First of all thanks to everyone who helped out with a few questions I had in a previous text. I recently received an email from a Primatologist who answered my questions the best she could, and I thought I'd like to share them with the rest of you. It reads as follows...
Hello Rob,
I am a primatologist, but I do not focus my studies on great apes. I study lemurs, which are prosimians, that live on the Island of Madagascar. I can answer a few of your questions, and could give you some resources to answer the ones that I cannot.
> 1. Is the conical shape of a gorillas head, caused by a saggittal formation on the skull or is it muscle?
^The answer is - BOTH! Bone is formed by its function in the body. Because gorillas have such massive jaws and the fact that they must chew so much fibrous foods, they have very strong mandibular muscles. These chewing muscles have to attach at a certain place on the skull (in humans, near the temples). The massive muscles used in chewing in gorillas creates the need for a larger place for the muscles to attach, therefore encouraging bone growth in these areas. This is also seen in early hominid ancestors such as Australopitecines. Another aspect of this large saggital crest in gorillas may be the result of sexual selection and reproduction. Perhaps female gorillas are more attracted to males with large saggital crests, and so those males get to mate more often. This would select for generation after generation of large-crested males.
> 2. Although a seemingly quiet animal, does the Gorilla have a long distance call to communicate with others of it's kind over long distances? (Howls, Roars, Moans, ect)
^This I am not 100% sure about. Gorillas are not my specialty. I know that almost all of their vocalisations are low grunts, etc. The chest-beating sound (a kind of popping noise) can be heard over long distances. Only under severe threat (usually by hunters) will gorillas become agitated enough to roar, but in this case, it is not a long-distance communication sound, but rather a warning.
> 4. Other than knuckle walking, what is the biological purpose of the elongated Ulna & Radius on Both Gorillas, and Orangutans?
^Most apes, like gorillas and orangs (along with other apes such as gibbons and siamangs) are considered to be brachiators. This is a type of locomotion involving swinging under the brances of trees, most acrobatically demonstrated by gibbons. Gorillas and orangs do not express this behaviour because of their massive body size, but if you examine a skeleton, you can see the evidence in the arms and rib cages that they are built for that activity. Once the gorillas adapted to a more terrestrial lifestyle, they developed knuckle-walking. Again, looking at a skeleton, one can see the effects of supporting that body weight on the forearms by the elongation and bowing of the raduis and ulna. Orangs actually do not knuckle-walk, and rarely locomote on the ground. They are what we call "suspensory climbers," meaning they hang under the branches and will slowly climb from tree to tree. Aided by their large size, they will actually bend small trees to swing them towards the next tree using their weight as propulsion. Their long forearms are there for brachiation, hanging and climbing.
Remember: It is difficult to think of an animals limbs as being "long" or "short" because you must compare them to the relative body size of that animal and consider its function in that animal's environment!
> 5. Herbivores have there eyes on the side of their skulls while Carnivores, and Omnivores have there eyes set to the front of their skulls. We know that Chimpanzees eat meat, and in fact (rarely) eat there own kind. In your studies have you ever heard of or know of Gorillas, or Orangutans doing the same thing? Such as hunting predatorily, for small game or fish.
^Primates have developed forward-directed eyes for binocular vision (as well as 3-D and colour vision). This allows them to focus more on the sense of sight in finding food. This does, however, reduce the range of vision (i.e. you can only see in front of you) and therefore puts you more at risk of predators.
As gorillas and orangs are not my specialisation, I am not certain how much evidence there is for meat-eating or hunting/predatory skills in either species. This also may differ by sub-specie! A colleage of mine studies feeding preference of mountain gorillas, and her study consists only of plant data.
I hope I have answered your questions, and not made things too confusing. If you are interested in the studies that have been done on gorillas and orangutans, the classic studies of gorillas have been done by George Schaller and later, Dian Fossey. Also A.H. Harcourt and A. Plumptree. Orang studies were pioneered by Birute Galdikas, who is still working in the field.
If you come up with any other questions, I would be happy to try to answer them.
Cheers,
Christina
Posted on Feb 19, 2002, 4:27 PM from IP address 198.81.17.177