Validation of a new morphological diagnostic criterion in Mauritian giant tortoises of the genus Cylindraspis ( Cryptodira, Testudinidae ) thanks to paleoproteomics

A collection of Cylindraspis Fitzinger, 1835, subfossils from Mare aux Songes (Mauritius, 4,200 years BP) has recently been described. At the end of this preliminary description, only some of the 216 tortoise bones could be identified using anatomical criteria and the question of a potential new diagnostic criterion for identifying the two different Mauritian species, Cylindraspis inepta (Günther, 1873) and Cylindraspis triserrata (Günther, 1873), raised from the observations of certain skulls. In the present study, all specimens were analysed using paleoproteomics (MALDI-FTICR and LC-MS/MS), with the objectives of identifying the subfossils remaining unidentified and also ruling on the viability of the potential new diagnostic criterion, the baso-caudal face morphology of the supraoccipital crest. In addition to the species identification in 214 cases, the results of the paleoproteomic analyses led to the revision of the reference peptide profiles for the two Mauritian Cylindraspis species through the discovery of four new marker peptides and the reassignment of the diagnostic masses for the three marker peptides already known. Finally, being consistent with all the anatomical pre-identifications made on the basis of the baso-caudal face morphology of the supraoccipital crest, the paleoproteomic results validate this cranial region as a new morphological diagnostic criterion for identifying the two Mauritian Cylindraspis species.