A remarkable cranium of Plesiopithecus teras (Primates, Prosimii) from the Eocene of Egypt.

Between 1991 and 1993 specimens of a highly distinctive primate, named Plesiopithecus teras [Simons, E.L. (1992) Proc. Natl. Acad. Sci. USA 89, 10743-10747], were found at site L-41 in late Eocene deposits of the Fayum Depression, Egypt. The most important of these specimens consists of a nearly complete skull, which facilitates the evaluation of affinities of this primate. Characteristics of the known material now demonstrate that Plesiopithecus is a prosimian, although mandibular molar morphology, in particular, bears similarity to that in molars of archaic members of Anthropoidea. Plesiopithecus has a postorbital bar but lacks postorbital closure, it has upper molars without hypocones, and it may retain four lower premolars. Its familial rank was considered incertae sedis by Simons [Simons, E.L. (1992) Proc. Natl. Acad. Sci. USA 89, 10743-10747]; it can now be demonstrated that Plesiopithecus justifies establishment of a new family and superfamily. The new superfamily apparently lies closer to the toothcomb prosimians (strepsirhines) than to any other known primate group. Under this interpretation the enlarged, procumbent tooth in the jaw of Plesiopithecus is homologous to either the lateral incisor or the canine of the prosimian toothcomb. IMAGES:

1991年至1993年，研究人员在埃及法尤姆凹陷（Fayum Depression）的始新世晚期地层L-41遗址，发现了一件辨识度极高的灵长类标本——近猿（Plesiopithecus teras）[西蒙斯，E.L.，1992，《美国国家科学院院刊》，89卷：10743-10747]。其中最具科研价值的标本为近乎完整的头骨，这为解析该灵长类的亲缘关系提供了关键支撑。基于现有标本的特征分析，现已证实近猿属于原猴类（prosimian），尽管其下颌臼齿形态，尤其是细节特征，与类人猿亚目（Anthropoidea）古老类群的臼齿存在一定相似性。近猿具有眶后棒（postorbital bar）但不具备眶后闭合（postorbital closure）结构；其上颌臼齿无次尖（hypocones），且可能保留4枚下前臼齿。西蒙斯曾将该类群的科级分类地位判定为分类位置未定（incertae sedis）[西蒙斯，E.L.，1992，《美国国家科学院院刊》，89卷：10743-10747]；而如今的研究结果表明，近猿类群完全足以建立全新的科与总科。该新总科与梳状牙原猴类（toothcomb prosimians，即strepsirhines）的亲缘关系，相较于其他已知灵长类类群更为紧密。据此演化假说，近猿颌骨中膨大且前倾的牙齿，与原猴类梳状牙结构中的外侧门齿或犬齿为同源器官。图像：