Cranial Kinesis in Lepidosaurs: Skulls in Motion

This chapter reviews various aspects of cranial kinesis, or the presence of moveable joints within the cranium, with a concentration on lepidosaurs. Previous studies tend to focus on morphological correlates of cranial kinesis, without taking into account experimental evidence supporting or refuting the presence of the various forms of cranial kinesis in these taxa. By reviewing experimental and anatomical evidence, the validity of putative functional hypotheses for cranial kinesis in lepidosaurs is addressed. These data are also considered with respect to phylogeny, as such an approach is potentially revealing regarding the development of various forms of cranial kinesis from an evolutionary perspective. While existing evidence does not allow for events leading to the origin of cranial kinesis in lepidosaurs to be clearly understood at the present time, the potential role of exaptation in its development for specific groups (i.e., cordylids, gekkonids, varanids) is considered here. Directions for further research include greater understanding of the distribution of cranial kinesis in lepidosaurs, investigation of intraspecific variation of this feature (with a focus on ontogenetic factors and prey properties as variables which may influence the presence of kinesis), and continued study of the relationship between experimentally proven observation of cranial kinesis and cranial morphology. Key words: cranial kinesis, lepidosaur skull, functional morphology