Cercopithecids (Cercopithecidae, Primates)

Abstract

New finds from Laetoli have allowed a more detailed assessment of the taxonomy and paleobiology of the fossil ­cercopithecids. Most of the specimens consist of isolated teeth, jaw fragments and postcranial bones from the Upper Laetolil Beds (∼3.5–3.8 Ma), but four specimens are known from the Upper Ndolanya Beds (∼2.66 Ma) and a proximal humerus has been recovered from the Lower Laetolil Beds (∼3.8–4.3 Ma). Four species are represented: Parapapio ado, Papionini gen. et sp. indet., cf. Rhinocolobus sp., and Cercopithecoides sp. Parapapio ado is the most common species. Based on dental size and proportions and facial morphology, Pp. ado can be distinguished from all other species of Parapapio. The postcranial specimens attributed to Pp. ado indicate that it was a slender and agile semi-terrestrial monkey. A few isolated teeth represent a second species of papionin, larger in dental size than Pp. ado. Due to the paucity of the material, the taxon is left unassigned at the genus and species level. A distal humerus attributed to this taxon indicates that it was large terrestrial cercopithecid. The most common species of colobine is referred to cf. Rhinocolobus sp., based on its overall similarities to Rhinocolobus turkanaensis. The material can be distinguished from all fossil colobine species previously recognized from Africa, but without more complete cranial specimens it is not possible to diagnose a new taxon. From the postcranial material it can be inferred that it was generally adapted for arboreal quadrupedalism. The somewhat smaller species of colobine represents a previously undescribed species of Cercopithecoides. The postcranial specimens attributed to this taxon indicate that it was fully arboreal. Analysis of the distribution of the Laetoli cercopithecids provides provisional evidence of spatial patterning and temporal trends. For example, the dentition of Parapapio exhibits a trend to increase in size during the course of the Upper Laetolil Beds. As at other late Miocene and early Pliocene localities older than 3.5 Ma, the Laetoli cercopithecid community is characterized by the absence of Theropithecus and the relatively large proportion of colobines. After 3.5 Ma Theropithecus becomes the dominant cercopithecid at all East African ­localities, and the proportion of colobines declines accordingly.