Evolution, morphology and paleobiology of the pareiasauria and their relatives

Parareptilia is a diverse clade of Paleozoic and early Mesozoic amniotes, sistergroup to the eureptiles within Reptilia. The role and importance of parareptiles in Permian terrestrial ecosystems has been the subject of increased study in recent years. The debate regarding the origin of turtles brought more attention to the group, however many of its members are still poorly-known. Pareiasauria, a widely-distributed and speciose parareptile clade were significant members of Late Permian ecosystems, but despite their prominence, very few taxa have been described in detail. This thesis will undertake a description of some poorly-known parareptilian taxa, using the data to reassess the relationships of parareptiles, with information gained about the phylogeny of the group serving as the basis to assess evolutionary trends within the clade. The nycteroleters have recently become the focus of increased attention, owing to their recently-discovered sister-group relationship to pareiasaurs and the discovery of an impedance-matching ear in members of the group. The Kotel’nich locality in central Russia preserves a diverse fauna that includes the pareiasaur Deltavjatia vjatkensis and the nycteroleter Emeroleter levis. This latter taxon was previously known from only isolated crania, but recent excavations have produced additional material, which includes wellpreserved postcranial remains, allowing a complete redescription of the taxon. A reassessment of the Russian nycteroleters results in the synonymy of Tokosaurus perforatus with Macroleter poezicus. The morphological information was included in a phylogenetic analysis of parareptilian relationships using both parsimony and Bayesian inference. The monophyly of the nycteroleters is supported by parsimony, but is not supported in the Bayesian analysis, and the genus Bashkyroleter appears paraphyletic. A monophyletic clade consisting of the nycteroleters and pareiasaurs, here termed Pareiasauromorpha, is supported by all methods. Parasaurus geinitzi von Mayer, 1857 based on two type specimens consisting of exclusively postcranial material from the Late Permian Kupferschiefer deposits of Germany was the first pareiasaur. Other fragmentary material has subsequently been assigned to the species including a partial skull, however, there is no common anatomical material linking the postcranial material of the types with this cranium. The presence of four to five sacral ribs combined with the swollen neural arches of the dorsal vertebrae allow the recognition of the postcranial remains as pareiasaurian, however examination of the lectotype specimen of Parasaurus reveals no autapomorphic features that can positively identify this material as a distinct taxon. The skull of Parasaurus is small for a pareiasaur, and was assigned to the Pareiasauridae primarily on the presence of distinctive multicusped, leaf-shaped teeth, but apart from the distinctive teeth and high number of sacral ribs, there is little to definitively classify this animal as pareiasaurian. One of the three known pareiasaurs from Russia, well-preserved material of Deltavjatia vjatkensis from the Kotel’nich locality is described in detail. The taxon is characterized by a distinctive pattern of sculpture and the exaggerated embayment of the skull roof resulting in the dorsal exposure of the braincase. Postcranially, Deltavjatia shows aspects of the morphology such as the pattern of osteoderms shared with the Tapinocephalus Assemblage Zone pareiasaurs, and other aspects, such as the forwardslanting pointed blade of the ilium with younger, more derived forms. The well-preserved material of the taxon spans a wide size-range, allowing interpretations to be made about growth patterns. A geometric morphometric analysis of the skull roof of Deltavjatia reveals an allometric increase in snout length along with an increase in postorbital area. Additional specimens would help to strengthen results, but this analysis can serve as a basis for looking at morphological trends within pareiasaurs. Integrating the morphological information of the nycteroleters, Parasaurus and Deltavjatia acquired in previous chapters, a reassessment of the relationships of Pareiasauromorpha using both parsimony and Bayesian methods of phylogenetic inference recovers similar topologies in both cases. In the Bayesian analysis, four analyses were completed, with and without a gamma-shaped parameter and with and without the inclusion of autapomorphies. The recovered topologies are consistent with previous phylogenies of pareiasaurian relationships, although Parasaurus falls more basally in this analysis. None of the resulting cladograms are well-supported indicating that more data is needed, but the topologies are relatively consistent with the stratigraphic record, with indices comparing relatively well with those of other reptilian clades. A stratocladistic analysis recovers a similar topology, though slightly longer, than that of the strictly morphological phylogenetic analyses, and a search for ancestors in a stratocladistic analysis including autapomorphies reveals that certain taxa, primarily those with no identified autapomorphies, are consistently placed as ancestral. Their widespread distribution in the Late Permian along with their relatively high diversity make pareiasaurs ideal indices of dispersal and biogeography among Permian tetrapods. A biogeographic analysis of pareiasauromorph taxa recovers complex and reticulated patterns of dispersal and vicariance, including multiple dispersal events into both Russia and China. These complex patterns are consistent with those seen in other Late Permian groups, though few events are shared by all clades. The analysis also reveals that many geographical areas have complex histories, suggesting that a search for smaller divisions within areas should be attempted.