The Jaw Apparatus of Lialis (Lacertilia, Pygopodidae): Patterns of Intensification of Cranial Kinesis and the Problem of the Origin of Snakes

摘要

The pygopod Lialis has the most strongly developed cranial kinesis of all lizards examined. The intensification of cranial kinesis in Lialis was morphologically based on alterations in the positions of the palatal arches and basipterygoid processes, so that the palate changed the direction of movements. This significantly increased the range of movement of the cranial mechanism Lialis retains an amphikinetic skull and a jaw muscle construction that is characteristic of all Gekkota lizards. In the course of snake evolution, conversely, cranial kinesis was intensified through profound changes in the cranial structure (substitution of amphikinesis by prokinesis) and jaw musculature. These differences were probably the result of different initial designs in the jaw apparatus of the ancestors of pygopodids and snakes. The modes of function intensification in the evolution of organs are discussed.