The Javan rhinoceros (Rhinoceros sondaicus), also called Javan rhino, Sunda rhinoceros and lesser one-horned rhinoceros is a critically endangered member of the genus Rhinoceros of the family Rhinocerotidae, and one of the five remaining extant rhinoceros species. It has a plate-like skin with protective folds and is one of the smallest rhinoceros species with a body length of 3.1–3.2 m (10.2–10.5 ft) and a 1.4–1.7 m (4.6–5.6 ft) long tail. The heaviest specimens weigh around 2,300 kg (5,100 lb). Its horn is usually shorter than 25 cm (9.8 in). Until the mid-19th to about the early 20th century, the Javan rhinoceros had ranged beyond the islands of Java and Sumatra and onto the mainland of Southeast Asia and Indochina, northwest into East India, Bhutan, and the south of China. Today, it is the rarest of all rhinoceroses, and among the rarest of all living animal species, with only one currently known wild population, and no individuals successfully kept in captivity. It is among the rarest large mammals in the world with a population around 74 within Ujung Kulon National Park, at the far western tip of Java, Indonesia. The decline of the Javan rhinoceros is primarily attributed to poaching for the males' horns, which are highly valued in traditional Chinese medicine, fetching as much as US$30,000 per kg on the black market. As the presence of colonial Dutch and other Europeans in its range increased, peaking in the 1700–1800s, trophy hunting also became a serious threat. Loss of habitat and massive human population growth especially postwar times have also contributed to its decline and hindered the species' recovery. The remaining range is within one nationally protected area, and Ujung Kulon is also a UNESCO World Heritage Site. Nonetheless, rural, potentially rugged park boundaries mean that law enforcement cannot be equally present in all places at all times; in some areas, this lack of security still places the species at risk from poachers, disease exposure, and ultimately loss of genetic diversity, leading to genetic "bottlenecking" (i.e., inbreeding depression). The Javan rhinoceros can live around 30–45 years in the wild. It historically inhabited dense lowland rainforest, wet grasslands, and vast floodplains at forest edges. It is mostly solitary, except for courtship and rearing offspring, though groups may occasionally congregate near wallows and salt licks. Aside from humans, whom they usually avoid, adults have no natural predators in their range. Very small juveniles may be preyed upon, if left unsupervised, typically by Javan leopards, the now extinct Javan tiger, or rarely saltwater crocodiles. Scientists and conservationists rarely study the animals directly due to their extreme rarity and the danger of interfering with such an endangered species. Researchers instead rely on camera traps and fecal samples to gauge health and behavior. Consequently, Javan rhinos are the least-studied of all rhinoceros species. Two adult female Javan rhinoceroses, each with a calf, were filmed using a motion-triggered trail camera, the video being released on 28 February 2011 by WWF and Indonesia's National Park Authority, proving they are still breeding in the wild.
Etymology The generic name Rhinoceros is a combination of the ancient Greek words ῥίς (ris) meaning nose and κέρας (keras) meaning horn of an animal. The specific name sondaicus is derived from sunda, the biogeographical region that comprises the islands of Sumatra, Java, Borneo, and surrounding smaller islands. The Javan rhino is also known as the lesser one-horned rhinoceros (in contrast with the greater one-horned rhinoceros, another name for the Indian rhino).
Taxonomy Rhinoceros sondaicus was the scientific name used by Anselme Gaëtan Desmarest in 1822 for a rhinoceros from Java sent by Pierre-Médard Diard and Alfred Duvaucel to the National Museum of Natural History, France. In the 19th century, several zoological specimens of hornless rhinoceroses were described:
Rhinoceros inermis proposed by René Lesson in 1838 was a female rhinoceros without horns shot in the Sundarbans. Rhinoceros nasalis and Rhinoceros floweri proposed by John Edward Gray in 1867 were two rhinoceros skulls from Borneo and one from Sumatra, respectively. Rhinoceros annamiticus proposed by Pierre Marie Heude in 1892 was a specimen from Vietnam. As of 2005, three Javan rhinoceros subspecies are considered valid taxa:
R. s. sondaicus, the nominate subspecies, known as the Indonesian Javan rhinoceros R. s. inermis, known as the Indian Javan rhinoceros or lesser Indian rhinoceros R. s. annamiticus, known as the Vietnamese Javan rhinoceros or Vietnamese rhinoceros
Evolution
Ancestral rhinoceroses are held to have first diverged from other perissodactyls in the Early Eocene. Mitochondrial DNA comparison suggests the ancestors of modern rhinos split from the ancestors of the Equidae around 50 million years ago (Mya). The extant family, the Rhinocerotidae, first appeared in the Late Eocene in Eurasia, and the ancestors of the extant rhino species dispersed from Asia beginning in the Miocene. The last common ancestor of living rhinoceroses belonging to the subfamily Rhinocerotinae is suggested to have lived around 16 Mya, with the ancestors of the genus Rhinoceros diverging from the ancestors of other living rhinoceroses around 15 Mya. The genus Rhinoceros has been found to be overall slightly more closely related to the Sumatran rhinoceros (as well as to the extinct woolly rhinoceros and the extinct Eurasian genus Stephanorhinus) than to living African rhinoceroses, though gene flow appears to have occurred between the ancestors of living African rhinoceroses and the genus Rhinoceros, as well as between the ancestors of the genus Rhinoceros and the ancestors of the woolly rhinoceros and Stephanorhinus. A cladogram showing the relationships of recent and Late Pleistocene rhinoceros species (minus Stephanorhinus hemitoechus) based on whole nuclear genomes
The oldest known definitive fossils of the Javan rhinoceros are from the Late Pliocene deposits of Myanmar, Java, and Pakistan. Molecular estimates suggest the Indian and Javan rhinoceros diverged from each other earlier, around 4.3 million years ago. An astragalus fossil similar to that of the Javan rhinoceros from the Late Miocene deposits of Myanmar have been identified as Rhinoceros cf. R. sondaicus.
Description
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