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

IGNACIO A. CERDA; ANUSUYA CHINSSAMY; DIEGO POL; CECILIA APALDETTI; ALEJANDRO OTERO; JAIME POWELL; RICARDO MARTÍNEZ

Mar del Plata

Jornada; Reunion 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), which have a slower cyclical growth dynamics (evidencedby the cyclical deposition of growth marks during all the ontogeny). This idea has been supported by histological examinations in a rather limited number of basal sauropodomorphs. Here, we examine the bone microstructure of several basal non-sauropod sauropodomorphs (i.e., 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 were obtained from the mid-shaft of thirteen femora. Except for Mussaurus, growth marks in the whole cortex were observed in all basal sauropodomorphs and also in Lessemsaurus, whereas in Volkheimeria only a single growth mark was recorded and several poorly defined annuli were observed in the outer cortex of Patagosaurus. Our results agree with the currentconsensus that the plesiomorphic condition for the sauropodomorpha is cyclical growth dynamics. However, our findings show that uninterrupted and sustained rapid growth (the so called ?sauropod pattern?) also occurred in at least some basal forms (e.g., Mussaurus) and the cyclical growth strategy was also present in basal sauropods as Lessemsaurus. Our study reveals that the ?typical? sauropod growth pattern arose more than once during the evolution of Sauropodomorpha and such a growth pattern was not exclusive to the Sauropoda.