Trachypithecus

Trachypithecus is a genus of Old World monkeys containing species known as lutungs, langurs, or leaf monkeys. Their range is much of Southeast Asia (northeast India, Vietnam, southern China, Borneo, Thailand, Java, and Bali).

The name "lutung" comes from the Sundanese language meaning "blackness", ultimately from Proto-Austronesian *luCuŋ (which originally referred to the Formosan rock macaque); it is preferred in one paper because the authors wanted the name langurs to only refer to monkeys in the genus Semnopithecus, although some "lutungs" are now "langurs" again. The scientific name of the genus comes from the Ancient Greek τραχύς (trakhús), meaning "rough", and πίθηκος (píthēkos), meaning "monkey".

Evolution

Genetic analysis indicates that the ancestors of the modern species of lutung first differentiated from one another a little over 3 million years ago, during the late Pliocene. The various species alive today then diverged during the Pleistocene, presumably driven by habitat changes during the Ice Ages. The oldest fossils clearly identified as belonging to the genus date from the middle Pleistocene of Vietnam and Laos; later fossils are also known from Thailand, Java, and Sumatra. The closest living relatives of the lutungs are probably either the gray langurs or the surilis, although the exact relationships remain unclear, possibly due to hybridisation between these genera during the course of their recent evolutionary history.

Taxonomy

As of 2005, the authors of Mammal Species of the World recognize the following Trachypithecus species:

• Genus Semnopithecus formerly T. vetulus group - moved into genus Semnopithecus in most recent classifications Purple-faced langur, Semnopithecus vetulus Nilgiri langur, Semnopithecus johnii
• Genus Trachypithecus T. cristatus group Javan lutung, Trachypithecus auratus "Silvery lutung", silvery langur, etc.: Trachypithecus cristatus, but also used for T. germaini Indochinese lutung or Germain's langur, Trachypithecus germaini Tenasserim lutung, Trachypithecus barbei T. obscurus group Dusky leaf monkey, Trachypithecus obscurus Phayre's leaf monkey, Trachypithecus phayrei T. pileatus group Capped langur, Trachypithecus pileatus Shortridge's langur, Trachypithecus shortridgei Gee's golden langur, Trachypithecus geei T. francoisi group Francois' langur, Trachypithecus francoisi Hatinh langur, Trachypithecus hatinhensis "White-headed langur", Trachypithecus poliocephalus Laotian langur, Trachypithecus laotum Delacour's langur, Trachypithecus delacouri Indochinese black langur, Trachypithecus ebenus

Since then, the T. vetulus group (the purple-faced langur and the Nilgiri langur) have been moved the genus Semnopithecus based on DNA and other evidence.

In 2008, Roos et al. described the Malay Peninsula form of the silvery lutung as a separate subspecies and subsequently it has been elevated to a separate species within the T. cristatus group as the Selangor silvered langur, T. selangorensis. Roos et al. also elevated the West Javan Langur, Trachypithecus mauritius, and Annamese Langur, Trachypithecus margarita, to species status (formerly subspecies of T. auratus and T. germaini, respectively). In 2020, Roos et al. discovered a new species, Popa langur (T. popa), which is found only in Myanmar. Lastly, the White-headed langur (T. leucocephalus), previously thought to be a subspecies of the Francois langur (T. Francois) or Cat Ba langur (T. poliocephalus), is currently recognized as a distinct species by IUCN Red List assessors and the American Society of Mammalogists, based on a 2007 paper by Groves.

This leaves the current understanding of the genus Trachypithecus to be:

Physical description

Lutungs have a rather slim build with a long tail. The fur color varies, depending on the species, from black and grey to orange yellow. Many species have skin designs and a brighter lower surface, the hair on the head is often compared to a hood. Their arms are very short in comparison to their hind legs, and their thumbs are also somewhat shorter than in other primates. The inner surfaces of the hands and feet are hairless so that their fur does not get caught when reaching into branches. These animals reach a length of 40 to 80 cm and a weight of 5 to 15 kg, with males being generally larger than females. A ridge over the eyes and other details, primarily related to the head, differentiate the lutungs from the surilis.

Habitat and distribution

Lutungs live in forests. They often prefer rainforests, although they are occasionally also found in secluded mountain forests and limestone karst forests. Lutungs are found in South-east Asia and parts of South Asia, from India in the west to China in the east.

Behaviour

Lutungs spend the largest part of the day in the trees, where they walk along the branches on all fours.They also jump from tree to tree, often covering long distances between trees; those long jumps are referred to as leaping. Lutungs are diurnal, although more active in the early mornings and the afternoon.

They live in groups of five to 20 animals, mostly in harems, i.e. a single male with several females. Young males must leave their birth group when fully mature, often forming bachelor groups. If a new male takes over a harem, defeating or scaring off the former harem leader, he often kills the infants in the group. This behavior is also known as infanticide. Lutungs are territorial, and emit loud calls to defend their territories from rival males, resorting to force if the outsiders are not scared off. They have a common repertoire of sounds with which they warn group members. Mutual grooming also plays an important role in maintaining the bonds between individuals.

Lutungs are herbivores, primarily eating leaves, fruits, and buds. To digest the tough leaves, they developed a multichambered stomach.

Reproduction

Lutungs typically give birth to a single young, after a seven-month gestation period. Twins occur, but are rare. Newborns usually have golden-yellow or orange fur. The mother shares responsibilities of rearing the young with the other females ("aunties") of the harem. Females within a group hand the young around, play with them, carry them, and cuddle them, allowing the mother to forage or spend time alone. If the mother dies, another female adopts the young animal. Lutungs are weaned in the latter half of their first year, and reach full maturity at 4 to 5 years. The life expectancy is estimated at 20 years.

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