Closure of neurocentral sutures during crocodilian ontogeny: Implications for maturity assessment in fossil archosaurs

Abstract

Closure of neurocentral sutures in the crocodylian vertebral column follows a distinct caudal to cranial sequence during ontogeny. The sutures in most caudal vertebrae are fully closed at hatching, but closure of remaining sutures occurs later in ontogeny. Closure of cervical sutures is a consistent indicator of morphological maturity in Alligator mississippiensis, Alligator sinensis, Osteolaemus tetraspis, and Crocodylus acutus; the final transformation is the closure of the axial neurocentral suture, which occurs after the closure of the axis-odontoid suture. Because these transformations occur near the end of ontogeny in all three taxa, regardless of maximum size, closure of these sutures is a size-independent criterion of maturity; however, it is not certain if suture closure indicates the stoppage of growth. These transformations are readily identifiable in fossils, permitting the objective characterization of maturity in fossil crocodylians and possibly at least some of their closer extinct relatives.