Sumatran rhinoceros
The Sumatran rhinoceros is considered the least derived of the extant species, as it shares more traits with its Miocene ancestors. Paleontological evidence in the fossil record dates the genus "Dicerorhinus" to the Early Miocene, 23–16 million years ago. Many fossils have been classified as members of "Dicerorhinus", but no other recent species are in the genus. Molecular dating suggests the split of "Dicerorhinus" from the four other extant species as far back as 25.9 ± 1.9 million years. Three hypotheses have been proposed for the relationship between the Sumatran rhinoceros and the other living species. One hypothesis suggests the Sumatran rhinoceros is closely related to the black and white rhinos in Africa, evidenced by the species having two horns, instead of one. Other taxonomists regard the Sumatran rhinoceros as a sister taxon of the Indian and Javan rhinoceros because their ranges overlap so closely. A third hypothesis, based on more recent analyses, however, suggests that the two African rhinos, the two Asian rhinos, and the Sumatran rhinoceros represent three essentially separate lineages that split around 25.9 million years ago; which group diverged first remains unclear. Recent studies suggest that many specimens attributed to "Dicerorhinus" from the Pleistocene of China actually belong to "Stephanorhinus," a closely related genus. The earliest fossil record of the species is from the Early Pleistocene Liucheng "Gigantopithecus" Cave in Guangxi, China, which consists of a nearly complete mandible with preserved cheek teeth and various isolated teeth.