What's inside a sauropod limb? First three‐dimensional investigation of the limb long bone microanatomy of a sauropod dinosaur, <i>Nigersaurus taqueti</i> (Neosauropoda, Rebbachisauridae), and implications for the weight‐bearing function

Various 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 this condition, but also adequacy in their limb bone inner structure: a spongiosa filling medullary area rather thick cortex varying greatly thickness along shaft. However, microanatomical variation such remains poorly known, especially between different elements. We highlight for first time three-dimensional microstructure of six long types dinosaur, Nigersaurus taqueti. Sampling several specimens sizes, we explored within-bone, between-bones, size-related variations. If fills all bones, is thin varies only slightly Zeugopod bones appear more compact than stylopod ones, whereas no particular differences serially homologous are found. Nigersaurus' pattern appears much less that heavy as rhinoceroses, partly similar observations elephants two-dimensional data. Thus, microanatomy may have not been predominant feature sauropods. External features, columnarity (shared with elephants) postcranial pneumaticity, played major role function, thus relaxing pressures on microanatomy. Also, sauropods lighter expected given size. Our study calls further investigations, eventually yielding framework characterizing precisely how possible.