The feeding apparatus of dyrosaurids (Crocodyliformes)

Abstract

AbstractReconstructed soft-tissues of the craniocervical region of dyrosaurids are analysed under functional aspects to determine their prey-catching capabilities. Jaw adductors and jaw abductors are enlarged and possess longer muscle fibres that are increased by a long retroarticular process. This muscle enlargement resulted in a more forceful and quicker contraction, effective for movement of the long rostrum. The occipital joint and the cervical ribs, the long retroarticular process and the high cervical neural spines of dyrosaurids suggest a higher dorsoventral flexibility of the craniocervical region, whereas lateromedial flexibility was reduced. The epaxial muscles of the neck and scapular muscles were enlarged, and the supraspinal ligament most likely fanned out into a nuchal ligament. Suspension of the neck and skull of dyrosaurids was achieved by the scapular muscles, dorsal neck ligaments and epaxial muscles, whereas ventral bracing was reduced. From the reconstructed specializations of the feeding apparatus, an enhanced capability for movements in the vertical plane is postulated for dyrosaurids, together with reduced lateral movements of the craniocervical region. Besides laterally directed strokes for fish-catching, behaviours such as poking in the substrate, bottom feeding, multidirectional prey-catching strokes and improvement of diving skills were options for dyrosaurids and suggest a possible expansion of their diet. The longirostrine skull limited prey size, but the dentition allowed shelly prey items. The specialization of the food-capturing system in dyrosaurids and the resulting expansion of their food spectrum is one possible explanation for their evolutionary success, including their undisturbed transition of the Cretaceous–Palaeogene boundary.