A possible dicraeosaurid (Sauropoda, Diplodocoidea) cranial endocast from the Early Cretaceous of Patagonia

PAULINA CARABAJAL, A.; CORIA, R. A.; CURRIE, P.J; KOPPELHUS, E.

Buenos Aires

Jornada; XXVI Jornadas Argentinas de Paleontología de Vertebrados; 2012

Universidad Maimónides

The dorsal part of a cranial endocast (MLL-003) was collected from terrestrial sandstones of the lower section of the Mulichinco Formation (Valanginian) that outcrops in central Neuquén Province. It consists of cemented sandstone that preserves the endocranial morphology in detail, but not the cranial nerves. Some structures -- such as the dural expansion, the dorsal portion of the medulla oblongata, the cerebrum and the optic lobes – are preserved. As in most sauropods, the floccular process is absent. The bones that enclosed the endocranial cavity are missing, except for small pieces of the frontal and the laterosphenoids. Posteriorly, these frontal fragments frame what seems to be the pineal foramen, which is also present in Amargasaurus Salgado and Bonaparte 1991, Camarasaurus Cope 1877, Dicraeosaurus Janensch 1914, and Diplodocus Marsh 1878. A possible cast of the postparietal foramen can be observed posterodorsally; this structure is also present in the previously mentioned dicraeosaurids and in Tornieria Sternfern 1911. The braincase (MACN-N-15) of the type of Amargasaurus cazaui (from the Barremian of Argentina) is complete and undistorted. The cranial endocast and inner ear of this taxon have been studied using CT scans, and represent the only available endocranial information for a South American dicraeosaurid. This makes specimen MLL-003 particularly relevant. The presence of a pineal foramen and a possible postparietal foramen suggests this specimen is more likely related to Amargasaurus and Dicraeosaurus than it is to Titanosauriformes.