STATIC BITING IN LIZARDS - FUNCTIONAL-MORPHOLOGY OF THE TEMPORAL LIGAMENTS

In lizards, the basic lepidosaurian bauplan of the skull is modified b y the reduction of one or more skull elements such as the lower tempor al bar (e.g. iguanids), the upper temporal bar (e.g. varanids) and the postorbital bar (e.g. geckos). Skull modifications in Plocederma stel lio, Uromastix acanthinurus, Corucia zebrata and Tiliqua scincoides ar e restricted to the reduction of the lower temporal arcade (the plesio morph condition for lizards; i.e. possessing a 'basic' skull). In spit e of the potential mobility (streptostyly) of the quadrate, none of th ese species shows streptostylic movements during the static power phas e of biting. It is assumed that the temporal ligaments fulfil the role of the lower temporal arcade in stabilizing the quadrate. This functi on is supported by the results of mathematical simulations, which demo nstrate that static biting loads the ligament in tension. Apparently, these basic lizard skulls show a shift of the attachment site of the t emporal ligament from the quadrate ro the lower jaw. This does not aff ect its quadrate-stabilizing function. However, analyses of forces occ urring in the quadratomandibular joint suggest that skull configuratio ns with a jugomandibular ligament confine the possible orientations of the joint forces to a narrow range, more aligned with the quadrate. I n this way, optimization of the joint morphology to resist loads impos ed by biting might more easily be reached. This is assumed to be impor tant for lizards with a robust skull built for forceful biting.