First comments on the Dicraeosaurid inner ear: the endocranial morphology of Amargasaurus cazaui studied using X-ray CT scans

PAULINA CARABAJAL, A.

Las Vegas

Conferencia; Society of Vertebrate Paleontology Annual Meeting; 2012

Society of Vertebrate Paleontology

The braincase of the sauropod dinosaur Amargasaurus cazaui from the Lower Cretaceous of Neuquén Province, Argentina represents the only dicraeosaurid neurocranial material known from South America (with the probable exception of a partially preserved natural endocast recently recovered from the Lower Cretaceous Mulichinco Formation, also in northern Patagonia). Furthermore, the morphology of the inner ear has not previously been described for any of the four known genera of this sauropod clade. The braincase of Amargasaurus has been CT scanned, allowing for a three-dimensional digital reconstruction of the endocranium (represented by the forebrain, midbrain, and hindbrain, plus the spaces related to the pineal and postparietal fenestrae) and inner ear. The labyrinth is dorsoventrally longer than the lagena, which is simple, conical, and relatively short compared to that of other sauropods. The anterior semicircular canal (ASC) is larger than the posterior semicircular canal (PSC), and the lateral semicircular canal (LSC) is markedly smaller than the PSC, similar to the morphology described for Diplodocus. In dorsal view, the angle formed by the ASC and PSC is approximately 90°. When the braincase is oriented with the LSC positioned in the horizontal plane, the occipital condyle is not as ventrally projected as had previously been stated, suggesting that the habitual posture of the head was similar to that reconstructed for Nigersaurus, with the muzzle pointing downward. However, further studies of the cranial anatomy, myology, and cervical vertebral morphology of Amargasaurus are needed before the range of head and neck movements in this taxon can be defined.