Adriosaurus
Adriosaurus is an extinct genus of squamate which lived in what is now Slovenia and other parts of Europe during the Late Cretaceous. It was small, snake-like reptile, with type species measuring up to 30 cm (12 in) in length. This is the first fossil record of vestigial limbs in lizards.[3][4] It lost its manus and forearm completely in order to elongate its axial skeleton. These unique anatomical features led to discussions of the evolutionary patterns of limb reduction in Squamata.[5]
Adriosaurus includes three species: A. microbrachis (“micro”, meaning small, and “brachis”, meaning arm, referring to the vestigial forelimb composed of only the humerus),[5] A skrbinensis (named after the location where they found the fossil, Skrbina, northwest of Komen, Slovenia) and A. suessi. However, A. microbrachis lacks many crucial characters to be qualified for cladistic analysis, thus it's not included in the list of terminal taxa.[6]
Adriosaurus was first described by Seeley (1881) based on a single specimen from near Comen, Slovenia. This fossil consists of the posterior half of the vertebral column, the pelvis and hindlimbs. Later Nopcsa (1908, 1923) described a nearly complete skeleton from Hvar, Croatia. However, at that time, Nopsca's systematic conclusions were not accurate. Michael S. Y. Lee and Michael W. Caldwell redescribed Adriosaurus suessi specimen NHMR2867.[7]
In 2004, Michael S. Y. Lee and Michael W. Caldwell reevaluated Acteosaurus crassicostatus which was based on a small lizard fossil found in Comen, Slovenia. They classified this into A. suessi rather than a new species.[8][9]
In 2007, Michael W. Caldwell and Alessandro Palci described a new species from Adriosaurus. The only specimen they had for A. microbranchis (MCSNT 7792) was an articulated specimen missing the skull, and part of the cervical and caudal skeleton.[5]
In 2010, Michael W. Caldwell and Alessandro Palci described A. skrbinensis. This new species was about 60% larger than the other two known species within Adriosaurus. The specimen SMNH 2158 was found in a small village in Komen, Slovenia. It's a relatively well-preserved natural molds specimen with most of the skull, parts of the vertebrae, parts of limbs and pelvic girdle.[6]
