Sidor, Christian A.Kulik, Zoe T.2023-08-142023-08-142023-08-142023Kulik_washington_0250E_25392.pdfhttp://hdl.handle.net/1773/50240Thesis (Ph.D.)--University of Washington, 2023Much of our understanding of the terrestrial recovery of the end-Permian mass extinction comes from tetrapod assemblages from the Karoo Basin of South Africa but Triassic tetrapods are found in South America, India, Antarctica, and China, as well as nearby basins in Tanzania and Zambia. These assemblages, and the effects that the end-Permian mass extinction had on tetrapod lineages, are an intensely studied subject as they can provide critical information for species survival during turbulent environmental conditions. However, few studies have examined growth strategies and life history patterns which can provide crucial information on a taxon’s survivorship and success following a mass extinction; and the few that have, are almost exclusively based on South African specimens. Because fossilized bone preserves the original bone mineral fiber orientation and bone tissue composition, relative growth rates and markers of skeletal maturity can be inferred from histologic thin sections to reconstruct growth patterns of extinct species. In this study, I used bone histology and body size estimates to investigate how different non-mammalian synapsids adapted their growth trajectory in response to the changed post-extinction environments across Pangea. For the first two chapters, I focused on the dicynodont Lystrosaurus, which had a cosmopolitan distribution across Pangea during early Triassic times but whose growth trajectory has only been examined from southern Pangean species. In my last chapter, I documented variation in bone tissue composition in Middle Triassic cynodonts to test the hypothesis that a mammal-like growth trajectory (i.e., rapid initial growth that plateaus early in ontogeny) is present in some of the earliest members of the mammalian stem ‘recovery fauna’ following the end-Permian extinction. This chapter analyzes cynodont life history across an inferred ontogenetic range of co-occurring species from temporally and spatially constrained deposits and offers an unprecedented opportunity to shed light on the growth trajectories of the last major radiation of the synapsid lineage prior to living mammals.application/pdfen-USCC BY-NC-SAPaleontologyBiologyThesis