Physical characteristics

Hominoids share truncal erectness, for posture more than for locomotion, that seems to have evolved for climbing and sitting or hanging to feed, with their very long and mobile arms. The thorax is dorso-ventrally (antero-posteriorly) compressed, so that the scapula is dorsal and the shoulder joint projects laterally; hence, the great mobility in all directions, especially in the upper cone. The myth that all hominoids evolved from a brachiating ancestor has finally been put to rest. What the hominoids share is the ability to climb, pulling up with the strong and mobile arms, rather than the "rear-wheel drive" of monkeys that use their better developed legs.

Gibbons occupy a niche where suspensory behavior of all kinds, and the related functional anatomy, are of paramount

A siamang (Symphalangus syndactylus) calling. (Photo by R. Van Nostrand/Photo Researchers, Inc. Reproduced by permission.)

melodic, with long pure notes rising and falling during the great call.

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