The cranial anatomy and relationships of the synapsid Varabosaurus (Eupelycosauria: Ophiacodontidae) from the early Permian of Texas and Oklahoma

Abstract

The cranial anatomy of the Early Permian synapsid Varanosaurus is restudied on the basis of previously described specimens from Texas and a recently discovered specimen from Oklahoma. Cladistic analysis of the Eupelycosauria, using a data matrix of 95 characters, provides the following hypothesis of relationships of Varanosaurus: 1) Varanosaurus is a member of the family Ophiacodontidae; 2) of the ophiacodontid genera included in the analysis, Varanosaurus and Ophiacodon share a more recent common ancestor than either does with the more primitive Archaeothyris; and 3) a clade containing the progressively more derived taxa Edaphosauridae, Haptodus, and Sphenacodontoidea (Sphenacodontidae plus Therapsida), together with Varanopseidae and Caseasauria, are progressively more distant outgroups or sister taxa to Ophiacodontidae. A revised diagnosis is given for Varanosaurus. -Authors