The past 65 million years of evolution in carnivoran mammals exhibits numerous cases of convergence in ecomorphologies, stereotypical morphologies that represent unique ecological adaptations. Such examples demonstrate the iterative adaptation of distantly related lineages to a few lucrative hypercarnivore (meat specialist) niches. To explore the mechanistic explanations underlying convergent evolution of ecomorphologies, this dissertation documents and reviews recent advances in our understanding of feeding specializations in one particular hypercarnivore niche, the bone-crackers. Bone-cracking specialists evolved at least three times in Carnivora, in the hyaenid, percrocutid, and borophagine canid lineages. These studies in the evolutionary changes of skull shape, enamel microstructure, enamel microwear, and craniodental biomechanics of hyaenids and borophagine canids show that the suite of adaptive morphological characters commonly found in the bone-cracking functional complex evolved in a mosaic manner. Microstructural changes in the enamel were related to increased durophagy as inferred from microwear analysis, followed by continuous skull shape changes toward increased robustness and strength. Subsequently, skull stress dissipation patterns became adapted to handle mechanical demands of durophagy, followed by a split into even more mechanically efficient terminal species versus body size specialists. An updated definition of bone-cracking specialization is presented, and implications for more general understanding of feeding specialization are discussed. An ordered evolutionary sequence of adaptive traits in a functional complex represents a flexible mode of evolution that can accommodate different degrees of specialization in increasingly durophagous lineages, and may serve to explain similar adaptations in other carnivorans and non-carnivoran mammals.
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