Growth dynamics of sauropodomorph dinosaurs

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

Calgary

Congreso; 77° Annual Meeting of the Society of Vertebrate Paleontology; 2017

Society of Vertebrate Paleontology

The Sauropodomorpha comprise of the more basal members, the non-sauropodsauropodomorphs, and the more derived members of the clade, the sauropod dinosaursamong which are the largest terrestrial vertebrates that ever lived. The basalsauropodomorph dinosaurs are reported to have cyclical growth dynamics (evidenced by the cyclical deposition of growth marks during ontogeny), while the sauropods, are considered to have uninterrupted rapid rates of growth (inferred from the lacks of growth marks in their long bones during ontogeny). These deductions pertaining to the growth dynamics of the Sauropodomorpha have largely been derived from histological studies of only a few basal taxa, and several more derived sauropod taxa (Neosauropoda). Here we examine a comprehensive sample of the bone microstructure of thirteen femoraof sauropodomorph dinosaurs, which includes seven basal non-sauropodsauropodomorphs (i.e., Riojasaurus incertus, Coloradisaurus brevis, Massospondylus carinatus, Leyesaurus marayensis, Leonerasaurus taquetrensis, Mussaurus patagonicus and Adeopapposaurus mognai), and a few sauropods (Lessemsaurus sauropoides, Volkheimeria chubutensis and Patagosaurus fariasi).Although our results agree that the plesiomorphic condition for Sauropodomorpha is cyclical growth dynamics, we found that the hypothesized dichotomy between the growth patterns of basal and more derived sauropodomorphs is not supported. Our findings revealed that except for Mussaurus, growth marks occur throughout the cortex in all basal sauropodomorphs, but were also found to occur in the sauropod, Lessemsaurus. Additionally, a single growth mark was recorded in Volkheimeria, while several poorly defined annuli where observed in the outer cortex of Patagosaurus. Thus, our results agree with the current consensus that the plesiomorphic condition for the sauropodomorpha is cyclical growth dynamics. However, our findings show that the uninterrupted and sustained rapid growth (the so called ?sauropod pattern?) also occurred in the basal taxon, Mussaurus. We also found that the sauropod-like growth dynamics of uninterruptedand sustained rapid growth also occurred in some basal sauropodomorphs.Furthermore, we found that some basal sauropods retained the plesiomorphic cyclical growth patterns. Thus, our findings show that among the sauropodomorpha the basal taxa exploited different growth strategies, but the more derived Eusauropoda successfully utilize rapid, uninterrupted growth strategies.