<i>Varanops brevirostris</i>(Eupelycosauria: Varanopidae) from the Lower Permian of Texas, with discussion of varanopid morphology and interrelationships

ABSTRACT A comprehensive revision of Varanops brevirostris on the basis of a large, well-preserved specimen from a new Lower Permian locality in Texas provides valuable new anatomical information and additional autapomorphies for this varanopid synapsid taxon. These include the loss of the postorbital boss, the presence of a smooth transition between the dorsal and lateral surfaces of the postorbital, hypertrophied basipterygoid processes, the presence of deep, elongate lateral neural spine excavations, posterior dorsal vertebrae with dorsally tapered neural spines, and a deep groove proximal to the femoral fourth trochanter. Furthermore, this specimen is the first fully developed adult specimen of Varanops, and it preserves the most complete lower jaw of the taxon. A revised phylogenetic analysis places V. brevirostris as the sister taxon to the Varanodon-Watongia clade. A stratocladistic analysis assessing varanopid relationships by incorporating a stratigraphic character into the analysis recovers the same topology among varanodontines, but an alternate topology between mycterosaurines and Elliotsmithia longiceps. ACKNOWLEDGMENTS We thank J. Head and D. Evans for their insight and input during the project and for several discussions on varanopids and/or stratocladistics. We are indebted to D. Scott for photographing the specimens, and for providing us with the technical skills needed to complete this project and to L. Tsuji, E. Cheung, and J. Assef for providing the drawings of the postcranial skeleton of TMM 43628-1 (pes excepted). Thanks to J. Fröbisch, N. Fröbisch, K. Folinsbee, and D. Mazierski for several useful discussions and readings of earlier manuscripts, and to Linda Tsuji and an anonymous reviewer for comments that greatly improved the manuscript. Many thanks are owed to R. Burt, J. Cox, and J. Ostlien for collecting, excavating, and kindly donating the specimen to the Texas Memorial Museum. Thanks as well go to W. Langston, Jr., and the Texas Memorial Museum for lending us the specimen. Special thanks to D. Fox for providing us with an early version of the stratocladistic software StrataPhy, prior to its release, and to M. Wills for providing us with access to his Ghosts package for determining stratigraphic congruency metrics. This project was completed thanks to funding from the Natural Sciences and Engineering Research Council of Canada, and Fellowships from the University of Toronto.