APE VS. HOMININ SKULLS

=Comparisons of the skull= [image:http://i.imgur.com/9nzQSqU.png] '''Cranial Capacity''': Hominins have a larger cranial capacity (apes have a cranial capacity of approx '''400cm^3^''' compared with '''1400cm^3^''' in humans). This is an indication of their brain size. '''Prognathism''': Apes have a pronounced muzzle, the teeth protrude out from their face. This is called a prognathism. This is common in early Hominins also, but later Hominins have a much flatter face. [image:http://i.imgur.com/AMSsd48.png?1] '''Foramen Magnum''' This is the hole at the base of the skull where the spinal cord enters the brain. The foramen magnum is towards the back of the skull in apes, whose posture was not fully upright. In humans, the foramen magnum is at the '''fulcrum''' (balance point). The bones of the skull that balance on the vertebra / spine, called '''occipital condyles''' show the same trend (at the rear of the skull in apes, central in humans) [image:http://i.imgur.com/LoxcaCC.png?1] '''Nuchal Area''' This is the area where the neck muscles attach onto the back of the skull, to keep it balanced on the spinal column / looking forward. Apes have very large nuchal areas and associated neck muscles because greater muscle strength is required keep the skull looking forward when the spine is attached further to the rear of the skull. [image:http://i.imgur.com/EmfdQ8q.png?2] '''Temporal muscles''' These are the muscles that pull up the jaw (bite). The temporal area is where these muscles attach onto the skull. In apes these are both much larger. This probably corresponded to a much more primitive diet that included a lot more fibrous plant material that needed to be ground down. [image:http://i.imgur.com/9OtEa3x.png?1] '''Zygomatic Arch''' These are a bony arch just behind the cheeks. They provide a gap for the temporal muscles to pass through (see above). They are much larger in apes to accommodate much larger temporal muscles. [image:http://i.imgur.com/62POzvL.png?1] '''Brow Ridge''' This is a bony ridge located above the eye sockets. Its purpose is to reinforce the weaker bones of the face (reduces vertical stress). In Apes they are much larger due to the tremendous strain put on the cranium by their temporal (jaw) muscles. Without this reinforcement the eye sockets would collapse. The brow ridge was one of the last traits to be lost in the path to modern humans [image:http://i.imgur.com/wWpWE1M.png?1] '''Sagittal Crest''' The Sagittal Crest is a ridge of bone running lengthwise along the midline of the top of the skull. The presence of this ridge of bone indicates that there are exceptionally strong jaw muscles. The sagittal crest serves primarily for attachment of the temporalis muscle, which is one of the main chewing muscles. It is absent or greatly reduced in most Hominins (with the notable exception of the Paranthropus genus). =Summary of the differences in the skull= [image:http://i.imgur.com/bJEmu42l.png] =Comparison of teeth & jaws= [image:http://i.imgur.com/WMlOzOc.png?1] '''Mandible (lower jaw)''' The mandible is much larger in apes. This is associated with a more primitive diet consisting of leaves and fibrous plants that need to be ground down. In humans a chin has developed to protect a weak point in our less robust skulls. [image:http://i.imgur.com/8KzixLy.png?1] '''Dental Arcade (upper jaw)''' The dental arcade is the shape made by the rows of teeth in the upper jaw. Apes have a much more '''U''' shaped dental arcade while humans have more '''V''' shaped dental arcade. '''Diastema''' Apes have a gap known as the diastema between the upper incisors and canines. This gap accommodates the enlarged lower canines. Canines are generally much larger in males (sexual dimorphism) suggesting that they primarily used for dominance displays between males competing for females. [image:http://i.imgur.com/wYmYix3l.png?1] '''Teeth''' Apes have much '''larger canines''' and '''incisors'''. While some apes do eat meat their diet is predominantly vegetarian and these teeth may have played a more significant role in defence. Apes also have a much '''larger grinding surface on their molars''' to process leafy and fibrous plant material.In humans the canines are roughly the same size in the two sexes. In many apes the canines are considerably larger in males than females. As the males compete for females, larger canines are selected for. The teeth of apes tend to have thinner enamel, an adaption to eating fruit. Human teeth have thick enamel, an adaption for chewing tougher food.