Aigialosauridae (from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

, ''aigialos'' = "seashore" and ''sauros''= lizard) is a family of

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger 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 ''creta'', ...

semiaquatic In biology, semiaquatic can refer to various types of animals that spend part of their time in water, or plants that naturally grow partially submerged in water. Examples are given below. Semiaquatic animals Semi aquatic animals include: * Ve ...

pythonomorph lizards closely related to the

mosasaur Mosasaurs (from Latin ''Mosa'' meaning the 'Meuse', and Greek ' meaning 'lizard') comprise a group of extinct, large marine reptiles from the Late Cretaceous. Their first fossil remains were discovered in a limestone quarry at Maastricht on ...

s. Regarded by some paleontologists as a distinct monophyletic group and by others as an adaptive grade within the basal

oids, recent molecular and morphological data suggests that they are the oldest known members of the lineage leading to the mosasaurs. The family is recognized as containing two species, normally classified into two genera; '' Aigialosaurus'' and '' Opetiosaurus''. When used as an adaptive grade rather than as an actual monophyletic group, many other basal mosasauroids of uncertain affinities are occasionally referred to as "aigialosaurs", such as the genera ''

Komensaurus ''Komensaurus'' is a genus of basal aigialosaurid mosasauroid from the Late Cretaceous period. It was found at Komen in Slovenia in limestone dating from the Cenomanian. It was earlier referred to as the "Trieste aigialosaur". In 2007, the typ ...

'', ''

Haasiasaurus ''Haasiasaurus'' is an extinct genus of early mosasaur, originally named "''Haasia''" by M. J. Polcyn ''et al.'', in honour of the palaeontologist Georg Haas (paleontologist), Georg Haas. (The original name was a junior homonym of ''Haasia'' Bol ...

'', ''

Carsosaurus ''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 that lived during the Upper Cretaceous in what is now Slovenia. ...

'' and ''

Dallasaurus ''Dallasaurus'' ("Dallas lizard") is a basal mosasauroid from the Upper Cretaceous of North America. Along with ''Russellosaurus'', ''Dallasaurus'' is one of the two oldest mosasauroid taxa currently known from North America. It is also the small ...

'' and even entire mosasaur clades, such as the

Tethysaurinae The Tethysaurinae are a subfamily of mosasaurs, a diverse group of Late Cretaceous marine squamates. Members of the subfamily are informally and collectively known as "tethysaurines" and have been recovered from North America and Africa. Only two ...

. The term "plesiopedal mosasaurs" or "mosasaurs with a plesiopedal limb condition" is a more formal way to refer to such primitive species firmly within the family Mosasauridae.

Description

Aigialosaurids were semi-aquatic lizards that inhabited shallow marine environments in the ancient

Tethys Ocean The Tethys Ocean ( el, Τηθύς ''Tēthús''), also called the Tethys Sea or the Neo-Tethys, was a prehistoric ocean that covered most of the Earth during much of the Mesozoic Era and early Cenozoic Era, located between the ancient continents ...

, the only known fossils having been recovered from

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. Their skulls are similar to the skulls of more derived mosasaurs, though the postcranial skeleton is far more similar to that of terrestrial lizards.

Classification

The systematics and taxonomy of the Aigialosauridae is controversial and has a problematic history. Despite thorough reviews of the relationships between early Mosasauroidea and redescriptions of the two normally recognized aigialosaurid genera, ''Aigialosaurus'' and ''Opetiosaurus'', the status of the family remains uncertain. Dutchak & Caldwell (2009) designated ''Opetiosaurus'' as a junior synonym of ''Aigialosaurus'' (as ''Aigialosaurus bucchichi''), which suggested a very close relationship between the two. Their own analysis does not strictly support such a conclusion, and neither do subsequent analyses. Indeed, analyses done by Madzia & Cau (2017) show that the two genera are not necessarily more closely related to each other than either is to more derived mosasauroids, suggesting not only that ''Opetiosaurus'' is a valid genus, but also calling the validity of the Aigialosauridae as a monophyletic group into question.

References

{{Taxonbar, from=Q404316 Cretaceous lizards Cenomanian first appearances Prehistoric reptile families Mosasaurs