Lucas, S.G., et al. eds., 2013, The Carboniferous-Permian Transition. New Mexico Museum of Natural History and Science, Bulletin 60. 161 XENACANTH SHARKS AND OTHER VERTEBRATES FROM THE GERALDINE BONEBED, LOWER PERMIAN OF TEXAS GARY D. JOHNSON Shuler Museum of Paleontology, Institute for the Study of Earth and Man, Southern Methodist University, PO Box 750274, Dallas, Texas 75275-0274; email:
[email protected] Abstract—The Geraldine Bonebed occurs in the Nocona Formation (Wichita Group, Sakmarian age) in Texas. It has historically yielded a large number of mostly complete skeletons of four tetrapod taxa, for which it is famous, and also a diverse flora as well as other vertebrates. Bulk samples of matrix were recently screen-washed and sorted to produce a variety of vertebrate microfossils, including sharks, especially xenacanths. The non-xenacanth sharks are rare and include a petalodont tooth (Janassa?), Helodus sp. (4 teeth) and one partial hybodont tooth. These are all considerably more common higher in the Wichita Group. Only the petalodont and possibly the hybodont and Helodus represent a marine component in the fauna, but the marine faunas are more extensive higher in the Wichita. Also new to the fauna are acanthodians, actinopterygians, Cardiocephalus and Ophiacodon. Among the xenacanths are two typically small Xenacanthus sp. occipital spine fragments, two Orthacanthus sp. occipital spine frag- ments (one small, one very small) and hundreds of Orthacanthus teeth. Orthacanthus texensis teeth are much more common than O. platypternus teeth. Teeth of O. texensis and O. platypternus are comparable in size distributions, as determined by statistical analyses of the tooth-base measurements, to those higher in the Wichita Group.