A description of the palate and mandible of Youngina capensis (Sauropsida, Diapsida) based on synchrotron tomography, and the phylogenetic implications

The late Permian reptile Youngina capensis (c. 254 Ma) is a non-saurian neodiapsid whose anatomy has been used to represent the reptilian condition prior to the divergence of Sauria (crown-group reptiles). However, despite being first described over 100 years ago, the anatomy of Youngina remains incompletely documented. Here we use synchrotron x-ray micro-computed tomography to document new features of the palate, braincase and mandible of Youngina. New observations include an anteriorly bifurcating vomer, dentition on the ventral surface of the parasphenoid body and cultriform process, and a strongly convex coronoid eminence. Our anatomical observations suggest that Youngina may represent a more stemward lineage among non-saurian neodiapsids and this is supported by our phylogenetic analysis, which places Youngina as an early diverging neodiapsid. Our research will benefit future studies on saurian origins by providing improved constraints on neodiapsid anatomy prior to the divergence of the reptilian crown group.