New rebbachisaurid (Sauropoda, Diplodocoidea) skull remains from Candeleros Formation (Cenomanian), Neuquen Province, Argentina

PAULINA CARABAJAL, ARIANA; HALUZA, ALEJANDRO; CANALE, JUAN IGNACIO

La Rioja

Jornada; XXVII Jornadas Argentinas de Paleontología de Vertebrados; 2013

CRILAR

Rebbachisaurid remains are frequently recorded in the basalmost units of Neuquen Group. However, skull remains are scarce and particularly the braincase anatomy of the Argentinean taxa is poorly known. Here we report a new rebbachisaurid partial braincase and a right quadrate (MMCH-PV 63) recovered from Candeleros Formation. The braincase is fractured sagitally allowing the observation of the endocranial cavity. Latex endocasts were made of brain and inner ear. The braincase exhibits some traits similar to Nigersaurus and Limaysaurus, such as the orbitary vault of frontal strongly convex, crista antotica low and laterally compressed, and size and distribution of the cranial foramina. The large orbitocerebral foramen observed in Nigersaurus is absent in Limaysaurus and the new specimen. As in other sauropods the brain is anteroposteriorly short and laterally expanded. The olfactory tract is short and wide, and anteriorly projected as in Nigersaurus, rather than anterodorsally as in Diplodocus and Camarasaurus. The cerebral hemispheres are rounded and laterally expanded, visible in dorsal view as in Nigersaurus. In other diplodocoids (i.e., Diplodocus, Amargasaurus) the dorsal expansion is large, obscuring the dorsal morphology of the brain. In the new specimen is noteworthy the presence of a small floccular process, only known in Nigersaurus and the basal titanosauriform Giraffatitan whitin sauropods. The pituitary body is strongly projected posteroventrally as in Nigersaurus. Cranial nerve VI penetrates the pituitary fossa, as in other diplodocoids. The morphology of the inner ear strongly resembles that of Nigersaurus, like the dorsal orientation of the lateral semicircular canal. Comparisons with the braincase of Limaysaurus will improve our knowledge on the paleoneurology of Limaysaurinae. Furthermore, the identification of characteristic braincase traits of the clad has potential use on phylogeny.