white rhinoceros

The white rhinoceros, white rhino or square-lipped rhinoceros (''Ceratotherium simum'') is the largest extant species 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 19,682–21,077 wild-living animals in the year 2015, and the much rarer northern white rhinoceros. The northern subspecies has very few remaining individuals, with only two confirmed left in 2018 (two females: Fatu, 18 and Najin, 29), both in captivity. Sudan, the world's last known male Northern white rhinoceros, died in Kenya on 19 March 2018 at age 45.

Naming

A popular albeit widely discredited theory of the origins of the name "white rhinoceros" is a mistranslation from Dutch to English. The English word "white" is said to have been derived by mistranslation of the Dutch word "wijd", which means "wide" in English. The word "wide" refers to the width of the rhinoceros' mouth. So early English-speaking settlers in South Africa misinterpreted the "wijd" for "white" and the rhino with the wide mouth ended up being called the white rhino and the other one, with the narrow pointed mouth, was called the black rhinoceros. Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a ''white'' rhino. This suggests the origin of the word was before codification by Dutch writers. A review of Dutch and Afrikaans literature about the rhinoceros has failed to produce any evidence that the word ''wijd'' was ever used to describe the rhino outside of oral use.

An alternative name for the white rhinoceros, more accurate but rarely used, is the square-lipped rhinoceros. The white rhinoceros' generic name, ''Ceratotherium'', given by the zoologist John Edward Gray in 1868, is derived from the Greek terms ''keras'' (κέρας) "horn" and ''thērion'' (θηρίον) "beast". ''Simum'', is derived from the Greek term ''simos'' (σιμός), meaning "flat nosed".

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'' → ''C. simum'' with the Langebaanweg rhinos being ''Ceratotherium'' sp. (as yet unnamed), with black rhinos being descended from ''C. neumayri'' via ''Diceros praecox''.

Recently, an alternative scenario has been proposed under which the earliest African ''Ceratotherium'' is considered to be ''Ceratotherium efficax'' (now synonymous with ''C. mauritanicum)'', 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 '' C. mauritanicum'' in northern Africa, '' C. germanoafricanum'' in East Africa, and the extant ''C. simum''. The first two of these are extinct, however, ''C. germanoafricanum'' is very similar to ''C. simum'' and has often been considered a fossil and ancestral subspecies to the latter. The study also doubts the ancestry of '' C. neumayri'' from the Miocene of southern Europe to the African species.
The ancestor of both the black and the white rhinos was likely a mixed feeder, with the two lineages then specializing in browsing and grazing, respectively. The oldest definitive record of the White Rhinoceros is during the mid-Early Pleistocene at Olduvai Gorge in Tanzania, around 1.8 Ma.

Southern white rhinoceros

There are two subspecies of white rhino: the southern white rhinoceros (''Ceratotherium simum simum'') and the northern white rhinoceros. As of 31 December 2007, there were an estimated 17,460 southern white rhinos in the wild (IUCN 2008), making them by far the most abundant subspecies of rhino in the world; the number of southern white rhinos outnumbers all other rhino subspecies combined. South Africa is the stronghold for this subspecies (93.0%), conserving 16,255 individuals in the wild in 2007 (IUCN 2008). There are smaller reintroduced populations within the historical range of the species in Namibia, Botswana, Zimbabwe, Uganda and Eswatini, while a small population survives in Mozambique. Populations have also been introduced outside of the former range of the species to Kenya and Zambia.

Wild-caught southern whites will readily breed in captivity given appropriate amounts of space and food, as well as the presence of other female rhinos of breeding age. However, for reasons that are not currently understood, the rate of reproduction is extremely low among captive-born southern white females.

Northern white rhinoceros

The northern white rhinoceros or northern square-lipped rhinoceros (''Ceratotherium simum cottoni'') is considered critically endangered and possibly extinct in the wild. Formerly found in several countries in East and Central Africa south of the Sahara, this subspecies is a grazer in grasslands and savanna woodlands.

Initially, six northern white rhinoceros lived in the Dvůr Králové Zoo in the Czech Republic. Four of the six rhinos (which were also the only reproductive animals of this subspecies) were transported to Ol Pejeta Conservancy in Kenya,Northern White Rhinos
olpejetaconservancy.org where scientists hoped they would successfully breed and save this subspecies from extinction. One of the two remaining in the Czech Republic died in late May 2011. 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).Young, Ricky (14 December 2014