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An incomplete Upper Cretaceous titanosaur (Sauropoda) braincase: new insights on the dinosaurian inner ear and endocranium
An incomplete braincase from the Upper Cretaceous Portezuelo Formation of northwestern Patagonia (Neuquén Province, Argentina) is described. The specimen preserves the lateral walls formed by the laterosphenoid, probably part of the orbitosphenoid, prootic, the exoccipital-opisthotic complex and fragments of the frontal, parietal and basisphenoid. Both inner ears are preserved allowing the production of latex endocasts. The external and internal morphology of the laterosphenoid and the prootic, the absence of a floccular recess, and the morphology and position of the cranial nerves V-VII, the oval window and the metotic foramen indicate that the new braincase belongs to a sauropod dinosaur, probably a titanosaur. The morphology of the inner ear is also reminiscent of that of Sauropoda, which is characterized by the presence of a simple, short and conical lagena, a posterior semicircular canal that is larger than the lateral semicircular canal, an anterior semicircular canal that is larger than the other two, and an angle between the vertical semicircular canals (anterior and posterior) of approximately 90°.
Braincase MCF-PVPH-765 in A, left and B, right lateral views, with drawing counterparts A’ and B’: Bsph, basisphenoid; ca, crista antotica; Eo-Op, exoccipitalopisthotic complex; F, frontal; fo, fenestra ovalis; met, metotic fenestra; Lsph, laterosphenoid; Orb, orbitosphenoid; P, parietal; pop, paroccipital process; Pro, prootic; vasc?, probable vascular foramen; pv?, pituitary vein?; II, III, IV, V, VI, VII: cranial nerves.