THE CRANIAL ANATOMY AND RELATIONSHIPS OF THE SYNAPSID VARANOSAURUS (EUPELYCOSAURIA, OPHIACODONTIDAE) FROM THE EARLY PERMIAN OF TEXAS AND OKLAHOMA

The cranial anatomy of the Early Permian synapsid Varanosaurus is rest udied on the basis of previously described specimens from Texas, most importantly the holotype of the type species V. acutirostris, and a re cently discovered, excellently preserved specimen from Oklahoma. Cladi stic analysis of the Eupelycosauria, using a data matrix of 95 charact ers, provides the following hypothesis of relationships of Varanosauru s: 1) Varanosaurus is a member of the family Ophiacodontidae; 2) of th e ophiacodontid genera included in the analysis, Varanosaurus and Ophi acodon share a more recent common ancestor than either does with the m ore primitive Archaeothyris; and 3) a clade containing the progressive ly more derived taxa Edaphosauridae, Haptodus, and Sphenacodontoidea ( Sphenacodontidae plus Therapsida), together with Varanopseidae and Cas easauria, are progressively more distant outgroups or sister taxa to O phiacodontidae. A revised diagnosis is given for Varanosaurus.