Functional morphology of the palato-maxillary apparatus in "Palatine dragging" snakes (Serpentes: Elapidae: Acanthophis, Oxyuranus).

Elapid snakes have previously been divided into two groups (palatine erectors and palatine draggers) based on the morphology and inferred movements of their palatine bone during prey transport (swallowing). We investigated the morphology and the functioning of the feeding apparatus of several palatine draggers (Acanthophis antarcticus, Oxyuranus scutellatus, Pseudechis australis) and compared them to published records of palatine erectors. We found that the palatine in draggers does not move as a straight extension of the pterygoid as originally proposed. The dragger palato-pterygoid joint flexes laterally with maxillary rotation when the mouth opens and the jaw apparatus is protracted and slightly ventrally during mouth closing. In contrast, in palatine erectors, the palato-pterygoid joint flexes ventrally during upper jaw protraction. In draggers, the anterior end of the palatine also projects rostrally during protraction, unlike the stability of the anterior end seen in erectors. Palatine draggers differ from palatine erectors in four structural features of the palatine and its relationships to surrounding elements. The function of the palato-pterygoid bar in both draggers and erectors can be explained by a typical colubroid muscle contraction pattern, which acts on a set of core characters shared among all derived snakes. Although palatine dragging elapids share a fundamental design of the palato-maxillary apparatus with all higher snakes, they provide yet another demonstration of minor structural modifications producing functional variants.