Rhinoceros 2021

Rhinoceros 2021 (/raɪˈnɒsərəs/, from Greek rhinokerōs ‘nose-horned’, from rhis ‘nose’, and keras ‘horn’), commonly abbreviated to rhino, is a member of any of the five extant species (or numerous extinct species) of odd-toed ungulates in the family Rhinocerotidae. (It can also refer to a member of any of the extinct species of the superfamily Rhinocerotoidea.) Two of the extant species are native to Africa, and three to South and Southeast Asia.

Rhinoceroses are some of the largest remaining megafauna: all weigh at least one tonne in adulthood. They have a herbivorous diet, small brains (400–600 g) for mammals of their size, one or two horns, and a thick (1.5–5 cm), protective skin formed from layers of collagen positioned in a lattice structure. They generally eat leafy material, although their ability to ferment food in their hindgut allows them to subsist on more fibrous plant matter when necessary. Unlike other perissodactyls, the two African species of rhinoceros lack teeth at the front of their mouths; they rely instead on their lips to pluck food.^[1]

Rhinoceros are killed by some poachers for their horns, which are bought and sold on the black market, and used by people in some cultures for ornaments or traditional medicine.^[2] Although rapidly declining in many regions, East Asia as well as a few other regions^[3] were seen as the largest market for rhino horns. It was seen as a medicine in ancient China (TCM), a belief that was spread widely across to other Asian countries.^{[4][5][6][7][8][9]} By weight, rhino horns cost as much as gold on the black market, making it novel for criminal and illegal poachers.^[10] However, the horns are made of keratin, the same type of protein that makes up hair and fingernails, which have null medicinal properties, despite TCM texts saying that rhino horns were “detoxifiers”.^[11] Rhino horn consumption was also related to status and wealth, with the majority of consumers being older, educated, wealthy men, or those seeking rhino horn ornaments. Demand was driven from sudden wealth, and medicinal misinformation.^[12]

Both African species and the Sumatran rhinoceros have two horns, while the Indian and Javan rhinoceros have a single horn. The IUCN Red List identifies the black, Javan, and Sumatran rhinoceros as critically endangered.

Taxonomy and naming

The word rhinoceros is derived through Latin from the Ancient Greek: ῥῑνόκερως, which is composed of ῥῑνο- (rhino-, “nose“) and κέρας (keras, “horn“) with a horn on the nose. The plural in English is rhinoceros or rhinoceroses. The collective noun for a group of rhinoceroses is crash or herd. The name has been in use since the 14th century.^[14]

The family Rhinocerotidae consists of only four extant genera: Ceratotherium (white rhinoceros), Diceros (black rhinoceros), Dicerorhinus (Sumatran rhinoceros), and Rhinoceros (Indian and Javan rhinoceros). The living species fall into three categories. The two African species, the white rhinoceros and the black rhinoceros, belong to the tribe Dicerotini, which originated in the middle Miocene, about 14.2 million years ago. The species diverged during the early Pliocene (about 5 million years ago). The main difference between black and white rhinos is the shape of their mouths – white rhinos have broad flat lips for grazing, whereas black rhinos have long pointed lips for eating foliage. There are two living Rhinocerotini species, the Indian rhinoceros and the Javan rhinoceros, which diverged from one another about 10 million years ago. The Sumatran rhinoceros is the only surviving representative of the most primitive group, the Dicerorhinini, which emerged in the Miocene (about 20 million years ago).^[15]

A subspecific hybrid white rhino (Ceratotherium s. simum × C. s. cottoni) was bred at the Dvůr Králové Zoo (Zoological Garden Dvur Kralove nad Labem) in the Czech Republic in 1977. Interspecific hybridisation of black and white rhinoceros has also been confirmed.^[16]

While the black rhinoceros has 84 chromosomes (diploid number, 2N, per cell), all other rhinoceros species have 82 chromosomes. However, chromosomal polymorphism might lead to varying chromosome counts. For instance, in a study there were three northern white rhinoceroses with 81 chromosomes.