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.