Hylobatidaegibbons and lesser apes

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This family contains 1 genus, Hylobates, and approximately 11 species (some authorities recognize a second genus, Symphalangus) . They are found only in the tropical forests of southeastern Asia, including on Sumatra, Borneo, Java, and other islands as well as the mainland. These apes are of medium size (3.9-12.7 kg). They lack tails. Their forearms are remarkably long, and both forefeet and hindfeet are long and thin. The forefeet have a deep cleft between first and second digits. The pelage of these apes is usually black, gray, or brownish, often with white markings on hands, feet, and facial region. Ischial callosities are present. Some gibbons and siamangs 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, equalling the size of the animal's head.

The skulls of hylobatids resemble those of hominids, with very short rostra, enlarged braincases, and large orbits that face forward.

Hylobatds are catarrhine primates; that is, their nostrils are close together and face forward and slightly downward. They lack cheek pouches and their stomach is not sacculated. Their teeth are similar to those of hominids. The molars are bunodont and lack lophs. The upper molars usually have a cingulum, which is sometimes large. The canines are prominent (more so than in most hominids) but not sexually dimorphic. The dental formula is 2/2, 1/1, 2/2, 3/3 = 32.

Gibbons and siamangs are monogamous, living in small family troops of usually 2-6 related individuals. These groups are territorial, maintaining their territories partly by conspicuous vocalization, which may involve loud duetting by group members. They are primarily vegetarian, feeding on figs and other fruit, leaves and shoots. They are remarkably active and agile brachiators, capable of exceeding 3m in a swing. Gibbons leap from branch to branch, sometimes travelling more than 9 m in a single leap. They also sometimes walk on large branches or on ground, assuming a bipedal stance with their arms raised for balance. Gibbons are active during the day.

Fossil hylobatids are known from the Miocene.

Technical characters

Literature and references cited

Feldhamer, G. A., L. C. Drickamer, S. H. Vessey, and J. F. Merritt. 1999. Mammalogy. Adaptation, Diversity, and Ecology. WCB McGraw-Hill, Boston. xii+563pp.

Groves, C. P. 1989. A Theory of Human and Primate Evolution. Oxford Science Publications, Clarendon Press, Oxford. xii+375 pp.

Nowak, R.M. and J.L. Paradiso. 1983. Walker's Mammals of the World, Fourth edition. John Hopkins University Press, Baltimore, London.

Szalay, F. S., and E. Dodson. 1979. Evolutionary History of the Primates. Academic Press, New York. xiv+580 pp.

Thorington, R. W., Jr., and S. Anderson. 1984. Primates. Pp. 187-216 in Anderson, S. and J. K. Jones, Jr. (eds). Orders and Families of Recent Mammals of the World. John Wiley and Sons, N.Y. xii+686 pp.

Vaughan, T. A., J. M. Ryan, N. J. Czaplewski. 2000. Mammalogy. Fourth Edition. Saunders College Publishing, Philadelphia. vii+565pp.

Wilson, D. E., and D. M. Reeder. 1993. Mammal Species of the World, A Taxonomic and Geographic Reference. 2nd edition. Smithsonian Institution Press, Washington. xviii+1206 pp.

Contributors

Phil Myers (author), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

motile

having the capacity to move from one place to another.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate