Definitions

syndactylus

Gibbon

[gib-uhn]
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. Gibbons 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 and pair-bonded, in 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.

Depending on species and gender, gibbon's fur coloration varies from dark to light brown shades, and anywhere in between black and white. It is rare to see a completely white gibbon.

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.

The gibbons' ball-and-socket joints allow 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

Hybrids

Many gibbons are hard to identify based on fur coloration and are identified either by song or genetics. These morphological ambiguities have led to hybrids in zoos. Zoos often receive gibbons of unknown origin and therefore rely on morphological variation or labels that are impossible to verify to assign species and subspecies names so it is common for separate species of gibbons to be misidentified and housed together. Interspecific hybrids, hybrids within a genus, also occur in wild gibbons where the ranges overlap.

References

External links

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