A new species of marine ophidiomorph lizard, Adriosaurus skrbinensis, from the Upper Cretaceous of Slovenia

A new species of the genus Adriosaurus Seeley, 1881, Adriosaurus skrbinensis, is described and diagnosed by the following unique features: presence of 30 dorsal vertebrae; much larger body size than that of A. suessi and A. microbrachis (about 60% larger); forelimbs much more reduced than the hind limbs, i.e., with a humerus/femur ratio of only 0.40; parietal foramen lying on the suture line between frontal and parietal; and anterior margin of the parietal convex anteriorly. Further features observed in A. skrbinensis, but obscured or poorly preserved in other adriosaurs, include intercentra articulating with (not fused or sutured to) cervical vertebrae; presence of high, rectangular neural spines on caudal vertebrae; very long chevron bones articulated to posterior ventral margin of caudal vertebrae; pubic bone with well-developed square anterior process and distinct pubic foramen. This new fossil suggests variability in the dorsal vertebrae count of Adriosaurus, ranging between 28 and 30. Similar to what has been observed in living scincids and anguids, there seems to be a direct relationship between axial elongation and shortening of the humerus in Adriosaurus. Cladistic analysis resulted in one shortest cladogram that places A. skrbinensis as the sister taxon to A. suessi.