|Common Name||Square-lipped Rhinoceros|
of rhinoceros. It has a wide mouth used for grazing and is the most social of all rhino species. The white rhinoceros consists of two subspecies: the southern white rhinoceros, with an estimated 17,460 wild-living animals at the end of 2007 (IUCN 2008), and the much rarer northern white rhinoceros. The northern subspecies has very few remaining, with only five confirmed individuals left (four females and one male), all in captivity.
Taxonomy and Evolution
The white rhinoceros of today was said to be likely descended from Ceratotherium praecox which lived around 7 million years ago. Remains of this white rhino have been found at Langebaanweg near Cape Town. A review of fossil rhinos in Africa by Denis Geraads has however suggested that the species from Langebaanweg is of the genus Ceratotherium, but not Ceratotherium praecox as the type specimen of Ceratotherium praecox should, in fact, be Diceros praecox, as it shows closer affinities with the black rhinoceros (Diceros bicornis). It has been suggested that the modern white rhino has a longer skull than Ceratotherium praecox to facilitate consumption of shorter grasses which resulted from the long term trend to drier conditions in Africa. However, if Ceratotherium praecox is in fact Diceros praecox, then the shorter skull could indicate a browsing species. Teeth of fossils assigned to Ceratotherium found at Makapansgat in South Africa were analysed for carbon isotopes and the researchers concluded that these animals consumed more than 30% browse in their diet, suggesting that these are not the fossils of the extant Ceratotherium simum which only eats grass. It is suggested that the real lineage of the white rhino should be; Ceratotherium neumayri → Ceratotherium mauritanicum → Ceratotherium simum with the Langebaanweg rhinos being Ceratotherium sp. (as yet unnamed), with black rhinos being descended from Ceratotherium neumayri via Diceros praecox.
Recently, an alternative scenario has been proposed under which the earliest African Ceratotherium is considered to be Ceratotherium efficax, known from the Late Pliocene of Ethiopia and the Early Pleistocene of Tanzania. This species is proposed to have been diversified into the Middle Pleistocene species Ceratotherium mauritanicum in northern Africa, Ceratotherium germanoafricanum in East Africa, and the extant Ceratotherium simum. The first two of these are extinct, however, Ceratotherium germanoafricanum is very similar to Ceratotherium simum and has often been considered a fossil and ancestral subspecies to the latter. The study also doubts the ancestry of Ceratotherium neumayri from the Miocene of southern Europe to the African species. It is likely that the ancestor of both the Black and the White rhinos was a mixed feeder, with the two lineages then specializing in browse and graze, respectively.
|Northern White Rhinoceros (Ceratotherium simum cottoni)
|Formerly found in several countries in East and Central Africa south of the Sahara, this subspecies is a grazer in grasslands and savanna woodlands. In the world, there are currently only two rhinos of this subspecies left in captivity, along with three that have been returned to a conservancy in Kenya.
Initially, six northern white rhinoceros lived in the Dvůr Králové Zoo in the Czech Republic. Four of the six rhinos (which are also the only reproductive animals of this subspecies) were transported to Ol Pejeta Conservancy in Kenya, Africa, where scientists hope they will successfully breed and save this subspecies from extinction. One of two remaining in the Czech Republic died in late May 2011. The only other captive rhino, also a female, presently lives at the San Diego Zoo's Safari Park in California. Both of the last two males capable of natural mating died in 2014 (one in Kenya on 18 October and one in San Diego on 15 December).
Following the phylogenetic species concept, recent research has suggested the northern white rhinoceros may be an altogether different species, rather than a subspecies of white rhinoceros, in which case the correct scientific name for the former is Ceratotherium cottoni. Distinct morphological and genetic differences suggest the two proposed species have been separated for at least a million years.