An upper Cretaceous lizard with a lower temporal arcade.

The reduced lower temporal arcade of the skull and the movable quadrate are the most distinctive features of squamates. Up to now, no exception has been documented for any fossil or extant squamates. We report here a new fossil lizard that possesses a complete lower temporal arcade and an unmovable quadrate. The anatomical relationships indicate that those two modifications were secondarily obtained in the new lizard. The complete lower temporal bar and the firm contact between the pterygoid and quadrate may have served as a brace to support the quadrate jaw articulation and thus prevent it from twisting anteriorly rather than posteriorly during the bite cycles. This represents an entirely new pattern of jaw muscle functions within the Squamata.