The Appendicular Osteology of Patagotitan Mayorum (Dinosauria, Sauropoda)

ABSTRACT

Its huge size, excellent preservation, and completeness make Patagotitan mayorum a unique opportunity to explore the anatomy, paleobiological, and phylogenetic aspects linked to gigantism within Sauropoda. In this regard, we describe the appendicular skeleton of this titanosaurian species from the late Albian-aged Cerro Barcino Formation of Chubut Province, Argentina. The diagnosis of Patagotitan mayorum is revised, increasing the number of identified autapomorphies (i.e., lateral surface of the scapular blade with two divergent crests; anterior surface of proximal humerus with paired muscle scars; combined bulges on the deltopectoral area of the humerus; ischium with well-developed and sharp ridge projecting from the ischial tuberosity to the distal blade). Several diagnostic characters of this species correspond to osteological correlates associated to appendicular musculature (e.g., Mm. deltoideus scapularis, deltoideus clavicularis, and teres major; M. coracobrachialis; Mm. supracoracoideus/deltoideus clavicularis and latissimus dorsi; Mm. flexor tibialis 3 and adductor femoris 2), which we discuss in the context of sauropod evolution. In the light of a modification of the scaling equation previously proposed and adjusting the long bone circumference for the humeri of Patagotitan, a new body mass estimate of this species ranges between 42–71 tons, with a mean value of 57 tons. Although considerably less than the value obtained by the original linear equation, the corrected quadratic equation used here provides a mean body mass estimate that is more consistent with those derived from volumetric reconstructions of Patagotitan.

ACKNOWLEDGMENTS

We would like to thank all the people who participated in fieldwork during the excavation of Patagotitan at ‘La Flecha’ ranch, as well as the skillful preparation of the collected materials that technicians performed. We thank P. May and Research Casting International for assistance in laser-scanning 3D editing during this project, and D. Pol (Museo ‘Egidio Feruglio’) for his suggestions. Comments of Associate and Technical Editors as well as reviewers P. Mannion and E. Gorscak highly improved this contribution. This project was possible thanks to the following financial support by ANPCyT: PICT 2015-0504 (to A.O.), PICT 2014-0668 and PICT 2017-1925 (to J.L.C.).