The oldest known lepidosaur and origins of lepidosaur feeding adaptations - Nature

"Modern squamates owe their success to extraordinary adaptations in their skulls, which include extensive kinesis (Fig. 1) and the ability to flex the snout up and down (mesokinesis). Their skulls can also move the braincase relative to the cranium (metakinesis) and move the quadrate and jaw articulation (streptostyly). These combined joint movements enable lizards, especially snakes, to manipulate and swallow large prey."

"Sphenodon and fossil rhynchocephalians have largely akinetic skulls that are incapable of any movement except a small degree of metakinesis, which enables powerful bites but limited food manipulation. Modern Sphenodon and squamates differ in the presence and absence, respectively, of the lower temporal bar. In squamates, the open temporal bar is a gap between the jugal and the quadrate bones of the skull that is essential for cranial kinesis. Both Sphenodon and many squamates have extensive palatal dentition, including substantial teeth on the palatine bone."

Modern squamates exhibit extensive cranial kinesis, including mesokinesis, metakinesis, and streptostyly, allowing complex snout and braincase movements and enabling manipulation and swallowing of large prey. Sphenodon and fossil rhynchocephalians retain largely akinetic skulls with limited metakinesis, favoring powerful bites but restricting food manipulation. The presence of a lower temporal bar differs between clades, with squamates having an open temporal region that is essential for kinesis. Both Sphenodon and many squamates retain substantial palatal dentition, particularly on the palatine, which contributes to shearing, tongue-assisted processing, and prey grip in snakes. These morphological contrasts obscure ancestral lepidosaur cranial states and feeding adaptations.

Read at Nature