Neuroanatomy of Secernosaurus koerneri (?Kritosaurus australis?): first endocranial description for a saurolophine hadrosaurid in South America, a descriptive and comparative approach

CRUZADO-CABALLERO, PENELOPE; BECERRA, MARCOS G.; TABORDA, JEREMÍAS R A; PAULINA CARABAJAL, ARIANA

San Luis

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

Universidad Nacional de San Luis

The endocranial morphology of Secernosaurus koerneri (Brett-Surman, 1979; = Kritosaurus australis, Bonaparte, Franchi, Powell and Sepulveda, 1984) from Los Alamitos Formation (Late Campanian - early Maastrichtian), was studied using CT-scans of three fragmentary braincases (MACN-RN 02, 142 and 144). With this information we obtained a hypothetical brain model for this species, which is described here by first time. As in other hadrosaurids, the cranial endocast shows, in dorsal view, laterally expanded rounded cerebral hemispheres and a narrow hindbrain that bears a conspicuous dural peak. The olfactory tracts are short and robust, separated from the cerebral hemispheres by a marked constriction. The olfactory bulbs are small, oval and slightly divergent. The passage for the optic nerve (CN II) is large, circular, and separated from its counterpart. The oculomotor (CN III), trochlear (CN IV) and facial (CN VII) nerves are only partially represented. The infundibulum is circular and its posterior margins indicate a shallow dorsum sellae. The exit for the trigeminal nerve (CN V) is the largest. The foramina for the glossopharingeal and vagoaccessory nerves can be only externally delimited, converging with the anterior rami of the hypoglossal nerve (CN XII1), which is also divided into two rami. The caudal middle cerebral vein, and probably the orbitocerebral vein can be recognizable, as features of the inner ear. The comparative neuroanatomy of Secernosaurus koerneri within a phylogenetic framework with hadrosaurid species from northern landmasses (e.g., Kritosaurus Brown, 1910; Edmontosaurus Lambe, 1917; and others) indicates a rather conservative brain morphology for Cretaceous hadrosaurids.