The Indian rhinoceros (Rhinoceros unicornis), also known as the greater one-horned rhinoceros, great Indian rhinoceros, or Indian rhino for short, is a rhinoceros species native to the Indian subcontinent. It is the second largest extant species of rhinoceros, with adult males weighing 2.07–2.2 tonnes and adult females 1.6 tonnes. The skin is thick and is grey-brown in colour with pinkish skin folds. They have a single horn on their snout that grows to a maximum of 57.2 cm (22.5 in). Their upper legs and shoulders are covered in wart-like bumps, and aside from the eyelashes, ear fringes and tail brush, Indian rhinoceroses are nearly hairless.
The Indian rhinoceros is a largely solitary animal, only associating in the breeding season and when rearing calves. They are grazers, and their diet is mainly grass, but may also include twigs, leaves, branches, shrubs, flowers, fruits, and aquatic plants. Females give birth to a single calf after a gestation of 15.7 months; the birth interval is 34 to 51 months. Captive individuals can live up to 47 years. They are susceptible to diseases such as anthrax, and those caused by parasites such as leeches, ticks, and nematodes.
It is listed as Vulnerable on the IUCN Red List, as populations are fragmented and restricted to less than 20,000 km2 (7,700 sq mi). As of August 2018, the global population was estimated to comprise 3,588 individuals. Indian rhinos once ranged throughout the entire stretch of the Indo-Gangetic Plain, but excessive hunting and agricultural development reduced its range drastically to 11 sites in northern India and southern Nepal. In the early 1990s, between 1,870 and 1,895 Indian rhinos were estimated to have been alive. Since then, numbers have increased due to conservation measures taken by the government. However, poaching remains a continuous threat.
The Indian and Javan rhinoceroses, the only members of the genus Rhinoceros, first appear in the fossil record in Asia during the Early Pleistocene. The Indian rhinoceros is known from Early Pleistocene localities in Java, South China, India and Pakistan. Molecular estimates suggest the species may have diverged much earlier, around 11.7 million years ago. Although belonging to the type genus, the Indian and Javan rhinoceroses are not believed to be closely related to other rhino species. Different studies have hypothesised that they may be closely related to the extinct Gaindatherium or Punjabitherium. A detailed cladistic analysis of the Rhinocerotidae placed Rhinoceros and the extinct Punjabitherium in a clade with Dicerorhinus, the Sumatran rhinoceros. Other studies have suggested the Sumatran rhinoceros is more closely related to the two African species. The Sumatran rhino may have diverged from the other Asian rhinos as long ago as 15 million years.
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