ABSTRACT

A kannemeyeriiform dicynodont is described on the basis of an occipital plate from the upper Fremouw Formation (Middle Triassic) Gordon Valley locality in the Beardmore Glacier region of Antarctica. The Antarctic specimen is comparable in size to Kannemeyeria simocephalus from the well-known Cynognathus Assemblage Zone of the Beaufort Group of South Africa, and represents the largest therapsid currently known from the upper Fremouw Formation. The presence of an occipital condyle with distinct contributions from the exoccipital and the basioccipital; a wide, tri-radiate occipital condyle; and a well-developed tympanic process of the paroccipital, which is situated below the level of the occipital condyle, represent a combination of character states hitherto unknown among Kannemeyeriiformes. Combined with the possible autapomorphic feature of slender, dorsoventrally elongate basal tubera, this may suggest the Antarctic specimen represents a new kannemeyeriiform taxon. This specimen represents the most complete, and only the fourth definitive, dicynodont specimen known from the upper Fremouw Formation, and the contradictory phylogenetic character data from these specimens adds support for the presence of multiple (at least two) kannemeyeriiform taxa within the upper Fremouw tetrapod assemblage. Taken together, these kannemeyeriiform specimens provide additional support for a correlation with the Cynognathus Assemblage Zone, particularly the Trirachodon-Kannemeyeria or Cricodon-Ufudocyclops subzones (= subzones B or C), as well as an Anisian or younger age for the upper Fremouw tetrapod fauna.

摘要

根据南极比尔德莫冰川地区的弗雷穆（Fremouw）组（中三叠世）戈登谷地区的枕板，描述了一个坎尼迈耶二叉齿。南极标本可比在尺寸上肯氏兽老年低额从知名犬颌兽属南非博福特集团的集合地带，代表着目前从弗雷莫夫地层上部已知的最大的巨石怪。枕骨dy的存在与枕骨和枕骨的贡献明显不同；宽的三辐射枕骨con; 位于枕骨the水平以下的枕骨发达的鼓膜过程代表了迄今尚不为人所知的性状组合。结合细长，背腹延长的基部块茎的可能的亚种形特征，这可能表明该南极标本代表了一种新的象鼻虫类群。该标本代表了上弗雷莫夫组中已知的最完整，唯一的第四个双叉齿标本，这些标本的相互矛盾的系统发育特征数据增加了对在上部Fremouw四脚架组合中存在多个（至少两个）坎尼梅耶类群的支持。综上所述，这些kannemeyeriiform标本提供了与犬颌兽属组合带，特别是Trirachodon -肯氏兽或Cricodon - Ufudocyclops子区（=子区域B或C），以及一个或安尼低龄用于上部Fremouw四脚动物。