A Question of Species...

Eastern (Mountain) Gorilla mother with baby on backWestern (Lowland) Gorilla cradling her baby
       











The photo to the left shows a female Western Lowland Gorilla (G. gorilla) and her infant. For comparison, the photo to the right shows a female Mountain Gorilla (G. beringei) and her infant.

        Gorilla gorilla
is the smaller of the two species in the genus Gorilla. It has short hair, which is more gray than the long, black hair of Gorilla beringei. The Western Gorilla has a patch of brown hair on the tops of its head. Both species' bodies are stocky and their forearms are considerably longer than their upper arms. The hands and feet of the Western Gorilla are larger and its arms are longer than those of the eastern species. Facially the two species differ in the fact that Western Gorilla has a lower forehead, shorter palate, and slightly smaller nostrils. G. gorilla is found in areas of west-central Africa, while G. beringei is found at least 650 miles away in patches east-central Africa. 3,6,7,8  Learn more about the habitat of the Western Gorilla here.

        G. gorilla and G. beringei were not considered separate species until a few years ago. Even then, it was unknown how the two species evolved from a common ancestor. In 2007, the results of a study were revealed in which large amounts of non-coding nuclear DNA from 18 gorillas were sequenced. This led to the discovery that the two species originally separated about one million years ago, but continued to breed with each other in small amounts for at least 770,000 years, gradually moving farther apart geographically and genetically. 6

        Gorillas are sexually dimorphic. Female Western Gorillas weigh between 150 and 250 pounds; they usually measure about 5 feet tall when standing bipedally and 3.5 to 4 feet tall when standing in their normal quadrupedal position. In contrast, males stand approximately 5.5 feet tall upright and 4.5 feet tall normally, and they weigh anywhere from 300 to 500 pounds. Light, silvery hair spreads over the backs and upper thighs of males as they mature, earning them the name "silverbacks." Mature males also develop a more prominent crest down the center of their skull. 3,7,8 Learn more about the Western Gorilla's body here.

A Cross River Gorilla in the wildA Western Lowland Gorilla in a zoo



  
The photo on the left shows a Cross River Gorilla (G. g. diehli) in Cameroon, while the photo on the right shows a Western Lowland Gorilla in a zoo in the United States.  
       
        G. gorilla has two subspecies, G. g. gorilla, commonly called the Western Lowland Gorilla, and G. g. diehli, also known as the Cross River Gorilla. The latter subspecies was only very recently identified. This is due to its very limited population and habitat; only 250 to 300 individual Cross River Gorillas exist, all within an isolated area of forest spanning 290 square miles in western Cameroon and south-eastern Nigeria. Consequently, little information is yet available about G. g. diehli in comparison to G. g. gorilla, which is estimated to have a population numbering about 100,000 in the wild. (However, many serious threats are rapidly decreasing its numbers.) The two subspecies have certain  variations between their respective tooth and skull measurements, resulting in slightly different facial structures. Western Lowland Gorillas are the only members of the genus Gorilla found in U.S. zoos. 3,8

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