The Cross River gorilla (Gorilla gorilla diehli) is a critically endangered subspecies of the western gorilla (Gorilla gorilla). It was named a new species in 1904 by Paul Matschie, a mammalian taxonomist working at the Humboldt University Zoological Museum in Berlin, but its populations were not systematically surveyed until 1987. It is the most western and northern form of gorilla, and is restricted to the forested hills and mountains of the Cameroon-Nigeria border region at the headwaters of the Cross River (Nigeria). It is separated by about from the nearest population of western lowland gorillas (Gorilla gorilla gorilla), and by around from the gorilla population in the Ebo Forest of Cameroon. Estimates from 2014 suggest that fewer than 250 mature Cross River gorillas remain, making them the world's rarest great ape. Groups of these gorillas concentrate their activities in 11 localities across a range, though recent field surveys confirmed the presence of gorillas outside of their known localities suggesting a wider distribution within this range. This distribution is supported by genetic research, which has found evidence that many Cross River gorilla localities continue to maintain contact through the occasional dispersal of individuals. In 2009, the Cross River gorilla was finally captured on professional video on a forested mountain in Cameroon. Description The Cross River gorilla was first described as a new species of the western gorilla by Paul Matschie, a mammalian taxonomist, in 1904. Its morphological distinctiveness was confirmed in 1987. Subsequent analyses of cranial and tooth morphology, long bone proportions and distribution demonstrated the distinctiveness of the Cross River gorilla and it was described as a distinct subspecies in 2000. When comparing the Cross River gorilla to western lowland gorillas, they have noticeably smaller palates, smaller cranial vaults, and shorter skulls. The Cross River gorilla is not known to differ much in terms of body size or limb and bone length from western lowland gorillas. However, measurements taken from a male suggest that they have shorter hands and feet and have a larger opposability index than western lowland gorillas. According to Sarmiento and Oate's study published by the American Museum of Natural History, the Cross River gorilla has been described as having smaller dentitions, smaller palates, smaller cranial vaults, and shorter skulls than western lowland gorillas. The Royal Belgian Institute of Natural Sciences depicted the Cross River gorilla as the largest living primate with a barrel-chest, relatively even hair,