Gibbon

Gibbons are the small apes in the family Hylobatidae. The family is divided into four genera based on their diploid chromosome number: Hylobates (44), Hoolock (38), Nomascus (52), and Symphalangus (50). The extinct Bunopithecus sericus is a gibbon or gibbon-like ape which, until recently, was thought to be closely related to the Hoolock gibbons. . They occur in tropical and subtropical rainforests from northeast India to Indonesia and north to southern China, including the islands of Sumatra, Borneo and Java.

Also called the lesser apes, gibbons differ from great apes (chimpanzees, gorillas, orangutans and humans) in being smaller, pair-bonded, not making nests, and in certain anatomical details in which they superficially more closely resemble monkeys than great apes do. Gibbons are masters of their primary mode of locomotion, brachiation, swinging from branch to branch distances of up to 15 m (50 ft), at speeds as much as 56 km/h (35 mph). They can also make leaps of up to 8 m (27 ft), and walk bipedally with their arms raised for balance. They are the fastest and most agile of all tree-dwelling, non-flying mammals.

Anatomy
One unique aspect of gibbon physiology is that the wrist is composed of a ball and socket joint, allowing for biaxial movement. This greatly reduces the amount of energy needed in the upper arm and torso, while also reducing stress on the shoulder joint. They also have long hands and feet, with a deep cleft between the first and second digits of their hands. Their fur is usually black, gray, or brownish, often with white markings on hands, feet, and face. Some species have an enlarged throat sac, which inflates and serves as a resonating chamber when the animals call. This structure is enormous in a few species, equaling the size of the animal's head.

Gibbon skulls resemble those of great apes, with very short rostra, enlarged braincases, and large orbits that face forward. Gibbons have the typical nose of catarrhine primates with nostrils that are close together and face forward and slightly downward. They lack cheek pouches and their stomach is not sacculated. Their teeth also are similar to the great apes, with molars that are bunodont and lack lophs. The upper molars usually have a cingulum, which is sometimes large. The canines are prominent but not sexually dimorphic. The dental formula is:

Behavior
Gibbons are social animals. They are strongly territorial, and defend their boundaries with vigorous visual and vocal displays. The vocal element, which can often be heard for distances of up to 1 km, consists of a duet between a mated pair, their young sometimes joining in. In most species, males, and in some also females, sing solos that attract mates as well as advertise their territory. The songs can make them an easy find for poachers who engage in the illegal wildlife trade and in sales of body parts for use in traditional medicine.

Unlike any other primate, gibbons have a ball-and-socket joint in each wrist, allowing them unmatched speed and accuracy when swinging through trees. Nonetheless, their mode of transportation can lead to hazards when a branch breaks or a hand slips, and researchers estimate that the majority of Gibbons fracture their bones one or more times during their lifetimes.

Status
Most species are threatened or endangered, most importantly from degradation or loss of their forest habitat. Gibbon species include the Siamang, the White-handed or Lar Gibbon, and the hoolock gibbons. The Siamang, which is the largest of the 13 species, is distinguished by having two fingers on each hand stuck together, hence the generic and species names Symphalangus and syndactylus.

Classification

 * Family Hylobatidae: gibbons
 * Genus Hylobates
 * Lar Gibbon or White-handed Gibbon, Hylobates lar
 * Malaysian Lar Gibbon, Hylobates lar lar
 * Carpenter's Lar Gibbon, Hylobates lar carpenteri
 * Central Lar Gibbon, Hylobates lar entelloides
 * Sumatran Lar Gibbon, Hylobates lar vestitus
 * Yunnan Lar Gibbon, Hylobates lar yunnanensis
 * Agile Gibbon or Black-handed Gibbon, Hylobates agilis
 * Mountain Agile Gibbon, Hylobates agilis agilis
 * Bornean White-bearded Gibbon, Hylobates agilis albibarbis
 * Lowland Agile Gibbon, Hylobates agilis unko
 * Müller's Bornean Gibbon, Hylobates muelleri
 * Müller's Gray Gibbon, Hylobates muelleri muelleri
 * Abbott's Gray Gibbon, Hylobates muelleri abbotti
 * Northern Gray Gibbon, Hylobates muelleri funereus
 * Silvery Gibbon, Hylobates moloch
 * Western Silvery Gibbon or Western Javan Gibbon, Hylobates moloch moloch
 * Eastern Silvery Gibbon or Central Javan Gibbon, Hylobates moloch pongoalsoni
 * Pileated Gibbon or Capped Gibbon, Hylobates pileatus
 * Kloss's Gibbon or Mentawai Gibbon or Bilou, Hylobates klossii
 * Genus Hoolock
 * Western Hoolock Gibbon, Hoolock hoolock
 * Eastern Hoolock Gibbon, Hoolock leuconedys
 * Genus Symphalangus
 * Siamang, Symphalangus syndactylus
 * Genus Nomascus
 * Concolor or Black Crested Gibbon, Nomascus concolor
 * Nomascus concolor concolor
 * Nomascus concolor lu
 * Nomascus concolor jingdongensis
 * Nomascus concolor furvogaster
 * Eastern Black Crested Gibbon, Nomascus nasutus
 * Cao Vit Gibbon, Nomascus nasutus nasutus
 * Hainan Gibbon, Nomascus nasutus hainanus
 * White-cheeked Crested Gibbon, Nomascus leucogenys
 * Northern White-cheeked Crested Gibbon, Nomascus leucogenys leucogenys
 * Southern White-cheeked Crested Gibbon, Nomascus leucogenys siki
 * Yellow-cheeked Gibbon, Nomascus gabriellae