REAPPRAISAL OF THE MORPHOLOGY AND PHYLOGENETIC RELATIONSHIPS OF THE ALLIGATOROID CROCODILIAN DIPLOCYNODON HANTONIENSIS (OWEN, 1846) FROM THE EOCENE OF HORDWELL, UNITED KINGDOM (original) (raw)

The alligatoroid Diplocynodon is by far the most common European eusuchian, being described or mentioned from more than 200 localities and including several species, nine of which are considered valid and their phylogenetic relationships analyzed. Despite being among the first Diplocynodon species to be named, Diplocynodon hantoniensis from the Late Eocene of England was never described and figured with a modern approach. Most of the updated information on the morphology of D. hantoniensis derives indirectly from the character codings used for the cladistic analyses, which are available in the literature since the early 1990s. Subsequent studies were largely relying on a single data matrix produced more than a decade ago providing different topologies according to the number of taxa included in the analysis and their degree of completeness. Here we present the result of the revision of the whole Hordwell Cliff collection hosted at the Natural History Museum in London. The study of several nearly complete, well-preserved skulls and lower jaws, as well as dozens of other cranial and postcranial remains, allowed us to re-evaluate the codings of a few characters: in D. hantoniensis, the dentary symphysis extends from the posterior half of the fourth alveolus (BMNH 30397) to the center of the fifth alveolus (BMNH 30396, R1043); the surangular-articular suture is strongly bowed laterally within the glenoid fossa; the lateral edges of the palatines are parallel posteriorly; the ectopterygoid-pterygoid flexure does not disappear during ontogeny; and the quadratojugal-jugal suture lies at the posterior angle of the infratemporal fenestra. The result of these changes produced, however, a general polytomy of all the Diplocynodon species included in the analysis, indicating that further morphological data is needed to resolve the phylogenetic relationships of the species of this clade. MD supported by Synthesys (FR-TAF 967, BE-TAF 4907, GB-3097) and by the Spanish Ministerio de Economia y Competitividad (CGL2011-28681).