Redescription of Neochelys franzeni (Schleich, 1993) from the middle Eocene, Messel Pit, of Germany, and a revision of morphological characters with importance for Pleurodira phylogeny

Background. Neochelys franzeni (Schelich, 1993) is the only pleurodire or side-necked turtle from the middle Eocene, Messel Pit (the first UNESCO, World Natural Heritage Site in Germany, since 1995). The original description of the species is based on two specimens SMF ME 1091 (Holotype) and 715 (Paratype) housed at the Senckenberg Museum Frankfurt. The excellent preservation of complete and articulated skeletons of this species makes it a key taxon for understanding the evolution and phylogeny of the European Neochelys genus and its relationships with South American and African-Madagascar podocnemidids. Methods. Seven specimens of Neochelys franzeni, including hatchlings, juveniles, and adults were studied, and the information obtained for this species was included in a new compiled character-taxon matrix of Pleurodira, built from previous studies and new observations. Phylogenetic analyses were run using Parsimony algorithm on PAUP version 4.0a136 obtaining strict consensus trees after 10000 random replicates, boostrap values and Decay indices were also calculated to support the topology of obtained clades. Results. A revised diagnosis for the species is defined here, indicating that Neochelys franzeni differs from other members of the genus by the presence of a basisphenoid with a very acute anterior tip; an interparietal scute with a heart-like shape with a deep concave anteromedial margin; and a ridge running along the neural series of the carapace. Discussion. The phylogenetical analysis indicates that Neochelys spp. group is better resolved as closer to Erymnochelys madagascariensis-Peltocephalus dumerilanus inside Podocnemididae.