Gibbons, specifically the Siamang (Symphalangus syndactylus), are a robustly built species among the 10 other species in the family Hylobatidae. Measuring 75-90 cm (29.5-35.4 in) long and weighing 8-13 kg (17.6-28.6 lbs), S. syndactylus possesses an arm-spread of 1.5 m (almost 5 ft). S. syndactylus is black in color with a longer, thinner coat than other species. The Siamang is distinguished by a large, hairless, empty air sac on the front of their throats that inflates during vocalization, and by webbing between their second and third toes. S.
Orangutans belong to a single species known as Pongo pygmaeus categorized into two subspecies: P. p. pygmaeus of Borneo, and P. p. abelii of Sumatra. Orangutans have specialized upper limbs adapted for suspensory locomotion but are quadrupeds when on the ground. Standing 1.25-1.5 m (4 - 5 ft) tall, Orangutans have an arm span of about 2.25 m (7.4 ft). Adult males weigh 50-90 kg (110 - 198 lbs) and adult females 30-50 kg (66 - 110 lbs). They have bulging foreheads, protruding snouts, thin lips, and small ears.