A new large gomphodont from the Triassic of South Africa and its implications for Gondwanan biostratigraphy

A partial skull (BP/1/7976) of a very large cynodont from the Middle Triassic <i>Cynognathus</i> Assemblage Zone (<i>Cricodon-Ufudocyclops</i> subzone) of South Africa is described. The specimen represents a new gomphodont taxon, <i>Impidens hancoxi</i>, gen. et sp. nov., diagnosed by five sectorial teeth constituting just over half of the length of the upper postcanine tooth row, and enlarged canine and incisor teeth. BP/1/8123, a skull fragment also from the <i>Cricodon-Ufudocyclops</i> subzone, and AMNH FARB 24421, a partial skull from the upper Fremouw Formation of Antarctica, are also referred to the new species. The presence of this taxon in both the upper Fremouw Formation and <i>Cricodon-Ufudocyclops</i> subzone strengthens evidence of biostratigraphic correlation between these units. <i>Impidens hancoxi</i>, with an inferred skull length of up to 460 mm, was a large-bodied and likely omnivorous gomphodont, and may have played the role of apex predator within the tetrapod fauna of the <i>Cricodon-Ufudocyclops</i> subzone.

本文记述了一件产自南非中三叠世（Middle Triassic）犬颌兽（Cynognathus）组合带下的Cricodon-Ufudocyclops亚带（Cricodon-Ufudocyclops subzone）的大型犬齿兽类（cynodont）部分头骨标本（BP/1/7976）。该标本代表一个新的柱齿型犬齿兽类（gomphodont）类群——汉考克伊匹登兽（Impidens hancoxi），新属新种（gen. et sp. nov.），其鉴别特征为：5枚刃形齿（sectorial teeth）占据上颌后犬齿齿列（postcanine tooth row）总长的一半以上，且犬齿与门齿均显著增大。另有两件标本亦被归入该新种：一件是同样产自Cricodon-Ufudocyclops亚带的头骨碎片BP/1/8123，另一件是产自南极洲弗里莫组（Fremouw Formation）上部的部分头骨AMNH FARB 24421。该类群在弗里莫组上部与Cricodon-Ufudocyclops亚带中均有分布，这一发现强化了这两个地层单元之间的生物地层对比（biostratigraphic correlation）证据。汉考克伊匹登兽（Impidens hancoxi）的推测头骨长度可达460毫米，属于大型柱齿型犬齿兽类，食性大概率为杂食性，且可能在Cricodon-Ufudocyclops亚带的四足动物群（tetrapod fauna）中充当顶级捕食者（apex predator）。