CRANIAL ANATOMY AND PHYLOGENETIC PLACEMENT OF THE ENIGMATIC TURTLE COMPSEMYS VICTA LEIDY, 1856

The skull of the enigmatic turtle Compsemys victa Leidy, 1856 is described. A number of unique characteristics are apparent, including the extremely thick nature of all cranial bones, the presence of rod-like epipterygoids, placement of the foramen posterius canalis carotici interni halfway along the contact between the pterygoid and basisphenoid, lack of cheek emarginations, and the reduction of the size of the cavum tympani relative to the orbit. Two differing global turtle analyses and one paracryptodiran analysis were performed to determine the phylogenetic placement of C victa. Both global analyses converged by placing C victa within Paracryptodira, herein defined as the most inclusive clade that includes Pleurosternon bullockii and Baena arenosa, but no species of living turtle, whereas the paracryptodiran analysis places C. victa outside of Baenoidea, herein defined as the least inclusive clade that contains P. bullockii and B. arenosa. Although a number of similarities are apparent between C. victa and the uncommon, extant testudinoid Platysternon megacephalum, the available data indicate that these similarities are convergent, likely due to their carnivorous diet. Taphonomic evidence reveals that basal paracryptodires, including C victa, preferred slow moving or ponded water environments. The riverine habitat preference of baenodds must therefore be derived.