Form, function, and evolution of archosaur mandibular symphyses

Abstract

Archosaurs radiated into numerous trophic niches during their evolution, resulting in a diversity of cranial adaptations and feeding behaviors. The mandibular symphysis is a poorly understood cranial joint which may offer significant insight into cranial development and function, feeding ecology, and evolution in these vertebrates. We investigated the anatomy and evolution of archosaur symphyses with a focus on Alligator mississippiensis and crocodyliforms. Character complexes of extant and fossil species were identified and their evolution was traced using a current phylogeny of archosauriforms. During ontogeny, alligators rapidly develop a complex, interdigitated, Class III symphysis coupled with fused Meckel's cartilages. Major iterative transitions from plesiomorphic Class I to derived, rigid Class II–IV symphyses and beaks occurred along the lines to phytosaurs, aetosaurs, poposauroids, crocodyliforms, pterosaurs, ornithischians, and birds. These transitions in symphyseal morphology appear to correlate with changes in function, the origin of beaks, and potentially inferred diet.Grant Funding Source: n/a