The head and neck muscles associated with feeding in Sphenodon (Reptilia: Lepidosauria: Rhynchocephalia)

Abstract

Feeding in Sphenodon, the tuatara of New Zealand, is of interest for several reasons. First, the modern animal is threatened by extinction, and some populations are in competition for food with Pacific rats. Second, Sphenodon demonstrates a feeding apparatus that is unique to living amniotes: an enlarged palatine tooth row, acrodont dentition, enlarged incisor-like teeth on the premaxilla, a posterior extension of the dentary and an elongate articular surtace that permits prooral shearing. Third, Sphenodon has a skull with two complete lateral temporal bars and is therefore structurally analogous to the configuration hypothesised for the ancestral diapsid reptile. Furthermore, the fossil relatives of Sphenodon demonstrate considerable variation in terms of feeding apparatus and skull shape. Lastly, as Sphenodon is the only extant rhynchocephalian it represents a potentially useful reference taxon for both muscle reconstruction in extinct reptile taxa and determination of muscle homology in extant taxa. Here we provide an up-to-date consensus view of osteology and musculature in Sphenodon that is relevant to feeding. Discrepancies within previous descriptions are evaluated and synthesised with new observations. This paper displays the complex muscle arrangement using a range of different imaging techniques and a variety of different angles. This includes photographs, illustrations, schematic diagrams, and micro-computed tomography (micro-CT) slice images.