Patterns of diversification in terrestrial vertebrate evolution

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The fossil record of vertebrates, with preservation of complex skeletons and teeth provides the best evidence of evolutionary dynamics across large temporal scales for investigating the mechanisms and conditions that led to the modern ecosystems. The origin and initial stages of amniote evolution represent the start of a great chapter in earth's history, the conquest of land by vertebrates. Within 6 million years of their first appearance 311 Million year ago (Ma), we see rapid evolutionary radiations that extend to the present, and include extant squamates, turtles, crocodiles, birds, mammals, and many extinct relatives, including dinosaurs. Ongoing research in vertebrate paleontology including the anatomy, taxic diversity, and phylogenetic relationships of early amniotes will continue to be part of the present proposal because new discoveries can have major impacts on our understanding of vertebrate evolution. Here I propose to combine these ongoing investigations with studies of ecological diversity. I therefore plan to evaluate evolutionary changes in both taxic and ecological diversity through time as reflected by their reconstructed feeding behaviour. First, I will integrate for the first time calibrated phylogenetic analyses across clades for a better understanding of patterns of diversification and evolution within communities. I will then examine morphological variation (disparity), including dental and mandibular diversity in comparative, phylogenetic and temporal contexts in order to track the ecological diversification of early amniotes as they evolved to access formerly unoccupied ecospaces and novel food resources. Morphometric analyses of variation in tooth and jaw shape, and size in successive Paleozoic communities will be organized into 8 time bins that extend from the Late Carboniferous (311 Ma) to the Middle Permian (272 Ma). In order to understand the ecological diversity present in these Paleozoic communities I plan to quantify variation in tooth and jaw morphology, and deduce the dietary preferences in each taxon. Several other variables, including cranial and postcranial data may be included in the total disparity analyses. Since extant reptiles show morphological similarities to Paleozoic terrestrial amniotes, squamates can be used as extant model systems. My research group will develop for the first time ecomorphological models that can be applied to early amniotes, and test the hypothetical importance of dietary shifts in the ecological diversification of amniotes. The novel use of combined ecological and taxic diversity patterns represents one of the transformative ways in which we approach this paleobiological research program. These analyses will shed new light on the community structure and evolution of early amniotes during the initial stages of terrestrial vertebrate evolution.