Synapsida: More on Morphology

The skull depicted at the top of this page belonged to one of the dominant predators of the late Permian (about 260 million years ago), a gorgonopsid called Lycaenops. At the bottom of this page is the skull of a Pleistocene wolf. Both of them show the feature seen in all synapsids: one opening in the dermal bones of the skull. In most vertebrates, the powerful muscles that close the jaw attach to the top of the skull and must pass through a space in the bones of the skull to reach the jaw. Synapsids have one such space; diapsids have two. You can feel how your own chewing muscles pass through a space in your skull (the temporal opening) by placing your hand against the side of your face and biting down. The chewing muscles pass underneath a bony bridge (the zygomatic arch), which is found in all mammals and in their extinct relatives in the Synapsida.