35 mm slide; color. Scientific Classification: Kingdom: Animalia; Phylum: Chordata; Class: Mammalia; Order: Primates; Family: Pongidae; Genus: Gorilla; Genus species: Gorilla gorilla. Animal characteristics: Height: 1.4-1.8 m; Weight: 90-180 kg; Identification: The Western lowland gorilla has a dark black coat; adult males have a silver saddle on their back; Habitat: Tropical forests; Diet: Herbivore: foliferous - leaves and stems; Reproduction: Gorillas have no distinct breeding season. After a gestation period of 8-9 months, the female gives birth to one, rarely two, offspring. The young are weaned by three years of age. Gorillas have been known to live to almost 40 years old; Social Structure: Gorillas have the most stable social groups of any of the great apes. Group sizes can vary from 2-35 individuals. Members of a group may travel together for years at a time. Because they are too large and slow for territorial defense, groups' home ranges often overlap. Once they reach puberty, young females leave their family group to join another. Therefore, most of the females within a group are unrelated and are not closely bonded to each other. It is the dominant male's (known as a silverback) ties with the females in his group that hold the group together; Behavior: Most of a gorilla's time is spent on the ground, although they will forage and sleep in the trees. Younger animals may swing through the trees by their arms, known as brachiation. Aggression is rare, occurring only when silverbacks meet and are competing for females; Status: Endangered: habitat loss, hunted for their skulls, skins, or to be sold to zoos; Interesting Facts: Gorillas are the most sexually dimorphic of all primate species, with the males being twice as large as the females. In 1972, a female gorilla named Koko was taught sign language and now knows several hundred signs.