Reinterpretation of the dorsal vertebrae of Argentinosaurus huinculensis (Sauropoda, Titanosauridae)

NOVAS, F. E.; EZCURRA, M. D.

Jornada; XXII JORNADAS ARGENTINAS DE PALEONTOLOGÍA DE VERTEBRADOS; 2006

Argentinosaurus huinculensis Bonaparte and Coria Río Limay Formation, Cenomanian, Neuquén Province, NW Patagonia), is one of the largest known dinosaurs. This titanosaurian, described by Bonaparte and Coria in 1993 (BC93),is represented by several postcranial bones, including 6 dorsal vertebrae. Comparisons with the almost complete dorsalseries of the Peiropolis titanosaurid from Brazil and Opistocoelicaudia skarzinskii Borsuk-Bialynicka rom Mongolia, allowa reinterpretion of the sequence of dorsal vertebrae of Argentinosaurus. We agree with BC93 in considering an almost completevertebra as D3. However, the remaining dorsals of Argentinosaurus require review. The isolated ?posterior dorsal?of BC93 constitutes a D4 because this vertebra closely matches the morphology of D3 mentioned above. ?D1? of BC93 resemblesD5 of the Peiropolis titanosaurid in the presence of a caudodorsally projected neural spine, prezygapophyseallamina well-developed and laterally excavated at its base, and prezygapophyses close to each other. Two ?united posteriordorsals? thus described by BC93 match the morphology of D6 and 7 of the Peirópolis titanosaurid, especially in thedorsolateral orientation and complex ventral morphology of transverse processes. ?D2? of BC93 seems to constitute D10or 11 based on the presence of a large, short and transversely wide centrum (constituting the largest centrum of the preservedvertebral sequence), subvertical neural spine, and postzygapophyses placed well below the level of the transverseprocesses. The following conclusions are reached: 1) cranial dorsals of Argentinosaurus are morphologically intermidiatebetween basal camarasauromorphs (with vertical neural spines) and advanced titanosaurids (with neural spinesstrongly inclined backwards); 2) in derived titanosaurids the transverse processes of cranial dorsals are laterodorsallyoriented, whereas in Argentinosaurus are horizontally projected, thus retaining a primitive condition. In sum, dorsalmorphology supports the hypothesis that Argentinosaurus constitutes a basal member of the Titanosauria.