The cervical musculature in helodermatid lizards

The evolution of an independently moveable craniocervical system is a key feature in the evolution of amniote organisms. The cervical system not only plays a crucial role during the orientation of the head towards external stimuli (e.g. visual, auditive stimuli), but is also of major importance during the inertial components of feeding in amniotes. Although the cervical system and its musculature are generally well studied in mammals, archosaurs (birds and crocodiles) and turtles, very little is known about the cervical system in some of the most primitive amniotes (lepidosaurians). In a first step towards elucidating the evolution of the cervical system, we examined the neck musculature in lizards of the family Helodermatidae. Tn general, the bauplan of the cervical muscular system appears stable within closely related phylogenetic groups. Nevertheless, preliminary data suggest that the evolutionary shift from a lingual-based to a predominantly inertial feeding system within lizards coincides with an increase in the complexity of mainly the epaxial components of the cervical musculature. A ``new'' comprehensive nomenclature of lizard neck muscles (based on the work of NISI, 1916) is proposed, and should enable future workers to interprete the neck musculature in an evolutionary context.