So it’s February and I need a new skull to look at – so I’ve chosen the gorilla. I have avoided doing another primate skull up to know as that is my comfort area which I studied at uni. However, I couldn’t resist any longer as I love the gorilla and have always thought of them as beautiful and majestic creatures. I also have a great interest in comparative anatomy, in particular with humans and their primate relatives. I still clearly remember my seminars where we compared different types of primates and at the end of the module had to identify varies skulls using the facts and techniques we had learnt. These were some of my favourite classes and hopefully I’ll be able to expand on this a little as the month goes on.
The gorilla (Gorilla gorilla) lives in Central Africa in forests and included two sub groups – the western lowland gorilla and the eastern lowland gorilla, the eastern is a little bigger of the two. The skull of a gorilla is fairly easy to distinguish due to it’s size and by some of the bony structures used for muscle attachment. However, the skull is easily identifiable as a primate because of it’s forward facing eyes, number of teeth and over shape of the skull.
When comparing a gorilla skull to a humans it is easy to see that the gorilla has larger brow ridges, a projecting face and an overall more robust skull. As mentioned the gorilla has many sites for large muscle attachments with a particularly distinct sagittal crest. This is located on the top of the cranium and is where the muscles for mastication (chewing) attach. These are much larger than a humans due to the type of foot the gorilla consumes. Their diet is quite varied from fruits and leaves to ants and termites. However, due to the large amount of roughage that they eat large, flat teeth and a strong jaw is needed, hence the sagittal crest.
The position of the foramen magnum is also different compared to a humans. In a gorilla this is situated further back in the skull and is related to their posture when moving. Gorillas are knuckle walkers and therefore use all four limbs to move about which results in a different posture and postion compared to humans who walk on two legs. For more information on this and other adaptations of the skeleton relating to bipedalism and location visit my first ‘skull of the month’ page on humans.
One of the easiest ways to spot a primate skull is to examine the dentition. All primates have a similar dentition pattern although this differs between families. The apes, which include humans and gorillas, have a dental formula of 18.104.22.168 which translates as two incisors, one canine, two pre-molars and three molars on each side of the mouth. This is repeated in both the upper and lower jaw. Although we have the same dental formula there are obvious differences. As mentioned gorillas eat much harder food substances and therefore have larger molars. They also have larger incisors (see image) which assist with stripping and tearing fruit but also are used for display and threat purposes. Gorillas are a sexually dimorphic species (a notable size difference between males and females) and therefore males will use their teeth to display to attract females and to appear aggressive to frighten off other males.
For an article investigating the insights into hominid evolution from the gorilla genome sequence visit my post which contains the abstract, citation and link to the full article. Also go to my page to find out a bit more about the foot of the gorilla and it’s morphology.