Osteology of Rebbachisaurus garasbae Lavocat, 1954, a diplodocoid (Dinosauria, Sauropoda) from the early Late Cretaceous–aged Kem Kem beds of southeastern Morocco

ABSTRACT

The holotype of the sauropod dinosaur Rebbachisaurus garasbae was discovered in infra-upper Cenomanian horizons of the Kem Kem region of southeastern Morocco in the 1940s and 1950s. The original materials included part of a vertebral column, some of which was found in articulation, and a scapula, a humerus, and an ischium. Of these remains, only the scapula and one of the dorsal vertebrae have been described, but in abbreviated form. Following complete preparation of the partial skeleton, careful examination and fitting of scores of fragments collected with these materials, and computed tomography imaging of the most complete vertebra, we present a complete description of the holotype of Rebbachisaurus garasbae. Our description identifies several autapomorphies of the dorsal and caudal vertebrae, both relating to the shape of the vertebrae and the architecture of their laminae. Based on our reassessment of its anatomy, Rebbachisaurus is recovered as a member of an Afro-European clade that includes Nigersaurus and Demandasaurus. Due to the large size of one of its dorsal vertebrae (ca. 1.45 m tall), Rebbachisaurus has been considered to be a large sauropod. The size of the vertebral centra and the length and cross-sectional area of the humerus of Rebbachisaurus, however, indicate this individual weighed 7915–12,015 kg, which is slightly larger than Amargasaurus but comparable in size to some individuals of Dicraeosaurus. The dorsal vertebrae of Rebbachisaurus and other rebbachisaurids have been suggested to be highly mobile, but results suggest that anatomical features of the vertebrae actually limited rotation and increased resistance to dorsoventrally directed forces applied to the transverse processes.

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ACKNOWLEDGMENTS

We thank B. Ledimet, J. Richir, P. Richir, R. Vacant, and F. D. Aisance for preparation of the specimens. J. Le Loeuff and P. Taquet kindly provided the field photographs used in Figure 2. Specimen photographs were taken by C. Lemzaouda of the MNHN with collaboration of the authors. Color scheme in Figure 16 was developed using ColorBrewer (v2.0). CT scans, processing, and 3D reconstructions were performed at the AST-RX (Accès Scientifique à la Tomographie à Rayons X) of the MNHN by F. Goussard. Thanks to K. Hoffman (Northwestern University), M. Lafkioui (Universiteit Gent), and J. Heath (University of Michigan) for sharing their knowledge of the culture and language of the Berber peoples of Morocco. We thank J. Whitlock for providing measurements of the Limaysaurus humerus, F. Dalla Vecchia for information about Histriasaurus, M. D'Emic for access to unpublished body size data and regressions, F. Fanti for unpublished photographs of Tataouinea, N. Ibrahim for sharing photographs of referred Rebbachisaurus specimen NMC 50844, and J. Carballido for discussion. We thank D. Pol and H. Zaher for providing advice about TNT and sharing an unpublished user guide. We thank J. Carballido, J. Fronimos, P. Mannion, and J. Whitlock for useful and detailed reviews of this paper. We are especially grateful to P. Sereno and B. Masek for providing access to specimens of Nigersaurus at the University of Chicago.