Biogeographic distribution and metric dental variation of fossil and living orangutans (Pongo spp.).

The genus Pongo has a relatively richer Quaternary fossil record than those of the African great apes. Fossil materials are patchy in terms of anatomical parts represented, limited almost exclusively to isolated teeth, jaw and bone fragments. Fossil evidence indicates that the genus Pongo had a broadly continuous distribution across the southern part of the Indomalayan biogeographic region, ranging in time from Early Pleistocene to Holocene: southern China (77 fossil sites), Vietnam (15), Laos (6), Cambodia (2), Thailand (4), Peninsular Malaysia (6), Sumatra (4), Borneo (6) and Java (4). Within this distribution range, there are major geographical gaps with no known orangutan fossils, notably central and southern Indochina, central and southern Thailand, eastern Peninsular Malaysia, northern and southern Sumatra, and Kalimantan. The geological time and place of origin of the genus remain unresolved. Fossil orangutan assemblages usually show greater extent of dental metrical variation than those of modern-day populations. Such variability shown in prehistoric populations has partially contributed to confusion regarding past taxonomic diversity and systematic relationships among extinct and living forms. To date, no fewer than 14 distinct taxa have been identified and named for Pleistocene orangutans. Clear cases suggestive of predation by prehistoric human are few in number, and limited to terminal Pleistocene-Early Holocene sites in Borneo and a Late Pleistocene site in Vietnam.