The appendicular skeleton of the titanosaur Bonatitan reigi Martinelli y Forasiepi: neither saltasaurinae affinities nor reduced forelimbs

GALLINA, P.; SALGADO, L.

La Rioja

Jornada; XXVII JAPV; 2013

Comisión Organizadora

In the context of a full revision of the titanosaur Bonatitan reigi Martinelli and Forasiepi, from Allen Formation (Campanian-Maastrichtian), Rio Negro province, the study of the appendicular anatomy has shed light both in osteology and systematics. Although not supported by a cladistic analysis, the original assignation to Saltasaurinae was based in three features; two axial and one appendicular. The appendicular character, considered by Martinelli and Forasiepi as diagnostic for the subfamily, is: “distal femoral condyles anteriorly exposed”. However, this condition has a wider distribution within Titanosauria, being present in several non-saltasaurinae titanosaurs, such as Lirainosaurus Sanz et al., Magyarosaurus Huene, Phuwiangosaurus Martin et al., and Rapetosaurus Curry Rogers and Forster. Besides, all comparisons between the appendicular bones of Bonatitan and saltasaurine evidence remarkably gracile proportions in the former (e.g., Robustness Indexes: Humerus, 0.27; Femur, 0.23; Tibia, 0.25). In the original description two specimens are recognized within the recorded material (the holotype and one referred specimen). Nonetheless, the revision shows at least the presence of five specimens based in relative size and individual bone proportions, as well as the recognition that the ulna referred to the smallest specimen is actually a metacarpal IV of a larger specimen. This reassignment, among other aspects, modifies the overall conception of a reduced forelimb, as can be seen in the mounted specimen from the Museo Argentino de Ciencias Naturales. The review of this species will improve our understanding of the sauropod faunal components of the uppermost Cretaceous of Argentina.