Morphological Evolution and Diversification in the Earliest Herbivorous Tetrapod

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The origin of herbivory in tetrapods (land vertebrates) during the Carboniferous was a crucial event in the establishment of terrestrial vertebrate ecosystems. Herbivory had evolved independently at least eight times by the end of the Paleozoic, and these convergent evolutionary origins provide an ideal case study for examining patterns of morphological evolution, convergence and partitioning during adaptive radiations. An adaptive radiation is the morphological diversification among ecologically-relevant traits that occurs when lineages exploit a new adaptive zone. The new adaptive zone may be created by: a “key innovation” allowing the clade to access previously unused resources; the appearance of a new resource; or the extinction of the previous occupants of the adaptive zone. Paleozoic herbivorous tetrapods provide an opportunity to study all three modes. Numerous morphological innovations are documented in the fossil record to allow exploitation of plant matter. Plants underwent several diversification and turnover events during the Carboniferous and Permian, potentially providing new material to be exploited. Finally, an extinction event dubbed Olson’s extinction at the end of the Kungurian stage provides an opportunity to study the radiation of new herbivorous lineages following a mass extinction. In this project, I aim to answer three questions: Are patterns of craniodental evolution in Paleozoic herbivores consistent with the predictions of adaptive radiation models? Do the independent, contemporaneous origins of herbivory show ecomorphological differentiation consistent with niche partitioning during adaptive radiations? Are patterns of morphological diversity and species richness in Paleozoic herbivores related to the diversification patterns of plants? These questions will be examined using a wide range of methods for quantifying evolution. Discrete character data will be examined using recently-proposed statistical methods to identify trends in morphological diversity variation in rates of character change. Paleozoic herbivore skulls will be landmarked to quantify skull shape, and this shape data will be used to assess morphological overlap between the different clades of Paleozoic herbivores. Species-richness estimates both of herbivores and plants, corrected for incomplete sampling, will be compared to identify interactions between the two. This research aims to greatly improve our understanding, not only of the critical period in the establishment of terrestrial ecosystems, but also the mechanisms underlying adaptive radiations.