''Aigialosaurus'' is an extinct genus of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

marine or semiaquatic lizard classified as part of the family

Aigialosauridae Aigialosauridae (from Ancient Greek, Greek, ''aigialos'', meaning "seashore", and ''sauros'', "lizard") is a family of Late Cretaceous semiaquatic Pythonomorpha, pythonomorph lizards closely related to the mosasaurs. Regarded by some paleontologi ...

within the

Mosasauroidea Mosasauroidea is a superfamily of extinct marine lizards that existed during the Late Cretaceous. Basal members of this group consist of small semiaquatic forms with terrestrial limbs ("plesiopedal"), while laters members include larger fully ...

. Exclusively found in deposits of

Cenomanian The Cenomanian is, in the International Commission on Stratigraphy's (ICS) geological timescale, the oldest or earliest age (geology), age of the Late Cretaceous epoch (geology), Epoch or the lowest stage (stratigraphy), stage of the Upper Cretace ...

age near

Hvar Hvar (; Chakavian: ''Hvor'' or ''For''; ; ; ) is a Croatian island in the Adriatic Sea, located off the Dalmatian coast, lying between the islands of Brač, Vis (island), Vis and Korčula. Approximately long, with a high east–west ridge of M ...

Croatia Croatia, officially the Republic of Croatia, is a country in Central Europe, Central and Southeast Europe, on the coast of the Adriatic Sea. It borders Slovenia to the northwest, Hungary to the northeast, Serbia to the east, Bosnia and Herze ...

, the genus contains one valid species, ''A. dalmaticus''.Madzia, D., Cau, A. (2017)
Inferring "weak spots" in phylogenetic trees: application to mosasauroid nomenclature
. PeerJ 5:e3782 According to recent molecular and morphological data, ''Aigialosaurus'' is the oldest known member of the lineage leading to large Cretaceous marine reptiles called

mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Ancient Greek, Greek ' meaning 'lizard') are an extinct group of large aquatic reptiles within the family Mosasauridae that lived during the Late Cretaceous. Their first fossil remains wer ...

s, a group most closely related to

snake Snakes are elongated limbless reptiles of the suborder Serpentes (). Cladistically squamates, snakes are ectothermic, amniote vertebrates covered in overlapping scales much like other members of the group. Many species of snakes have s ...

s among living

squamate Squamata (, Latin ''squamatus'', 'scaly, having scales') is the largest Order (biology), order of reptiles; most members of which are commonly known as Lizard, lizards, with the group also including Snake, snakes. With over 11,991 species, it i ...

s.Grigoriev, D. V. (2013). "Redescription of ''Prognathodon lutugini'' (Squamata, Mosasauridae)." ''Proceedings of the Zoological Institute RAS'', 317(3): 246-261. It was a relatively small reptile with a complete specimen measuring long. Another primitive mosasauroid, ''

Opetiosaurus ''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 ...

'', was suggested to represent a second species of ''Aigialosaurus'' in 2009, "''Aigialosaurus bucchichi''",Dutchak, Alex R.; and Caldwell, Michael W. (2009
"A redescription of ''Aigialosaurus'' (= ''Opetiosaurus'') ''bucchichi'' (Kornhuber, 1901) (Squamata: Aigialosauridae) with comments on mosasauroid systematics".
''Journal of Vertebrate Paleontology'' 29 (2): 437-452. though this conclusion has not been supported by recent analyses.

References

Aigialosauridae Fossil taxa described in 1892 Taxa named by Dragutin Gorjanović-Kramberger {{paleo-lizard-stub