Rhinoceros (genus)

Rhinoceros
Indian rhinoceros (Rhinoceros unicornis)
Scientific classification
Kingdom: Animalia Phylum: Chordata Class: Mammalia Order: Perissodactyla Family: Rhinocerotidae Genus: Rhinoceros Linnaeus, 1758
Species
Rhinoceros unicornis Rhinoceros sondaicus

The genus Rhinoceros of the family Rhinocerotidae includes the one-horned rhinoceroses, of which there are two extant species: the Indian rhinoceros (R. unicornis) and the Javan rhinoceros (R. sondaicus). These are characterized by one horn (actually thickly matted hair) on the upper snout.

The Javan rhinoceros is one of the most endangered large mammals in the world with only 60 individuals surviving, in only two known locations: Java (Indonesia) and Vietnam.

Overview and description

The Rhinoceros genus is one of four extant genera of rhinoceroses in the rhinoceros family (Rhinocerotidae), the others being Ceratotherium (white rhinocerosis, C. simum), Diceros (black rhinoceros, Diceros bicornis), and Dicerorhinus (Sumatran rhinoceros, Dicerorhinus sumatrensis). All extant rhinoceroses are large, thick-skinned herbivores, with three functional toes on each foot, and either one or two horns on the upper snout. Members of the Rhinoceros genus are characterized by just one horn on the upper snout, while the other extant genera are represented by species with two horns, although one of the Sumatran rhino's horns typically is a stub. These projections are not true horns, but rather are epidermal derivatives, composed of a solid mass of thickly matted hair that grows from the skull without skeletal support.

The word "rhinoceros" is of Greek origin; rhino, meaning "nose," and cero, meaning "horn."

The two extant species in the Rhinoceros genus are both found in Asia, the Indian rhino (R. unicornis) and the Javan rhinoceros (R. rhinoceros). The Sumatran rhinoceros also is found in Asia, but the other two extant rhinos are found in Africa.

Evolution

The Indian and Javan rhinoceros first appear in the fossil record in Asia around 1.6 million to 3.3 million years ago. Molecular estimates, however, suggest the species may have diverged much earlier, around 11.7 million years ago (Rougard et al. 2001; Xu et al. 1996). Although belonging to the type genus, the Indian and Javan rhinoceros are not believed to be closely related to other rhino species. A detailed cladistic analysis of the Rhinocerotidae placed Rhinoceros and the extinct Punjabitherium in a clade with Dicerorhinus, the Sumatran rhino. Other studies have suggested the Sumatran rhinoceros is more closely related to the two African species (Cerdeño 1995). The Sumatran Rhino may have diverged from the other Asian rhinos as far back as 15 million years ago (Lacombat 2005; Dinerstein 2003).

Fossils of Rhinoceros unicornis appear in the Middle Pleistocene. In the Pleistocene (1,808,000 to 11,550 years BP), the Rhinoceros genus ranged throughout Southeast Asia and South Asia, with specimens located on Sri Lanka. Into the Holocene, some rhinoceros lived as far west as Gujarat and Pakistan until as recently as 3,200 years ago (Laurie et al. 1983).

Indian rhinoceros

The Indian rhinoceros (Rhinoceros unicornis) is found in Nepal, Bhutan, Pakistan and in Assam, India, in tall grasslands and forests in the foothills of the Himalayas. Also known as the great one-horned rhinoceros and the Asian one-horned rhinoceros, it is very large, almost equal in size to the white rhino. Fully grown males can weigh from 2200 to 3000 kilograms (4,800-6,600 pounds) and females can weigh about 1600 kilograms (3,500 pounds). The Indian rhino ranges from 1.7 to 2 meters tall (5.7-6.7 feet) and can be up to 4 meter (13 feet) long.

The single horn of the great one-horned rhinoceros curves backward from the nose and is present in both males and females, but not on newborn young. The horn, like human fingernails, is pure keratin and starts to show after about 6 years. In most adults the horn reaches a length of about 25 centimeters (9.8 inches) (Dinerstein 2003), but have been recorded up to 57.2 centimeters (22.5 inches) in length. The horn is naturally black.

Javan rhinoceros

the Javan rhinoceros (R. sondaicus).

References

ISBN links support NWE through referral fees

Lacombat, Frédéric. The evolution of the rhinoceros. In Fulconis 2005, pp. 46–49. Fulconis, R. (ed.) (2005). Save the rhinos: EAZA Rhino Campaign 2005/6. London: European Association of Zoos and Aquaria.

Dinerstein, Eric (2003), The Return of the Unicorns; The Natural History and Conservation of the Greater One-Horned Rhinoceros, New York: Columbia University Press, ISBN 0-231-08450-1

j Laurie, W.A.; E.m. Lang, and C.P. Groves (1983). Rhinoceros unicornis. Mammalian Species (211): 1–6. doi:10.2307/3504002. http://www.science.smith.edu/departments/Biology/VHAYSSEN/msi/default.html.

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