Not just a pretty face: anatomical peculiarities in the postcranium of Rebbachisaurids (Sauropoda: Diplodocoidea)

Abstract

Rebbachisauridae are poorly known ‘bizarre’ sauropods with two nearly complete skeletons collected: Limaysaurus tessonei and Nigersaurus taqueti. Whereas the latter taxon allowed the understanding of their cranial novelties, other species show some peculiarities in the postcranium. L. tessonei, Rebbachisaurus garasbae and a new form (MMCH-Pv-49) from Villa El Chocón, Patagonia, exhibit peculiar pectoral girdles and the loss of the hyposphene–hypantrum accessory articulations in their amphiplathyan dorsal vertebrae. Actually, the postzygapophyses are not only devoid of hyposphenal locks but also additionally show a curved postzygapophyseal eave that allows a sliding over the corresponding structure of the anterior side of the neural arch, a curved concave and elongated platform continuous along both prezygapophyses: the prezygapophyseal shelf. As the ‘ball and socket’ opisthocoelous centra in macronarians optimised mobility, the ‘U-eaves and shelf complex’ of rebbachisaurids permitted wider movements between successive vertebrae. While in titanosaurs the increased mobility occurred related to the centrum shape, in rebbachisaurids it is related to a complex system in the neural arch. Furthermore, whereas macronarians show large centra, rebbachisaurids underwent a minimisation of the centrum. These changes in both sauropod lineages probably had an outstanding relevance in the diversity and ecological roles that sauropods experienced in Cretaceous terrestrial ecosystems.

Keywords:

• Rebbachisauridae
• vertebral articulation
• torsion movements

Acknowledgements

We thank Dr Jorge Calvo (CEPALB, Argentina) for allowing PAG to see L. tessonei, Dr Ronan Allain for permitting SA to see the holotype of R. garasbae that is under re-preparation, and for great improvement in this manuscript, Nour Eddine Jalil and the organisation committee of the NAVEP1 for the opportunity to present our results here, although they are mostly based on South American taxa, El Chocón crew who collected the specimens, Sebastián Vaccaro for technical assistance and Javier Ochoa who made the detailed drawings in Figure 2. We also thank Leonardo Salgado, Jeffrey Wilson and Heinrich Mallison for sharing their opinions on the subject.