Asprosaurus

''Asprosaurus'' () is an extinct genus of anguimorph lizard from the Late Cretaceous (Campanian) of South Korea. The genus contains a single species, ''A. bibongriensis'', which is the first Mesozoic lizard to have been discovered on the Korean peninsula. Initially classified as a possible monstersaurian, ''Asprosaurus'' has been subsequently suggested to be a probable mosasauroid, an extinct group of marine lizards during the Late Cretaceous.

Discovery and naming

The holotype of ''Asprosaurus'' (KDRC-BB4) is an associated specimen consisting of partial cranial and postcranial material. Initially interpreted as a turtle fossil, it was discovered in 2000 from the Seonso Conglomerate, one of the rock units that form the Boseong Bibong-ri Dinosaur Egg Site which also yielded the fossils of an ornithischian dinosaur ''Koreanosaurus'' and over 200 dinosaur eggs.

The generic name means "white lizard", named so because the fossil bones of the holotype were light in color, while Mesozoic fossil bones of the Korean peninsula are usually dark. The specific name is in reference to "bibongri", the type locality where the holotype was found. Because ''Asprosaurus'' is known only from fragmentary material, its relationships with other lizards are uncertain. However, features of the lower jaw suggest that it is an anguimorph, so the authors tentatively classified it as cf. Monstersauria, a clade which includes the living Gila monster.

In 2016, a potential second specimen (KDRC-BB5) was identified as ''Asprosaurus'' sp. This specimen is a partial skull donated in 2008 from an uncertain stratigraphic level within the same locality where the holotype of ''Asprosaurus'' was discovered. The specimen exhibits synapomorphies of Varanoidea and Monstersauria, and is the only known lizard skull fossil with preserved teeth in South Korea.

Description

''Asprosaurus'' has an estimated skull length of . It is probably larger than '' Chianghsia'', whose skull length is estimated up to in total and the snout-vent length around . The jugal of ''Asprosaurus'' preserves an angulated orbital margin, but lacks osteoderms and differs in shape from that of the Chinese monstersaurian ''Zhongyuanxi''.

Paleobiology

Various genera of large anguimorph lizards from the Late Cretaceous including ''Asprosaurus'' have been found in close proximity to the dinosaur eggs, so it is possible that these lizards are nest raiders. ''Asprosaurus'' might have been able to dig into nests using powerful forelimb muscles, which is inferred based on the morphology of the scapulocoracoid and humerus. If ''Asprosaurus'' instead represents a mosasauroid, it would have been either a fully aquatic or a semiaquatic marine lizard.

Classification

In 2015, the describers of ''Asprosaurus'' initially classified this taxon within Monstersauria. In their 2025 description of the new Late Cretaceous monstersaurian ''Bolg amondol'', Woolley and colleagues included ''Asprosaurus'' in a strictly morphology-based phylogenetic analysis, which recovered ''Asprosaurus'' within Mosasauroidea, forming a clade with ''Aigialosaurus'' and ''Eonatator''. The authors suggested that this result is unsurprising, as ''Asprosaurus'' lacks complete, diagnostic characters of monstersaurians, though they noted the uncertainty of its taxonomic affinities within Anguimorpha. The results of the morphology-based phylogenetic analysis are displayed in the cladogram below:

References

{{Taxonbar, from=Q21127229

Late Cretaceous lepidosaurs of Asia
Campanian life
Monotypic prehistoric reptile genera
Cretaceous South Korea
Fossils of South Korea
Fossil taxa described in 2015