Postcranial anatomy of Bonitasaura salgadoi (Sauropoda, Titanosauria) from the Late Cretaceous of Patagonia

ABSTRACT

Bonitasaura salgadoi, from the Bajo de la Carpa Formation (Santonian), Río Negro, Argentina, is a well-preserved titanosaur. Previously described cranial material of Bonitasaura demonstrated the presence of square jaws in titanosaurs, but the nearly complete postcranium of the holotype specimen remains mostly undescribed. We present an osteological description of this material, which includes cervical, dorsal, and caudal vertebrae, elements of the pectoral and pelvic girdles, as well as forelimbs and hind limbs. Characteristics of the axial skeleton suggest that the holotype represents an immature individual. The base of the neck was likely robust, based on the broad, rhomboidal neural spines in the vertebrae across the cervicodorsal transition. Bonitasaura is assigned to Titanosauria based on lateral constriction of the neural canal in the anterior cervical vertebrae, presence of anterior and posterior spinodiapophyseal laminae in the middle to posterior dorsal vertebrae, distolateral expansions of the middle dorsal vertebral neural spines, absence of hyposphene-hypantrum articulations in posterior dorsal vertebrae, anterior and middle caudal vertebrae with strongly procoelous centra, anterior caudal vertebrae with transverse processes extending beyond the posterior margin of the centrum, and other axial features. The appendicular anatomy of Bonitasaura also supports referral to Titanosauria based on characters such as the semilunar sternal plates, flat and rugose distal surfaces of the metacarpals, medial curvature of the proximal femur, posterior shallow fossa of the astagalus undivided, and mediolaterally expanded distal tibia. The gracile long bones further support placement within non-saltasaurine titanosaurs. Bonitasaura provides additional osteological data that will contribute to a better resolution of titanosaur phylogeny.

ACKNOWLEDGMENTS

The authors are deeply grateful to the Pincheira and Zuñiga families for their hospitality and kindness at ‘El Manzano,' Cerro Policía, in every field season (2003, 2004, 2008, and 2012). We especially note the help of F. Ávila, the paleontological guide of the 1922 Schiller and Roth expedition, who guided us to the fossiliferous area and passed away last year at 103 years of age, and E. Parodi, who showed us the exact location of the bones. We also thank all those who helped excavate the fossils across field seasons, specifically A. Carignano, J. González, F. Agnolín, L. Gaetano, L. Balarino, M. Cárdenas, G. Lío, M. de la Fuente, M. Pérez, A. Otero, L. Cruz, A. Haluza, F. Brissón Egli, L. Makádi, A. Ősi, J. Pazo, A. Navarro Falcón, M. Krause, F. Blanco Villalba, C. Papolio, M. Salinas (and his family), R. Juárez Valieri, F. Endres, E. Gómez, and Carlos Muñoz from the Museo de Cipolletti. Fossil preparation was carried out by J. González, M. Isasi, F. Gianechini, M. Mora Solé, and J. Pazo. The skeletal reconstruction of Bonitasaura was provided by J. González. N. Smith and J. Mitchell generously revised the English style of the manuscript. This contribution was greatly improved by detailed reviews from P. Mannion and J. Wilson and editor R. Butler. We thank the Jurassic Foundation and Fundación Félix de Azara for providing financial support for field work and laboratory work to P.A.G. and S.A., and the Secretaría de Cultura de Río Negro for excavation permits.