Systematics and morphological diversification of the Cordylidae (Squamata)

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The Cordylidae is a species poor but ecologically and morphologically diverse family of lizards endemic to sub-Saharan Africa. Although the majority of the cordylid species are strictly rupicolous (rock dwelling), the family also contains a diverse array of other specialist ecotypes. Due to this concentrated ecological and morphological variation, the family is an excellent system for studying macroevolutionary processes. Previous studies have hypothesized that the majority of diversity in the family evolved rapidly at the base of the viviparous subfamily (Cordylinae), possibly representing an adaptive radiation, but this has not been investigated empirically. The four central chapters of this thesis were designed to be synergistic, with each chapter providing information and helping develop hypotheses in the others. Chapter two places the phylogenetic relationships of the Cordylidae into a temporal framework using relaxed clock Bayesian analyses on an 11 gene, squamate-wide dataset with ten fossil calibrations. These analyses recover the viviparous cordylines as undergoing a period of rapid cladogenesis across the Oligocene-Miocene boundary, radiating into nine well-supported lineages, distributed around the edge of the great escarpment in South Africa. Chapters three and four focused on two different cordylid groups with complicated and unresolved taxomomic histories. By investigating species boundaries within the Smaug warreni species complex (chapter three) and Hemicordylus capensis (chapter four) I address whether the current taxonomy of the family accurately captures the actual species diversity of the family. A combination of phylogenetic, biogeographic and morphological analyses reveals new species within both groups. The fifth chapter attempts to test the hypothesis that the Cordylidae underwent an adaptive radiation following the evolution of viviparity. Morphological variation of the Cordylidae was represented through a combination of standardized ecomorphological measurements and novel, volumetric measurements of osteoderm distributions recovered using High-Resolution CT scanning. Ecological data for known cordylid localities was extracted from multiple commonly used climate layers. Morphological variation was correlated with microhabitat choice, but not with climatic variation. Existing analytical techniques and new methods reveal that the viviparous cordylids experienced an early burst of morphological diversification, while the oviparous subfamily, Platysaurinae, did not. These findings strongly support the hypothesis that the Cordylinae underwent a period of adaptive radiation during the Oligocene, possibly as a result of shifts in the climate and geological uplift of South Africa's Great Escarpment.
xiii, 327 pages : illustrations (chiefly color)
Cordylidae., Morphology -- Variation., Ecophysiology.