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 17,464 individuals in the wild as of the end of 2023, and the much rarer northern white rhinoceros. The northern subspecies is critically endangered and on the brink of extinction; it has only two confirmed left as of 2018 (two females: Fatu, 24 and Najin, 29, both in captivity at Ol Pejeta). Sudan, the world's last known male northern white rhinoceros, died in Kenya in March 2018. White rhinoceros can run up to for very short bursts. They can maintain speeds of around for a good amount of time, and they have good stamina.
Naming
The origin of the name "white rhinoceros" is unknown, but 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 "", which means "wide" in English. The word "wide" refers to the width of the rhinoceros' mouth, distinguishing it from the narrow-lipped black rhinoceros. According to this theory, early English-speaking settlers in South Africa misinterpreted the "" for "white" and the rhino with the wide mouth ended up being called the white rhino. Ironically, Dutch (and Afrikaans) later used a calque of the English word, and now also call it a white rhino ( in Afrikaans). 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 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. It derives from the Greek (), meaning "horn", and (), meaning "beast". The specific epithet, simum, comes from the Greek (), meaning "flat-nosed", referring to the animal's broad, flat snout.
Taxonomy and evolution
The modern white rhinoceros of today was initially thought to be descended from Ceratotherium praecox, which lived around 7 million years ago, with remains found at Langebaanweg near Cape Town. A review of fossil rhinos in Africa by Denis Geraads has suggested, however, 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, given that it shows closer affinities with the black rhinoceros Diceros bicornis. It has been suggested that the modern white rhino's skull, which is longer than that of Ceratotherium praecox, evolved in order to facilitate consumption of shorter grasses that 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), and 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 rhino 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
As of 2021, there were an estimated 15,940 southern white rhinos (Ceratotherium simum simum) in the wild, 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, with 12,968 individuals recorded in 2021. There are smaller reintroduced populations within the historical range of the species in Namibia, Botswana, Zimbabwe, Uganda and Eswatini, while a small population also surviving in Mozambique. Populations have also been introduced outside of the former range of the species to Kenya and Zambia.
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, 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 bulls 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) Rare white rhino dies at safari park. U-T San Diego. Retrieved 25 March 2018. In 2015, the Kenyan government placed the last remaining bull of the subspecies at Ol Pejeta under 24-hour armed guard to deter poachers, but he was put down on 19 March 2018 due to multiple health problems caused by old age, leaving just two cows alive which reside at the Ol Pejeta complex. Staff hope to inseminate the remaining cows with the last bull's semen, although the semen is not preferable due to the age of the rhino.
Following the phylogenetic species concept, recent research has led to the hypothesis that the northern white rhinoceros is a different species, rather than a subspecies of white rhinoceros as was previously thought, in which case the correct scientific name for the former should be Ceratotherium cottoni. Distinct morphological and genetic differences suggest the two proposed species have been separated for at least a million years. However, the results of the research were not universally accepted by other scientists.
Description
The white rhinoceros is the largest of the five living species of rhinoceros. By mean body mass, the white rhinoceros falls behind only the three extant species of elephant as the largest land animal and terrestrial mammal alive today.Cumming, D. H. M., Du Toit, R. F., & Stuart, S. N. (1990). African Elephants and Rhinos: Status Survey and Conservation Action Plan: Action Plan for the Conservation of Biological Diversity 10. IUCN/SSC-AESG, Gland, Switzerland. It weighs more on average than a hippopotamus despite a considerable mass overlap between these two species. It has a massive body and large head, a short neck and broad chest.
The head and body length is in bulls and in cows, with the tail adding another , and the shoulder height is in the bull and in the cow. The bull, averaging about is heavier than the cow, at an average of about . The largest size the species can attain is not definitively known; specimens of up to are considered reliable, while larger sizes up to have been claimed but are not verified. On its snout it has two horn-like growths, one behind the other. These are made of solid keratin, in which they differ from the horns of bovids (cattle and their relatives), which are keratin with a bony core, and deer antlers, which are solid bone. The average weight of a horn is about 4.0 kilograms (8.8 pounds).
The front horn is larger and averages in length, reaching as much as but only in cows. The white rhinoceros also has a noticeable hump on the back of its neck. Each of the four stumpy feet has three toes. The color of the body ranges from yellowish-brown to slate grey. Its only hair is the ear fringes and tail bristles. White rhinos have a distinctive broad, straight mouth which is used for grazing. Its ears can move independently to pick up sounds, but it depends most of all on its sense of smell. The olfactory passages that are responsible for smelling are larger than their entire brain. The white rhinoceros has the widest set of nostrils of any land-based animal.
Genome
The genome size of the white rhinoceros is 2581.22 Mb.Ceratotherium simum genome sequencing at the Broad Institute A diploid cell has 2 x 40 autosomals and 2 sex chromosomes (XX or XY).Stephen J. O'Brien, Joan C. Menninger and William G. Nash: Atlas of Mammalian Chromosomes John Wiley & Sons, Inc., Hoboken 2005, , S. 678
Behavior and ecology White rhinos are grazing herbivores. They are found in grassland and savannah habitat. Preferring the shortest grains, the white rhinoceros is one of the largest pure grazers. It drinks twice a day if water is available, but if conditions are dry it can live four or five days without water. It spends about half of the day eating, one-third resting, and the rest of the day doing various other things. Like all species of rhinoceros, white rhinos enjoy wallowing in mud holes to cool down. The white rhinoceros is thought to have changed the structure and ecology of the savanna's grasslands. Comparatively, based on studies of the African elephant, scientists believe the white rhino is a driving factor in its ecosystem. The destruction of the megaherbivore could have serious cascading effects on the ecosystem and harm other animals.
White rhinos produce sounds that include a panting contact call, grunts and snorts during courtship, squeals of distress, and deep bellows or growls when threatened. Threat displays (in bulls mostly) include wiping its horn on the ground and a head-low posture with ears back, combined with snarl threats and shrieking if attacked. The vocalizations of the two species differ between each other, and the panting contact calls between individual white rhinos in each species can vary as well. The differences in these calls aid the white rhinos in identifying each other and communicating over long distances. The white rhinoceros is quick and agile and can run .