Cranial Bones in Carnivorous Reptiles

Diapsid skulls

• Most reptiles, with the exception of the turtle, have a diapsid skull, which translates from the Greek to mean "two arches." There are two characteristic openings on either side of the skull known as temporal fossae. The temporal openings ensure a reduction in the weight of the cranial bones and as a result the whole skull is lighter, enabling it to have increased mobility. In the case of snakes, cranial bones do not fuse together but are instead loosely attached by ligaments to allow for movement.

Snake

• The snake is a carnivorous reptile with a skull that has evolved to have a minimum number of cranial bones to ensure maximum mobility and flexibility. The snake skull also has kinetic joints that allow movement and rotation of certain points in the cranial bones. The cranial bones in a snake include the frontal, prefrontal, parietal and nasal bones. The quadrate bone is linked to the rear mandible and supratemporal cranial bones by means of a joint that enables lateral and vertical movement and allows for the mouth to be opened very wide. The joint between the rear mandible and dental bones enables more lateral movement. This is useful when the snake is swallowing prey as it allows the snake to gulp down prey that is many times bigger than the diameter of its skull.

Crocodile

• The superior cranial bones of the crocodile have deep pits. At the time that baby crocodiles emerge from their eggs, their cranial bones have already hardened or ossified. The frontal and parietal bones of the crocodile's cranium are solidly fused together as well. But even though they have fused, they still continue to grow throughout the crocodile's life. This early solid cranium affords the crocodile protection for its brain. One of the cranial characteristics that is used to define the family Crocodilia is the fact that the quadrate bone is fixed and there is a distinct transverse bone.

Snapping Turtle

• The snapping turtle feeds on carrion, small birds and fish and this carnivore's head is too big for it to be withdrawn into its shell. The skull is anapsid which refers to the fact that the cranium is solid and unlike other carnivorous reptiles has no holes or fossae near the temples. The skull of the turtle is regarded as primitive because it has not evolved much and looks very much like the skulls of fossil turtles. The cranial bones include the parietal, supraoccipital, zygomatic or jugal and quadratojugal.