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 extant terrestrial communities, and 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. In particular, shortly after their first appearance 316 Million years ago, we see rapid evolutionary radiations of reptiles and synapsids during the Late Carboniferous and early Permian. This time period is particularly important for studies of vertebrate evolution on land because evolutionary innovations initiated at this time form the foundations of extant communities and their squamate, chelonian, crocodilian, avian, and mammalian members, as well as those of Mesozoic communities dominated by reptiles like dinosaurs. Similarly, some clades of amphibians underwent rapid and sustained diversification during the Paleozoic as they evolved to a fully terrestrial lifestyle. Dissorophoids are significant and research worthy within this context because they coexisted with amniotes as terrestrial predators before giving rise to lissamphibians (extant amphibians - frogs, salamanders, and apodans). Long term studies of the anatomy, diversity, and evolutionary relationships of Paleozoic terrestrial tetrapods will continue to be part of this proposal because new discoveries have major impacts on our understanding of vertebrate evolution. In this proposal I will take a two-pronged approach. Firstly, I will expand my recent work on dental anatomy, development and replacement and propose to evaluate changes in both taxic and ecological diversity within a phylogenetic framework as reflected by the reconstructed feeding behaviour. I will 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 and coeval terrestrial tetrapods 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 time bins that extend from the late Carboniferous (316 Ma) to the end of the early Permian (272 Ma). Secondly, this new approach will be incorporated with other skeletal variables, especially new neurocranial anatomy derived from multimodal CT data into comprehensive time calibrated phylogenetic analyses. The novel use of ecological and taxic diversity patterns within a phylogenetic framework represents one of the transformative ways in which we approach this important chapter in vertebrate evolution. These analyses will shed light for the first time on the community structure and evolution of tetrapods during the initial stages of terrestrial vertebrate evolution.