New materials of rebbachisaurid sauropods from Huincul Formation at Villa El Chocón, Neuquén: a contribution to the knowledge of the appendicular anatomy of the group

LERZO, LUCAS; GALLINA, PABLO ARIEL; CANALE, JUAN IGNACIO; APESTEGUÍA, SEBASTIÁN

San Luis

Jornada; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2017

The Rebbachisauridae constitutes a group of medium to large sauropods recorded from both Lower and Upper Cretaceous rocks (Barremian-Turonian). Whereas much of the knowledge on their cranial anatomy comes from the highly modified skull of Nigersaurus (Sereno et al., 1999), the axial skeleton, including light presacral vertebrae with extremely laminated neural arches and elongated, petal-shaped neural spines, is known from several taxa. Nevertheless, the knowledge on the appendicular skeleton is scarce. New materials (MMCh PV70), including a complete left tibia and an incomplete left fibula collected in the Huincul Formation nearby El Chocón (Neuquén), permit to observe some characters for the group. The tibia is massive with its proximal end anteroposteriorly expanded and the distal end lateromedially wide. The cnemial crest is widely rounded and proximodistally extended, reaching the midlength of the tibia, as in Zapalasaurus and Limaysaurus. The cnemial fossa is deep and as length as the cnemial crest, unlike the shorter one present in Flagellicaudata. In lateral view, a slightly posterior bulge is present on the distal third, as observed in Limaysaurus and Zapalasaurus. The distal end is ovoidal and bears a narrow and deep lateral groove, differing from the variable condition present in Flagellicaudata. The distal fibula preserves a lateromedially expanded end with a marked astragalar process, unlike the less developed processes in Flagellicaudata. The distribution of these features within Diplodocoidea may represent synapomorphies for Rebbachisauridae. The inclusion of these appendicular characters in future cladistic analysis may contribute to achieve a better resolution of the in-group relationship.