The Skull and Head Muscles of Archosauria

Abstract

Archosaurs is the clade composed by birds (Aves) and crocodiles, alligators, and the gharial (Crocodylia). This relatedness is not obvious and for a long time was not taken into account, as birds were seen as a group separate even from the rest of reptiles. Both avians and crocodylians are morphologically very distinct and in many aspects different from each other and from the ancestral forms within Archosauria. The skulls of birds are composed of thin and light bones, many fused to each other, and others articulating in mobile joints allowing the beak to move and bend with respect to the rest of the skull. In crocodylians the skulls are massive and heavy, a solid akinetic structure built to crush prey. The accompanying muscle system, attaching onto and responsible for the movement of the head, jaws, eyes, or tongue, is equally distinct. As a result of the striking differences and the relatively recent realization of crocodylians and avians being closely related, the comparison of their anatomy has never been very straightforward. This chapter’s goal is to provide a review of archosaur anatomy and to give at least some sense of the similarities and differences between archosaur musculature.