hypothesis explains the patterns recorded in brachiopod and bivalve history. Although many other researchers have stressed the importance of incumbency (Gilinsky and Bambach, 1987; Jablonski, 2000; Patzkowsky and Holland, 2003; Vermeij, 1987, 2001), none have shown evidence linking brachiopod and bivalve patterns with the incumbency-replacement hypothesis. Two different groups, two different adaptive strategies Rhynchonelliform brachiopods and bivalves are two of the few extant groups that extend back to the Cambrian, approximately 550 million years ago. Both groups live in similar marine benthic environments, have similar external morphologies and both filter feed their food. However, the two groups differ drastically in their feeding and respiratory physiology. In general, brachiopods possess low levels of activity, metabolism and growth compared to bivalves and their physiology reflects this type of low energy lifestyle. For example, brachiopods tend to shed unwanted particles individually rather then binding rejected particles with food as observed with some bivalve genera (Shumway et al., 1985; Strathman, 1973). Brachiopods also tend to use less mucus in trapping and transporting food and thus are less energetically expensive compared to bivalves (Jorgensen, 1990; Peck, 2001b; Thayer, 1986). Further observations suggest that brachiopods minimize energy expenditure through feeding strategy. First, one brachiopod feeding characteristic involves laminar flow through its mantle cavity, which reduces drag and energy loss due to turbulence (LaBarbera, 1977). In comparison, bivalves experience higher levels of turbulence within their mantle and therefore expend more energy in feeding-current production (LaBarbera, 1977). Second, brachiopods tend to rotate around the pedicle to orient their anterior/posterior axis perpendicular to flow direction (LaBarbera, 1977). As Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 170 a result, brachiopods use less energy pumping water through the mantle cavity by utilizing the energy from external water flow (Peck, 2001b). Physiological differences between the groups are also exemplified in oxygen consumption rates measured in temperatures ranging from 0°C to 14°C. Results indicate that brachiopods tend to consume significantly less oxygen than bivalves (James et al., 1992; Peck, 2001b). Rhynchonelliform brachiopods are also thought to have extensive capabilities to withstand anaerobic conditions (Hammen, 1977). In addition, single species studies investigating effects of temperature on metabolism suggest that brachiopods are sensitive to temperature changes (Shumway, 1982). Further investigation indicates that brachiopods need a substantial amount of time to acclimate to temperature changes; thus, this suggests that brachiopods take longer to adapt to environmental changes (Peck, 1989). In addition to the stated physiological characteristics, brachiopods tend to have slow muscle reactions, take a long time to process food and have a low metabolic response to that meal (Peck, 2001b). A comparison of living brachiopod and bivalve physiology provides consistent results with the statements above (Rhodes and Thompson, 1993). This study indicates that brachiopods experience lower clearance rates compared to bivalves, which suggests that feeding rates are lower for brachiopods. In addition, brachiopods do not appear to feed effectively at the high algal concentrations exploited by bivalves (Rhodes and Thompson, 1993). The stated evidence above confirms the propensity of brachiopods towards a low energy lifestyle when compared to bivalves. Their different energetic lifestyle is thought to give each group a different competitive advantage. Thayer (1986) states that the energetically efficient lifestyle of brachiopods might give the group a competitive advantage over suspension-feeding bivalves when oxygen and food supplies are limited. With this in mind, one would expect brachiopods to thrive Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 171 in quiet, static environments (e.g., deep marine basins) and bivalves would thrive in a higher energy environment that experiences local variation such as nearshore settings. Physiological energy disparities are not the only characters separating rhynchonelliform brachiopods and bivalves; some bivalves possess the adaptive strategy of burrowing. It is generally understood that the early Paleozoic bivalve adaptive radiation, driven by a hydraulically operated, muscular foot, gave rise to epifaunal and infaunal bivalve groups (Stanley, 1968). The muscular foot proved important to Bivalvia because it gave rise to actively burrowing, infaunal suspension feeders that lived at or near the sediment-water interface, and for some epifaunal bivalves, provided a byssal apparatus for attachment (Stanley, 1968). But, it was not until the Mesozoic Era that a second adaptive radiation occurred. Fusion of the posterior edges of the mantle allowed siphons to form thereby providing a means of feeding and breathing while the bivalve was infaunal. Mantle fusion also provided a tight seal for the mantle cavity during the hydraulic process of burrowing, therefore improving burrowing efficiency (Stanley, 1977). These burrowing and boring siphonates thrived by staying deep below the sediment surface avoiding predators and unfavorable conditions. Without this key adaptation, bivalves could not have utilized the previously unexploited infaunal niche (Stanley, 1977). What are the faunal patterns? For nearly 200 million years, during the Paleozoic, no other group of marine organism surpassed rhynchonelliform brachiopods in terms of diversity and abundance (Boucot, 1981; Sepkoski, 1981; Thayer, 1986). They constitute by far the most common fossil in Paleozoic localities. In their reign as benthic marine dominants, they experimented with numerous body plans and expanded worldwide Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 172 occupying numerous ecological niches. It is generally accepted that such a dominant organism with its substantial geographic range and large abundances, should utilize resources heavily (Gilinsky and Bambach, 1987). Taking this into consideration, it is reasonable to conclude that brachiopods were the major incumbent benthic marine organism during the Paleozoic. In comparison to brachiopods, bivalves played a minor role in benthic communities during the Paleozoic. Even though the major taxa of bivalves were established in the Ordovician and subsequently maintained a global distribution, they remained much less diverse and abundant through most of the Paleozoic (Miller, 1990; Miller and Sepkoski, 1988; Pojeta, 1975). Recent detailed paleoecological analysis of late Paleozoic benthic marine associations documents the taxonomic and ecological relations between the groups. Using abundance data from the Late Carboniferous, Early Permian (i.e., the late Paleozoic data) and Middle and Late Triassic (i.e., the early Mesozoic data), of Nevada, Venezuela, Northern Italy, Austria, Hungary, Slovakia, China, Thailand, and Australia, I examined ordinal patterns and paleoecological patterns via multivariate statistics (Chapters 3 and 4 of this dissertation). In this study molluscs were the most abundant group within the Carboniferous and brachiopods were the most abundant and diverse group within the Early Permian (Figure 64). In terms of ordinal patterns, brachiopod abundance is split between a few orders. For example, within the Carboniferous, spiriferid brachiopods dominate over half of the total brachiopod fauna while the orders Athyridida, Lingulida, and Productida comprise 11-20% of the total fauna (Figure 63 A). The Early Permian records a drop in spiriferid and rise in productid brachiopods. During this time productids are the most abundant order (36%) followed by athyridids (23%), orthids (20%), orthotetids (14%) and spiriferids (6%). The variety of orders present reflects the overall taxonomic diversity of late Paleozoic brachiopods. Ecologies within Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 173 Late Carboniferous n= 313,887 Epifaunal Brachiopods 13% Epifaunal Grazers 48% Infaunal Deposit Bivalves 36% Infaunal Susp. Bivalves Epifaunal Bivalves 0% Early Permian n=52,357 Epifaunal Brachiopods 54% Infaunal Deposit Bivalves 18% Infaunal Susp. Bivalves 2% Epifaunal Bivalves 2% Epifaunal Grazers 24% ■ Infaunal Deposit Feeding Bivalves ■ Infaunal Suspension Feeding Bivalves □ Epifaunal Bivalves □ E pifaunal Grazers ■ Epifaunal Brachiopods Figure 64: Ecological patterns of genera within the Late Carboniferous and Early Permian. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 174 these orders range from pedicle attached life styles (e.g.: athyridid, orthid, orthotetid, rhynchonellid, spiriferid, and terebratulid) to reclining spinose types that used their spines as anchorage in soft substrates (productid) and finally to infaunal burrowing orders (lingulid) (Carlson and Leighton, 2001; Grant, 1981). In contrast the bivalve fauna records a more unimodal signal. Nuculoid bivalves dominate both late Paleozoic time intervals. This predominantly deposit- feeding, shallow-burrowing bivalve does not posses a siphon. Other orders present represent only minor portions of the late Paleozoic group. These suspension feeding orders include the byssally attached pterioid (1-6%) and non-siphonate, infaunal orders: pholadomyoids (1%), trigonoids (1-4%) and veneroids (0-2%) (Figure 62). This data agrees with other studies and indicates that the bivalves present within this dataset had not developed a sophisticated siphon yet (Stanley, 1968; Stanley, 1977). In addition, the noticeable dominance of one order and therefore one general life style, confirms the conclusion that Paleozoic bivalves played a minor taxonomic and ecologic role within benthic communities (Miller, 1990; Miller and Sepkoski, 1988; Pojeta, 1975). Within the early Mesozoic data, brachiopods dominate the Middle Triassic and infaunal bivalves dominate the Late Triassic (Figure 65). The ordinal patterns depict the taxonomic change through time (Figure 62 and 63). In the Middle Triassic, brachiopod dominance is split between three pedunculate orders: Rhynchonellida, Spiriferinida, and Terebratulida ranging from 28-30% (Figure 63). Athyrids were present but at a comparatively lower percentage (8%). The Late Triassic data records the gradual increase of terebratulid (54%) and rhynchonellid (36%) brachiopods, which are the two dominant orders extending into the present day. Epifaunal pterioid bivalves dominate the Middle Triassic data (54%) followed by infaunal veneroids (28%) and trigonoids (12%) and epifaunal pectinoids Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 175 Middle Triassic n= 10,835 Epifaunal Brachiopods 65% Infaunal Deposit Bivalves Infauna, s Bjvalves 0% , ---------- Epifaunal Bivalves 17% Epifaunal Grazers 7% Epifaunal Brachiopods 19% Epifaunal Grazers 4% Epifaunal Bivalves 23% Late Triassic n=l 1,251 Infaunal Deposit Bivalves 10% Infaunal Susp. Bivalves 44% ■ Infaunal Deposit Feeding Bivalves ■ Infaunal Suspension Feeding Bivalves □ Epifaunal Bivalves □ Epifaunal Grazers ■ Epifaunal Brachiopods Figure 65: Ecological patterns of genera within the M iddle and Late Triassic. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 176 (7%) (Figure 61). The Late Triassic records an increase in veneroid, nuculoid, (both infaunal) and actinostreon cementing bivalves, which documents the slow replacement of epifaunal brachiopods by infaunal bivalves. This review of ordinal patterns confirms the major taxonomic distinctions between the late Paleozoic and early Mesozoic faunas represented within this data. General patterns within the late Paleozoic reflect a rather diverse brachiopod fauna. Although there is dramatic fluctuation between Late Carboniferous and Early Permian brachiopod orders, 4-5 orders represent the late Paleozoic brachiopod genera while one order represents the majority of late Paleozoic bivalve genera. As a result, late Paleozoic brachiopods exhibit greater taxonomic diversity compared to the late Paleozoic bivalves. Brachiopod attachment modes vary as well to include reclining mudstickers, pedicle attached individuals, and infaunal burrowers, while shallow, burrowing deposit feeders dominated bivalve ecologies. In contrast, the Triassic depicts different taxonomic and ecologic diversity patterns. Overall diversity trends decrease for brachiopods and increase for bivalves. In the Middle Triassic, only pedunculate brachiopod orders thrive, most of which possess a more sophisticated lophophore (Sandy, 1995, 1998) and sessile epifaunal ecologies dominate bivalve orders. The Late Triassic documents the first time burrowing suspension feeding bivalves reach levels exceeding 40% of the community. Previous multivariate analyses of this data (i.e., Chapters 3 and 4) indicate that paleogeography, age, and depositional environment do not control faunal patterns. Overall, multivariate statistics portray the faunal redundancy within samples and the underlying redundancy within this data is the ecological strategy of individual genera. That is, within the late Paleozoic and early Mesozoic data, results indicate that sample organization is dependant on the abundance of burrowing suspension and deposit feeding bivalves and epifaunal grazing gastropods versus Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 177 pedunculate and reclining suspension feeders and endobyssate, epibyssate, cementing suspension feeders (Figure 59). From here on these two groups will be referred to as mobile benthos (i.e., infaunal bivalves and epifaunal gastropods) and sessile benthos (i.e., epifaunal brachiopods and epifaunal bivalves). The arrows within this figure indicate the gradational change in abundance, within a sample, between mobile and sessile benthos, with the arrowhead pointing towards an increase in sessile benthos. Figure 64 depicts similar results indicating an inverse association between mobile benthos and sessile benthos. For example, the Late Carboniferous ratio of mobile to sessile benthos is 87:13 while in the Early Permian, the ratio decreases to 44:56. Figure 65 depicts a similar pattern of inverse relationship between mobile and sessile benthos for the early Mesozoic data. The Middle Triassic records an 18:82 ratio of mobile to sessile organisms while the Late Triassic displays a 58:42 ratio. Both taxonomic percentages and multivariate analyses conclude that brachiopod associations are segregated according to the ecological distinction between mobile and the sessile genera. This separation between mobile and sessile benthos is not a novel pattern. Studies of modem brachiopod dispersal patterns in the Mediterranean indicate that brachiopod settlement was largely affected by substrate disturbance due to chitons and echinoderms leaving brachiopods confined to grooves cut into the rock (Asgaard and Bromley, 1991). Much evidence, although indirect, suggests that gastropods and other mobile organisms inhibit the establishment of brachiopod populations by smoothing, ingesting, or bulldozing individuals (James et al., 1992; Noble et al., 1976; Peck, 2001a). Compounding this disruption is the relatively slow growth rate of brachiopods, which probably inhibits a quick recovery in local populations. This inverse relationship between sessile and mobile benthos most likely represents evidence of local competition. The patterns exhibited here indicate that Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 178 although local competition initiated segregation between late Paleozoic sessile and mobile benthos, sessile brachiopods still dominated the late Paleozoic fauna. Early Mesozoic patterns indicate that this segregation still existed however, mobile benthos began to gain dominance in the Late Triassic. Therefore, I conclude that the end- Permain mass extinction affected the faunal histories of brachiopods and bivalves. How can we explain this pattern? The incumbent-replacement hypothesis proposed by Rosenzweig et al. (1991) describes a detailed theory for faunal replacement mediated by mass extinction. According to their model, certain criteria are needed to produce replacement due to the advantage of incumbency. First, an incumbent clade is needed. Second, the future invading species needs to live in similar environments as the incumbent species. If the future invading species lives in a similar environment, it will obtain the fine-scale local adaptations that natural selection produces in the local environment, making the future invader the “next best” candidate for that particular local environment. These local adaptations, however, do not give the future invader enough advantage over the incumbent until the incumbent is disturbed. Third, the incumbent needs to be dislodged by an extrinsic mechanism such as large-scale changes in its surrounding environment. Such dramatic, global-scale environmental changes occur during a mass extinction event therefore, the replacement pattern must be directly associated with a mass extinction event. Fourth, a speciation method is needed. That is, an organism must possess a key adaptation that does not necessarily work in displacing the incumbent during its prime, but later, that key adaptation gives them the advantage in utilizing vacated niches. Thus, the future invader will experience high origination rates once established. Lastly, the future invader must diversify faster than the displaced incumbent to prevent the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 179 incumbent from speciating. Otherwise, the incumbent’s adaptations favored during the mass extinction will be selected for and the incumbents will speciate. Once all these criteria are met, the future invader can take-over vacated niches fully and then natural selection works on the new clade making them the new reigning incumbent. How does this model apply to brachiopod-bivalve replacement patterns? This study, in combination with other studies, concludes that brachiopods were the incumbent during the Paleozoic (Boucot, 1981; Sepkoski, 1981; Thayer, 1986). This study also documents that local competition between sessile and mobile benthos existed, therefore establishing that these two groups affected one another’s faunal patterns. Further evidence of this interaction has been concluded from modeling bivalve diversity through time (Miller and Sepkoski, 1988). This study indicates that a coupled logistic model accounts for the observed diversity pattern exhibited by bivalves, which suggests that at least one other taxon interacted with bivalves thereby influencing its faunal history (Miller and Sepkoski, 1988). In addition, the overall dominance of nuculoid bivalves (shallow, non-siphonated burrowers) indicates that bivalves experimented with their hydraulically operated, muscular foot obtained in the Early Paleozoic. As mentioned previously, Stanley (1968) concluded that this adaptation is the key to bivalves’ later success as an infaunal burrower. At this point, we have two of the five criteria needed for the incumbent replacement hypothesis: 1) an incumbent (i.e., brachiopods), and 2) a key adaptation (i.e., bivalve muscular foot). A third criterion is met at the Permian-Triassic boundary. This research, as well as others, indicates that the Permian mass extinction affected brachiopod and bivalve faunal patterns (Bambach et al., 2002; Gould and Calloway, 1980). Brachiopod diversity patterns dramatically dropped at this boundary, never to Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 180 recover to their former Paleozoic highs (Gould and Calloway, 1980). Results here indicate that the late Paleozoic fauna contains a taxonomically diverse brachiopod fauna, in which sessile benthos competed locally with mobile benthos. Even though local competition occurred, brachiopods still reigned as the incumbent groups over bivalves. These faunal patterns changed after the end-Permian mass extinction. In the Middle Triassic, the dominant sessile benthos, composed of epifaunal brachiopods and bivalves, replaced the taxonomic and ecologically diverse brachiopod fauna of the late Paleozoic. Local competition between sessile and mobile benthos still existed during this time, however mobile benthos (in this case infaunal suspension feeding bivalves) slowly replaced sessile benthos (i.e., epifaunal bivalves and brachiopods) through the Middle and Late Triassic. Bambach (2002) confirms these patterns by categorizing higher taxonomic units into passive and active ecological groups and “unbuffered” and “buffered” physiological groups. Diversity patterns indicate that the end-Permian mass extinction reduced the diversity of passive, “unbuffered” taxa (i.e., brachiopods and epifaunal bivalves) dramatically thus proving that this mass extinction affected sessile benthos greatly. In addition, Gould and Calloway (1980) confirm that the Permian-Triassic boundary marks a crucial switch in brachiopod and bivalve diversity trends. Their research, along with others, states that the end-Permian mass extinction depressed brachiopod diversity below bivalves for the first time in their life histories (Fraiser and Bottjer, 2001; Fraiser and Bottjer, in press). Together these studies indicate that the end-Permian mass extinction successfully dislodged the Paleozoic incumbent brachiopods. With the previous incumbents vacated, bivalves utilized the key adaptation of a muscular foot, which resulted in a higher competitive speciation rate. Therefore, bivalves possessed the ability to speciate faster than brachiopods thereby inhibiting Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 181 brachiopods from further Mesozoic speciation. As a result, bivalve origination rates increased (Miller and Sepkoski, 1988). However, the data presented here indicates that not all replacement occurred immediately after the mass extinction. Much of the replacement occurred slowly during background extinction time (i.e., Middle to Late Triassic). Data within this study indicate that replacement just started to equalize within the Late Triassic. Other diversity patterns indicate that brachiopods increased in diversity through the Middle Jurassic and plateaued nearly 70 Ma after the P- T boundary (Gould and Calloway, 1980). Hallam (1991) suggests that Paleozoic survivors did not fully become extinct until the Late Triassic. Following these ideas, this data displays the same pattern suggesting that replacement between brachiopods and bivalves was not fully complete until after the Late Triassic. Conclusions Why did bivalves displace brachiopods as ecological incumbents after the Permian-Triassic mass extinction? Primarily, beyond the likelihood that mass extinction provided ecological opportunities for the establishment of new clades, there must have been selective advantages for heretofore non-siphonated bivalves to require and retain burrowing abilities. Paleobiological research indicates that key adaptations do not cause competitive extinctions. In addition, evidence indicates that biotic replacement is not attributed to pure chance. Evidence presented here suggests that enhanced competitive speciation rates, following the removal of an incumbent clade after mass extinctions, promote the faunal replacement between brachiopods and bivalves. It is concluded that regardless of the predisposed abilities of bivalves to create key adaptations, without the disruption of the incumbent Paleozoic brachiopods, they could not dislodge the incumbents until a major environmental disruption took place (i.e., the end-Permian mass extinction). Once vacated, the Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 182 high-metabolic life style of bivalves in combination with key adaptations enabled them to slowly radiate until they finally replacing brachiopods, sometime after the Late Triassic, as the incumbent marine benthos. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Chapter 7: Summary and Future Research Directions 183 Summary The aim of this research was to test why brachiopods resurge in the Middle and Late Triassic using brachiopod and bivalve dominated data from before and after the end-Permian mass extinction. The first part of this research (Chapter 3) documents Middle and Late Triassic faunas. Here, multivariate analyses indicate that group membership (i.e., brachiopod or mollusc), substrate preference, and generic ecological categories controlled Middle and Late Triassic faunal patterns most significantly. To a lesser extent, paleogeographical location played an important role in sample distribution. Next in Chapter 4, late Paleozoic faunal patterns were documented from the Late Carboniferous and Early Permian. For this analysis, multivariate analyses indicate that pedunculate and reclining suspension feeders (i.e., brachiopods) and endobyssate, epibyssate, cementing suspension feeders (i.e., bivalves) cluster together. In contrast, burrowing suspension and deposit feeders (i.e., bivalves) along with epifaunal grazers (i.e., gastropods) cluster together separate from the later brachiopod-bivalve groups. Thus, brachiopod associations are not segregated according to the taxonomic distinction between brachiopods and bivalves. Instead, within this study, ecological distinction separates brachiopod associations based on the substrate preferences of the particular genera, which is infaunal versus epifaunal. Chapter 5 compares the late Paleozoic patterns with the early Mesozoic patterns. This comparison concluded that the taxonomic structure differed between time intervals. The late Paleozoic fauna consisted of numerous brachiopod orders living in a variety of life styles compared to the one shallow burrowing, bivalve order. In contrast, the Middle Triassic consisted primarily of epifaunal brachiopods and bivalves and as the Late Triassic approached, infaunal Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 184 bivalves slowly replaced epifaunal brachiopods and bivalves. Faunal patterns reveal that the early Mesozoic fauna represents a stress-tolerant, sessile fauna suggesting that conditions causing the end-Permian mass extinction affected oceanic conditions such that stress tolerant faunas continued into the Middle Triassic. Slowly, a high energy, mobile fauna replaced stress tolerant faunas as ecological dominants. Chapter 6 concludes this dissertation by presenting a general hypothesis that explains this faunal replacement of brachiopods and bivalves. Here, due to a combination of incumbency, mass extinction, and key adaptations these two locally competing groups replace one another. Specifically, environmental conditions, which caused the end-Permian mass extinction, dislodged the incumbent brachiopods, and the key adaptation of mantle fusion gave the bivalve taxa a higher competitive speciation rate than brachiopods. Therefore, infaunal suspension feeding bivalves slowly replaced the once incumbent brachiopods as the dominant ecological taxa. Future Research Directions One of the major conclusions from this dissertation is that stress-tolerant faunas dominate the Middle Triassic. To determine whether this faunal lag effect is linked to environmental conditions, it would be interesting to complete geochemical analysis on Middle Triassic sediments and, if possible, on individual benthic fossils to determine if sediments and bottom waters were well oxygenated. If sediments were not well oxygenated one would expect a low levels of bioturbation and low occurrence of infaunal suspension feeding organisms thus enabling epifaunal organisms to thrive. The Permian-Triassic boundary is well documented in terms of geochemical analysis. The Middle and Late Triassic, however, lacks substantial geochemical investigation. To date only one paper from China documents Middle Triassic 6C1 3 values (Payne, 2004). Studies such as this could help piece together Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 185 whether or not environment conditions were limited through the Middle Triassic. Interestingly, the Middle Triassic also records another story of incumbent replacement between red and green algae (Falkowski et al., 2004a; Falkowski et al., 2004b). Here, results indicate the three principal phytoplankton (red algae) clades dominant in modem oceans rose to dominance in the Late Triassic. Perhaps this switch to red algae helped infaunal suspension feeders proliferate. Since marine ecosystems are critically dependent on eukaryotic phytoplankton it would be interesting to investigate the correlation (or lack there of) between primary producers and marine benthos. In general, to fully understand why faunas began radiating in the Middle Triassic through Middle Jurassic would be an interesting endeavor. Another theme in this dissertation is incumbency. One main question came to mind while writing this chapter. What made brachiopods incumbents in the Paleozoic? Where the oceans less productive? Did the oceans possess less oxygen? It would be interesting to complete detailed cerium values or C/S ratios for the Paleozoic in hopes to answer some of these questions. Other interesting projects include reanalyzing brachiopod and bivalve diversities through time. Gould and Calloway (1980) found a general positive association between brachiopod and bivalves diversity trends. According to my results, one would expect a negative correlation. It is predicted that if diversity counts were binned into sessile bivalves and brachiopods versus mobile bivalves, instead of just brachiopods and bivalves, a negative correlation would result. This is important to note because it shows that although competition does not actually cause the replacement, it does occur at a local level and therefore is an integral part of the replacement story. Likewise, Miller (1988) concludes that mass extinction did not affect bivalve diversification. These conflicting results between Miller (1988) and Gould and Calloway (1980) may exist because the end-Permian mass extinction Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 186 affected mobile bivalve more than sessile bivalves. Therefore, if bivalve diversity models were completed for mobile and sessile bivalves (instead of combining the two diversities), results may suggest that mass extinction affects the diversity history of mobile bivalves. This is important to document too because in addition to competition, it would indicate that ecology is another important factor determining faunal replacement patterns. Reproduced with permission of the copyright owner. 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Bonuso, Nicole
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The structure and development of Middle and Late Triassic benthic assemblages
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