A NEW PYLAECEPHALID DICYNODONT (THERAPSIDA, ANOMODONTIA) FROM THE TAPINOCEPHALUS ASSEMBLAGE ZONE, KAROO BASIN, MIDDLE PERMIAN OF SOUTH AFRICA

摘要

We describe Prosictodon dubei, gen. et sp. nov., from the Abrahamskraal Formation, Karoo Basin, Middle Permian of South Africa. Diagnostic characters of P. dubei include postorbitals that slope ventrolaterally and overlap the parietals nearly completely; median anterior palatal ridges that converge with the posterior median palatal ridge, forming a V-shaped structure; caniniform process with an anterior edge that is set off from the palatal rim forming a notch; 'postcanine' teeth present on the maxilla; a ventrally directed transverse flange of the pterygoid with an obtuse posterior margin; a short interpterygoid vacuity that does not reach the level of the palatine pads; a dentary table that forms an elongate grooved surface on the dorsal surface of the dentary, bounded laterally by a low ridge and medially by a tall, thin, dorsally convex blade; 'postcanine' teeth present on the dentary blade; and the absence of a posterior dentary sulcus. A phylogenetic analysis confirms that P. dubei is a member of Pylaecephalidae, although we cannot corroborate that it is the sister taxon of Diictodon feliceps. The holotype of P. dubei was collected low in the Tapinocephalus Assemblage Zone in the northwestern Karoo Basin, near the contact between the Ecca and Beaufort groups, within the stratigraphic range of Robertia but above the ranges of Eodicynodon and Colobodectes. On-going research suggests dicynodonts in the Tapinocephalus Assemblage Zone appeared in sequence (Colobodectes first; Lanthanostegus, Robertia, Prosictodon second; Diictodon and Pristerodon third), in contrast to earlier works that portrayed Diictodon, Robertia, and Pristerodon as occurring throughout the zone.