NOVEL INSIGHT INTO THE ORIGIN OF THE GROWTH DYNAMICS OF SAUROPOD DINOSAURS

IGNACIO CERDA; ANUSUYA CHINSAMY; DIEGO POL; CECILIA APALDETTI; ALEJANDRO OTERO; JAIME POWELL; RICARDO MARTÍNEZ

Mar del Plata

Congreso; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2015

Sauropod dinosaurs are considered to have uninterrupted rapid rates of growth (inferred from the lacks of growth marks in their long bones during most of its ontogeny), which differs from their more basal relatives (non-sauropod sauropodomorphs or ?prosauropods?), which have a slower cyclical growth dynamics (evidenced by the cyclical deposition of growth marks during all the ontogeny). Nevertheless, this idea has been supported by histological examinations in a reduced number of basal sauropodomorph taxa. Here we examine the bone microstructure of several sauropodmorph dinosaurs, including ?prosauropods? (Riojasaurus incertus, Coloradisaurus brevis, Massospondylus carinatus, Leyesaurus marayensis, Leonerasaurus taquetrensis, Mussaurus patagonicus and Adeopapposaurus mognai), as well as sauropod taxa (Lessemsaurus sauropoides, Volkheimeria chubutensis and Patagosaurus fariasi). The examined histological sections where obtained from the mid-shaft of thirteen femora. With the exception of Mussaurus, growth marks in the whole cortex were observed in all ?prosauropods? and also in Lessemsaurus. Whereas in Volkeimeria only a single growth marks was recorded, several poorly defined annuli where observed in the outer cortex of Patagosaurus. Our results agree with the current consensus that the plesiomorphic condition for the sauropodomorpha is cyclical growth dynamics. However, we show here that uninterrupted and sustained rapid growth (the so called ?sauropod pattern?) also occurred in at least some prosauropods (e.g. Mussaurus) and the cyclical growth strategy was also present in the basal sauropods as Lessemsaurus. Our study reveals that the ?typical? sauropod growth pattern arose more than one time during the evolution of Sauropodomopha and such pattern was not exclusive of Sauropoda.