REASSESSMENT OF LAPLATASAURUS ARAUKANICUS (SAUROPODA: TITANOSAURIA), FROM THE LATE CRETACEOUS OF PATAGONIA, ARGENTINA

PABLO A. GALLINA; ALEJANDRO OTERO

Diamante

Jornada; 29 Jornadas Argentinas de Paleontología de Vertebrados; 2015

The original materials assigned to Laplatasaurus araukanicus Huene 1929 comes from five different localities from the Upper Cretaceous (Anacleto Formation) of northern Patagonia. The taxon validity and constituency is problematic. Only the lectotype material (one tibia and one fibula) is recognized as valid, but the remaining materials ever assigned to Laplatasaurus remained unresolved. Here, we review all the materials that have hitherto been assigned to this taxon, expand the diagnosis, and include it into an updated phylogenetic data matrix for the first time. Laplatasaurus araukanicus Huene 1929 is retained only for the lectotype material, as suggested by other authors, by the presence of a deep cnemial fossa, extending more than one third the length of the tibia and an extremely developed anterior fossa on the proximal end of the fibula, laterally delimited by a thick margin. The materials from Rancho de Ávila are referred to cf. Bonitasaura sp. by the absence of diagnostic characters of Laplatasaurus and by the presence of diagnostic features shared with Bonitasaura as well as the stratigraphic congruence of the occurrence (Bajo de la Carpa Formation). The other remains were referred as Lithostrotia indet. Although the support values of the in-group nodes are invariably low, the phylogenetic analysis recovered Laplatasaurus as the sister taxon of Uberabatitan riberoi in a clade supported by the presence of a longitudinal fossa on the posterior face of fibular midshaft. This clade is nested within Titanosauria in a clade formed by ((Laplatasaurus + Uberabatitan) + (Bonitasaura + (Futalognkosaurus + Mendozasaurus)).