Sequence of neurocentral closure in Bonitasaura salgadoi (Sauropoda: Titanosauria)


Closure of osseous sutures is used as relative maturity indicators as it mostly occurs in late juvenile stages along vertebrate ontogeny. Although there is not a strict spatial/temporal sequence of suture fusions, general patterns can be recognized in certain skeletal areas of different groups. One of these cases is the neurocentral closure between the vertebral centrum and neural arch. In living vertebrates the closure sequence can be observed by the study of specimens in different ontogenetic stages. In crocodyliforms, for example, it can be recognized a posterior-anterior neurocentral closure, while in birds the sequence appears to run in the opposite direction. On the other hand, in the still poorly analyzed case of non-avian dinosaurs,
different models are present. In Sauropoda, only the sequence of closure of Camarasaurus Cope was studied in detail. The remains of Bonitasaura salgadoi Apesteguía include several cervical, dorsal and caudal vertebrae with evident osseous sutures between vertebral components. Three levels of fusion can be discriminate: free centra and neural arches with rugose contact surfaces, partially fused vertebrae with subtle sutures, and completely fused pieces with almost no sutures. Despite only one specimen was found, the sequence of closure can be described as follows: 1) neurocentral fusion of axis; 2) neurocentral fusion of caudal vertebrae in posterior-anterior direction; 3) simultaneous fusion of dorsal and cervical vertebrae in posterior-anterior direction. This unordered temporal sequence of closure, also recorded in Camarasaurus, is unique within dinosaurs perhaps showing the presence of heterochronic processes in macronarian evolution.

(1) Área de Paleontología, Fundación de Historia Natural “Félix de Azara”, CEBBAD, Univ. Maimónides. Buenos Aires, Argentina.

XXIV Jornadas Argentinas de Paleontología de Vertebrados, San Rafael, Mendoza, Argentina. Mayo, 2009.