Not just a pretty face: Anatomical peculiarities in the postcranium of rebbachisaurids (Sauropoda: Diplodocoidea) based on South American forms.

APESTEGUÍA, S., GALLINA, P. A. & HALUZA, A.

Marrakech, Marruecos

Congreso; 1er Congrès International sur la Paléontologie des Vertébrés du Nord de l’Afrique; 2009

Université Cadi Ayyad UCAM - Marrakech - Societé Marrocaine d'Herpetologie

Rebbachisauridae are poorly known “bizarre” sauropods with only two nearly complete skeletons collected: Limaysaurus tessonei from Patagonia and Nigersaurus taqueti from Niger. Whereas the later taxon allowed the understanding of their cranial novelties, South American species show some peculiarities in the postcranium. Lymaysaurus tessonei, Cathartesaura anaerobica and a new form (MMCH-Pv-49) from Villa El Chocón, exhibit peculiar pectoral girdles and the loss of the hyposphene- hypantrum accessory articulations in their amphyplathian dorsal vertebrae. Actually, the postzygapophyses are not only devoid of hyposphenal locks but additionally show a curved postzygapophyseal eave that allows a slicing over the corresponding structure in the prezygapophysis, a curved concave and elongated platform continuous along both prezygapophyses: the prezygapophyseal shelf. In the same way that the acquiring of “ball and socket” opisthocoelous centra in macronarians optimized the mobility (controlled by bifid hyposphenes in basal forms), the “U-eave and shelf complex” of rebbachisaurids permitted an increased flexibility between successive vertebrae along the axial skeleton. Upper Cretaceous sauropods acquired more flexible vertebral columns along different paths. However, while in titanosaurs the increased mobility occurred related to the centrum shape, in rebbachisaurids responded as a complex system in the neural arch. Furthermore, whereas macronarians show large centra, rebbachisaurids underwent a minimization of the centrum changing the larger articular structure between vertebrae from ventral to dorsal respect to the neural canal. These changes in both sauropod lineages probably had an outstanding relevance in the diversity and ecological roles that sauropods underwent in Cretaceous terrestrial ecosystems.