endocranial morphology of Gavialis gangeticus using CT scans: brain, inner ear, and pneumaticity

BONA, P.; PAULINA CARABAJAL, A.

Barcelona

Congreso; 10 International Congress of Vertebrate Morphology; 2013

International Society of Vertebrate Morphology

The skull of an adult specimen of Gavialis gangeticus was CT scanned and 3D models of the brain, inner ear, and pneumatic cavities were made. The cranial endocast is sub-horizontal, with cephalic and pontine flexures poorly marked, and a midbrain relatively more elongated than in Caiman and Crocodylus. The cerebral hemispheres are laterally rounded and the dorsal surface shows small vascular impressions indicating the presence of thin dorsal venous sinuses. There are small orbitocerebral and dorsal head veins. Behind the dorsum sellae, a small passage for the basilar artery communicates with the posterior section of the pituitary fossa. Cranial Nerve (CN) XII has a single root on the endocast but two external openings lateral to the occipital condyle. Another two foramina lateral to the occipital condyle correspond to the metotic foramen and the internal carotid artery. A branch from the metotic passage, the two branches of CN VII and the CN V2 have connection with the middle ear cavity. In the inner ear the angle formed between the anterior and posterior semicircular canals is approximately 90° and the lagena is extremely short. The anterior semicircular canal is larger than the posterior, which is similar in size to the lateral canal. The paratympanic system has three interconnected regions: the dorsal intertympanic recess (affecting the supraoccipital and the parietal), the lateral cavum tympanicum proper (connected through the siphonium with the foramen aereum posteriorly) and the ventral pharyngotympanic system (median and lateral Eustachian tubes). Compared with Alligator, the intertympanic recess is larger and more anteriorly developed, the siphonium is straight and shorter and the pharyngotympanic system is posteroventrally projected.