Endocranial reconstructions of extinct turtles using μ-CT scans: new insights into brain and inner ear anatomy

PAULINA CARABAJAL, A.; STERLI, J.; MULLER, J.; JOYCE, W.G; WERNEBURG

Barcelona

Congreso; 10 International Congress of Vertebrate Morphology; 2013

International Society of Vertebrate Morphology

To shed more light on the still poorly known paleoneurology of turtles, we compared the endocranium and inner ear of the marine turtle Plesiochelys etalloni from the Upper Jurassic of Europe and the terrestrial turtle Naomichelys speciosa from the Early Cretaceous of North America using μ-computed tomography. As in extant turtles, the endocasts indicate poorly marked cephalic and pontine flexures, a short olfactory tract and bulbs, and similar cranial nerve patterns. In extant turtles, the small olfactory bulbs generally do not leave impressions on the frontals and cannot be identified on the artificial endocasts. However, the olfactory bulbs are clearly differentiated in the endocast of P. etalloni, indicating larger bulbs than in any other described extinct or extant turtle, and suggesting a higher capacity of olfaction in this taxon. The inner ears of both species are robust, with low lateral semicircular canals, and a short and conical lagena similar to that described for extant turtles such as Chelydra serpentina and Chrysemys scripta. The main differences between the two extinct taxa are (1) the relative extension of the dorsal expansion of the endocast above the cerebellum, which is strongly prominent in N. speciosa but very low in P. etalloni; (2) the relative length of the passage for cranial nerve VI, which is shorter in N. speciosa; (3) the shape of the semicircular canals, which are more strongly angled in P. etalloni; and (4) thecarotid circulation pattern. In P. etalloni the carotid circulation pattern is similar to extant cryptodires, while in N. speciosa the palatine artery is not covered ventrally by bone and the foramen pro ramus nervi vidiani (n. VII) is seen in ventral view. Further comparisons with extant forms, will determine whether or not the brain anatomy and inner ear of extinct turtles are informative for lifestyle.