Affiliation:
1. Mécanismes Adaptatifs et Évolution, UMR 7179, MNHN, CNRS Muséum national d'Histoire naturelle 55 rue Buffon, CP55 Paris 75005 France
2. Centre de Recherche en Paléontologie – Paris, UMR 7207, MNHN, SU, CNRS Muséum national d'Histoire naturelle 8 rue Buffon, CP38 Paris 75005 France
Abstract
AbstractVarious terrestrial tetrapods convergently evolved to gigantism (large body sizes and masses), the most extreme case being sauropod dinosaurs. Heavy weight‐bearing taxa often show external morphological features related to this condition, but also adequacy in their limb bone inner structure: a spongiosa filling the medullary area and a rather thick cortex varying greatly in thickness along the shaft. However, the microanatomical variation in such taxa remains poorly known, especially between different limb elements. We highlight for the first time the three‐dimensional microstructure of the six limb long bone types of a sauropod dinosaur, Nigersaurus taqueti. Sampling several specimens of different sizes, we explored within‐bone, between‐bones, and size‐related variations. If a spongiosa fills the medullary area of all bones, the cortex is rather thin and varies only slightly in thickness along the shaft. Zeugopod bones appear more compact than stylopod ones, whereas no particular differences between serially homologous bones are found. Nigersaurus' pattern appears much less extreme than that in heavy terrestrial taxa such as rhinoceroses, but is partly similar to observations in elephants and in two‐dimensional sauropod data. Thus, microanatomy may have not been the predominant feature for weight‐bearing in sauropods. External features, such as columnarity (shared with elephants) and postcranial pneumaticity, may have played a major role for this function, thus relaxing pressures on microanatomy. Also, sauropods may have been lighter than expected for a given size. Our study calls for further three‐dimensional investigations, eventually yielding a framework characterizing more precisely how sauropod gigantism may have been possible.
Funder
H2020 European Research Council
Subject
Paleontology,Ecology, Evolution, Behavior and Systematics