Cranial disparity in the non-mammalian synapsida

The evolution of cranial disparity (morphological diversity) in the non-mammalian Synapsida is examined. Chapter 1 addresses the effects of taphonomic deformation on morphometric analysis of non-mammalian synapsids, utilizing the abundant dicynodont Diictodon feliceps as an exemplar. Various types of deformation are described and their contributions to the major axes of variance in a geometric morphometric study of cranial morphology are analyzed. Different styles of deformation are found to have stereotyped effects on cranial morphology as measured by geometric morphometry. Deformational "noise" in analyses overwhelms biological signal at lower (species) levels, but does not mislead higher-level analyses of disparity. Chapter 2 presents a global revision of the dinocephalian clade Anteosauria. Despite containing the first non-mammalian synapsids ever discovered, Anteosauria is one of the most poorly studied synapsid groups. Of the 38 nominal anteosaurian species, nine are considered valid (six from the former USSR, two from South Africa, and one from China). Brazilian specimens assigned to Anteosauria are confirmed as belonging to the group, but are indeterminate to genus. The first comprehensive phylogenetic analysis of Anteosauria, including all valid species, is performed. Two major clades (Syodontinae and Anteosaurinae) within Anteosauria are recognized. Chapter 3 presents a critical review of all amniote taxa from the Tapinocephalus AZ fauna of the South African Beaufort Group. As the earliest therapsid-dominated fauna known from extensive collections, the Tapinocephalus AZ represents an important source of data on the initial radiation of therapsids and their position within Permian terrestrial ecosystems. Based on revised species counts and biostratigraphy, the hypothesis that the Tapinocephalus- Pristerognathus AZ boundary represents a mass extinction (recently correlated with the end-Guadalupian mass extinction in the marine realm) is reevaluated. Chapter 4 analyzes patterns of synapsid cranial morphospace occupation over the entire history of the non-mammalian Synapsida. These analyses address issues of diversity versus disparity in several important aspects of synapsid evolution: morphological diversity of the early, species-poor "pelycosaurs" compared with the speciose later therapsids, disparity in the earliest therapsid faunas, such as the Eodicynodon AZ, to determine rates of morphological diversificatio in the group, the effects of the Permo-Triassic mass extinction on disparity, and patterns of morphospace occupation in the post-extinction Triassic.