New information of the endocranial morphology of proterochampsids (euriapsid: archosauriformes) using ct-scans: comparison with living crocodylia

CARBAJAL, P.A.; TROTTEYN, MARÍA JIMENA; DESOJO, J. B.; BONA, PAULA; TABORDA, JEREMIAS R.A.

Congreso; 10th International Congress of Vertebrate Morphology (ICVM-10); 2013

The braincase anatomy of aquatic proterochampsid, a group of archosauriforms from the Triassic northwestern Argentina, has been recently known described based on new detailed descripcions. Additionaly, new Ctscans realized on Proterochampsa barrionuevoi (PVSJ 77), Chanaresuchus ischigualastensis (PVSJ 567), and Tropidosuchus romeri (PVLXXXX) from the Triassic northwestern Argentina, shed some light on the poorly known paleoneurology of these taxa. In order to a better undestanding of the endocranial morphology of this group, we compare the cranial endocast and inner ear whith extant aquatic pseudosuchians, such as Gavialis, Caiman, from which we made complete artificial brain and inner ear endocasts; and Crocodylus based on published information. Although the digital recontructions of the fossil taxa are incomplete, the partial endocasts show a similar morphology, represented by subhorizontal brains (cephalic and pontine flexures not well marded), with poorly developed dorsal expansions and relatively small pituitary. The cerebral hemispheres seem to be slighly lateraly projected unlike the strongly projected in living crocodylian. Partial labyrhynth of inner ear were reconstructed for Chanaresuchus and Tropidosuchus, showing slender semicircular canals. In Chanaresuchus the an angle between the anterior and posterior semicircular canals is approximatly 90-100º. The Ctscans showed that the middle ear of proterochampsids is poorly pneumatized relative to the studied extant forms. In Chanaresuchus and Tropidosuchus is noteworthy the presence of a foramen on the occipital plate, dorsal to the paroccipital process, comunicatig anteriorly with the middle ear. We identify this small passage as correlated with the cranioquadrate passage present in Crocodylia. Further research is necessary to determinate reather or not if this structure is homologous to the cranioquadrate and its implications for the aquatic life-style.