Did gorgonopsians survive the end-Permian “Great Dying”? A re-appraisal of three gorgonopsian specimens (Therapsida, Theriodontia) reported from the Triassic Lystrosaurus declivis Assemblage Zone, Karoo Basin, South Africa

Abstract

Gorgonopsians were the dominant carnivores of the late Permian (Lopingian) and it is widely accepted that the clade became extinct at the Permian-Triassic boundary, almost 252 million years ago. However, South African collections house three historically-collected gorgonopsian specimens listed as Early Triassic in age, based on their discovery at localities producing the index fossil Lystrosaurus. Initial reports suggested that these specimens had been reworked from underlying Permian strata, but this possibility was never thoroughly addressed. The possible survival of gorgonopsians into the Triassic would significantly alter our understanding of the end-Permian mass extinction and post-extinction ecosystem dynamics. Here we use Synchrotron X-ray micro-computed microtomography to confirm the identifications and investigate the taphonomic histories of these three specimens. We also relocated the original localities to determine their stratigraphic position. We confirm that all three specimens are indeed gorgonopsians, belonging to the small-bodied genus Cyonosaurus, and that taphonomic assessments do not support reworking. Two of them can be confidently assigned to the latest Permian Lystrosaurus maccaigi-Moschorhinus Subzone of the Daptocephalus Assemblage Zone. In contrast, at the locality listed for the third specimen, NMQR 389, the lowermost outcropping strata belong to the upper Palingkloof Member of the Balfour Formation, which is Early Triassic in age. Despite the evident absence of Permian-aged rocks, other Permian fossils were reported from the same locality, thus casting doubts about the age of NMQR 389. Additionally, differences in preservation style between this skull and the newly collected material at the site cast doubt on its provenance. Although not supporting gorgonopsian survival into the Triassic, these new occurrences expand the range of the genus Cyonosaurus higher up in the extinction zone, increasing the complexity of the ecological turmoil that carnivores endured during “The Great Dying”.