Taxonomy, Phylogeny and Genetics Orangutan
The two orangutan species are the only extant members of the subfamily Ponginae. This subfamily also included the extinct genera Lufengpithecus, which lived in southern China and Thailand 2–8 mya, and Sivapithecus, which lived India and Pakistan from 12.5 mya until 8.5 mya. These apes likely lived in drier and cooler environments than orangutans do today. Khoratpithecus piriyai, which lived in Thailand 5–7 mya, is believed to have been the closest known relative of the orangutans. The largest known primate, Gigantopithecus, was also a member of Ponginae and lived in China, India and Vietnam from 5 mya to 100,000 years ago.:50 Within apes (superfamily Hominoidea), the gibbons diverged during the early Miocene (between 19.7 and 24.1 mya, according to molecular evidence) and the orangutans split from the African great ape lineage between 15.7 and 19.3 mya.(Fig. 4)
The populations on the two islands were classified as subspecies until 1996,:53 when they were elevated to full species status, and the three distinct populations on Borneo were elevated to subspecies. The population currently listed as P. p. wurmbii may be closer to the Sumatran orangutan than the other Bornean orangutan subspecies. If confirmed, abelii would be a subspecies of P. wurmbii (Tiedeman, 1808). Regardless, the type locality of P. pygmaeus has not been established beyond doubts, and may be from the population currently listed as P. wurmbii (in which case P. wurmbii would be a junior synonym of P. pygmaeus, while one of the names currently considered a junior synonym of P. pygmaeus would take precedence for the northwest Bornean taxon). To further confuse, the name P. morio, as well as some suggested junior synonyms, may be junior synonyms of the P. pygmaeus subspecies, thus leaving the east Bornean populations unnamed.
In addition, some fossils described under the name P. hooijeri have been found in Vietnam, and multiple fossil subspecies have been described from several parts of southeastern Asia. It is unclear if these belong to P. pygmaeus or P. abelii or, in fact, represent distinct species.