Osteologia descrittiva e affinità filogenetiche dello scinco apodo europeo Ophiomorus punctatissimus

The topic of the thesis is the study of the osteology of the limbless skink Ophiomorus punctatissimus, endemic of the Peloponnese. A description of the connected skeleton and of the single cranial and postcranial bones is provided, using a disarticulated skeletonized specimen and the CT-scans of 3 whole specimens as reference material. Moreover, a phylogenetic analysis was conducted in order to study the relationships between this skink and the other European skinks. The morphology of the pelvic girdle and the pectoral girdle was remarkable. The girdles are vestigial and don't retain any trace of associated limbs. The pectoral girdle of O. punctatissimus is relatively well-developed and, excluding the limbs, retains all the osseous elements typical of non-limbless skinks. The pelvic girdle is extremely regressed, both in the sacral vertebrae, whose transverse processes are widely separated at their distal ends, and in the pelvic bones, which comprise completely fused ilea, ischia and pubes, detached from the sacrum and with the pubes of the two pelvic elements not in medial connection with each other. Based on this data, and considering that in the most phylogenetically close congeneric species there is a similar tendency towards pelvic reduction, it is possible to hypothesize that the more marked reduction of the pelvic girdle compared to the pectoral girdle could be associated to an asynchronous loss of the limbs, starting with the posterior limbs and then involving the anterior limbs. The study of the connected skeletons using the CT-scans also highlighted some characteristics that correspond to a burrowing ecomorph. In particular, in addition to the loss of limbs, the small size of the skull compared to the rest of the body, the fact that the skull is very elongated and uniformed to a short neck, the high number of presacral vertebrae and the reduced body lumen, can all be associated with this ecomorph. Additionally, the relatively small size of the orbits and the small auricular apertures seem to corroborate this thesi, although the presence of autotomic vertebrae in the tail suggests a context in which predation is still an important factor. The matrix for the phylogenetic analysis, modified from that of Genlaw (2011), was created with Mesquite and analyzed with TNT. It includes 121 cranial and postcranial characters. It includes 14 taxa of which 7 Scincidae, representing the totality of the European genera and of the species except one species, 1 Afro-asiatic skink and 7 taxa of other lizards. All the specimens for each taxon were inserted in the matrix as separate OTUs (Operational Taxonomic Unit), for a total of 18 OTUs, 4 of whom were OTUs of O. punctatissimus. The results indicate that the OTUs of O. punctatissimus are always grouped into a single clade, and that among the European skinks the genus Chalcides is the most phylogenetically close to Ophiomorus. Thanks to this analysis, a diagnostic combination of characters for O. punctatissimus was identified. It is hence demonstrated that the skeleton of this species, and those of European skinks in general, bears a phylogenetic signal useful to explore the relationships among the studied groups of squamates, although the obtained topologies partially differ from the results of the most recent molecular analyses.