THE PERMIAN DICYNODONT COLOBODECTES CLUVERI (THERAPSIDA, ANOMODONTIA), WITH NOTES ON ITS ONTOGENY AND STRATIGRAPHIC RANGE IN THE KAROO BASIN, SOUTH AFRICA

摘要

The dicynodont Colobodectes cluveri was described from a single specimen in 2003. Although the holotype possessed a distinctive combination of primitive, derived, and autapomorphic characters, incompleteness left some aspects of its morphology, such as whether it possessed postfrontal bones, uncertain. Similarly, the holotype was collected near the boundary between the Ecca and Beaufort groups of the Karoo Basin, but the presence of one specimen did not allow a stratigraphic range to be delineated, nor could it be determined whether C. cluveri possessed any biostratigraphic utility. During an ongoing investigation of Tapinocephalus Assemblage Zone dicynodont diversity and biostratigraphy, we identified four new specimens of C cluveri ranging in size from small juveniles to a large adult. These specimens confirm many aspects of the holotype's distinctive morphology, including the absence of postfrontals, paired premaxillae and vomers, and a low foramen magnum. They also offer insights into ontogentic changes in morphology in C. cluveri. Particularly noteworthy is the fact that small individuals lacked erupted tusks, mid-sized individuals such as the holotype possessed small, newly-erupted tusks, and large adults possessed robust tusks. Finally, all C cluveri specimens occur in a narrow interval just above the Ecca-Beaufort contact in the northwestern and western portions of the Karoo Basin. This suggests that the species may be a useful marker for the lowermost Beaufort in areas where the Eodicynodon zone is not preserved, and it fits well with basin development models that reconstruct the Ecca-Beaufort contact as a northeasterly prograding paleo-shoreline.