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There are 2 species - the Western and Eastern gorillas, and both species have silverback males. The larger of the two is the Eastern Gorilla. The maximum size of a male gorilla can be over 225 kg (500 lb) and 1.83 m (6 ft) in the wild, with much heavier weights recorded in captivity. (Although I can't find a decent reference to the recorded sizes either.)
Female gorillas are shorter with smaller arm spans. Adult male gorillas are known as silverbacks due to the characteristic silver hair on their backs reaching to the hips. Occasionally, a silverback of over 1.8 m (5 ft 11 in) and 230 kg (510 lb) has been recorded in the wild. Obese gorillas in captivity can weigh as much as 270 kg (600 lb).