Aigialosauridae

Aigialosauridae (from Greek, aigialos, meaning "seashore", and sauros, "lizard") is a family of Late Cretaceous semiaquatic pythonomorph lizards closely related to the mosasaurs. Regarded by some paleontologists as a distinct monophyletic group and by others as an adaptive grade within the basal mosasauroids, recent molecular and morphological data suggests that they are the oldest known members of the lineage leading to the mosasaurs.

Aigialosaurus is an extinct genus of Late Cretaceous marine or semiaquatic lizard classified as part of the family Aigialosauridae within the Mosasauroidea. Exclusively found in deposits of Cenomanian age near Hvar, Croatia, the genus contains one valid species, A. dalmaticus. According to recent molecular and morphological data, Aigialosaurus is the oldest known member of the lineage leading to large Cretaceous marine reptiles called mosasaurs, a group most closely related to snakes among living squamates. It was a relatively small reptile with a complete specimen measuring long.

Carsosaurus is a genus of extinct amphibious reptiles, in the mosasaur superfamily, containing only the species Carsosaurus marchesetti. It is known from a single individual from the Komen Limestone of Slovenia. The specimen is well-preserved, containing many different bones as well as some skin impressions and sternal cartilage. While more remains are needed to be certain, it is generally thought to belong to Aigialosauridae. In life, it was an amphibious creature that spent most of its time on land, although its later relatives were fully aquatic.

Opetiosaurus is an extinct genus of Late Cretaceous marine or semiaquatic lizard classified as part of the family Aigialosauridae within the Mosasauroidea. Exclusively found in deposits of Cenomanian age near Hvar, Croatia, the genus contain one valid species, O. bucchichi. It was a small reptile measuring long.