Jaw Muscles — the Therocephalian Solution
The solution came in two parts. First, a new emphasis on the muscles inside the mouth (red) through their forward expansion. Second, the fenestra was expanded upward,
forming a distinct 'sagittal crest' that provided added attachment area for the jaw-closing temporal muscles.
As with the gorgonopsids , a segment of those jaw-closing muscles
( medium blue ) attached to the outside of the
lower jaw. The primary function of this outside segment (lighter blue) was to ensure that the jaw stayed hinged – vital when seizing large, struggling prey.
However, this segment of jaw muscle was also a limiting factor, determining the therocephalian method of feeding.
The mechanics of the therocephalian jaw hinge prevented them from using the sliding gorgonopsid-style nip-and-swallow technique. Instead, big therocephalians simply sank their front teeth into
their kill, twisted their heads back and forth, while yanking away until a swallowable mouthful of flesh was torn free. Crude but it obviously worked. Canines would be too vulnerable to damage to
play a role.