New information on the pectoral girdle and vertebral column in Lupeosaurus (Reptilia, Pelycosauria)

Abstract

UCLA VP 1651, a new specimen from the Lower Permian Admiral Formation of Archer County, Texas, provides information on heretofore unknown portions of the postcranial skeleton of the large pelycosaur Lupeosaurus. Presacral neural spines are elongate and have a subcircular cross section. Laterally directed tubercles are not present on any of the neural spines. Cervical vertebrae appear to have elongate neural spines and sharply keeled centra. Transverse processes are positioned relatively high above the bases of the centra through the length of axial column. The pattern of tilting of the neural spines is similar to that in the primitive edaphosaur Ianthasaurus hardestii. The proximal end of the first sacral rib contributes significantly to the intervertebral articular facet usually formed by the centra. The sacral ribs do not appear to fuse with one another distally. The ventral clavicular plate is greatly expanded anteriorly. The posterior edge of the subcoracoscapular fossa is very well defined. The available morphological information does not warrant a separate familial designation for the genus Lupeosaurus. Despite the lack of laterally directed tubercles of the neural spines, Lupeosaurus appears to be referrable to the Edaphosauridae. However, in the absence of cranial materials, this association must remain tentative. Although this description adds new information for only a restricted portion of the skeleton, it does appear to confirm the existence of a distinct, albeit rare, pelycosaur from the extensively studied fauna of the Lower Permian.