Gerald G. Eck

Diversity and frequency distribution of omo group cercopithecoidea

Approximately 6000 cercopithecoid specimens have been recovered from Omo Group deposits of southwestern Ethiopia since 1967. The specimens range in completeness from fragmentary isolated teeth to nearly complete skeletons. The majority of the specimens consist, however, of isolated tecth, fragmentary jaw parts and limb bones. They range in age from c. 3·0 m.y. to c. 0·9 m.y. Both Colobinae and Cercopithecinae have been recovered, with the cercopithecines predominating. The colobine specimens fall into 4 size groups which probably represent taxonomic units. The smallest of the specimens have been assigned to genus Colobus . Of the two middle-sized groups, the smaller is rare and of unknown affinities, while the larger is probably a new genus and species. The largest of the specimens, similar in size to a modern savannah baboon, probably also represents a new genus and species. Six species of cercopithecines have been recovered. Specimens of Cercopithecus and Papio are rare as are those of two species of small Papionini of uncertain affinities. The majority of the specimens belong to the genus Theropithecus with both T. brumpti and T. oswaldi being represented. Cercopithecoid specimens are not evenly distributed through the deposits and preliminary analysis indicates that the differences in frequencies may be due to changes in the environment of the lower Omo basin through time.