Asprosaurus

{{Speciesbox

| fossil_range = Campanian {{fossilrange|81|refs={{cite journal|year=2017|last1=Kim|first1=J.K.|last2=Kwon|first2=Y.E.|last3=Lee|first3=S.G.|last4=Kim|first4=C.Y.|last5=Kim|first5=J.G.|last6=Huh|first6=M.|last7=Lee|first7=E.|last8=Kim|first8=Y.J.|title=Correlative microscopy of the constituents of a dinosaur rib fossil and hosting mudstone: Implications on diagenesis and fossil preservation|journal=PLOS One|volume=13|issue=3|pages=e0195421|doi=10.1371/journal.pone.0186600|doi-access=free|pmc=5648225}}}}

| image = File:Jugal postorbital process of Asprosaurus.jpg

| image_caption = Jugal postorbital process of Asprosaurus

| taxon = Asprosaurus bibongriensis

| parent_authority = Park, Evans & Huh, 2015

| authority = Park, Evans & Huh, 2015

| display_parents = 2

}}

Asprosaurus ({{lit|white lizard}}) 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.{{cite journal|last1=Park|first1=Jin-Young|last2=Evans|first2=Susan E.|last3=Huh|first3=Min|year=2015|title=The first lizard fossil (Reptilia: Squamata) from the Mesozoic of South Korea|journal=Cretaceous Research|volume=55|pages=292–302|doi=10.1016/j.cretres.2015.03.001}}

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.{{cite journal|last1=Park|first1=Jin-Young|year=2016|script-title=ko:보성군 비봉리 공룡알 화석지에서 발견된 새로운 무족도마뱀류 (Anguimorpha) 두개골 화석에 대한 기재|trans-title=Description of a new Anguimorpha lizard skull fossil from the Boseong Bibong-ri Dinosaur egg site, South Korea|journal=Korean Journal of Herpetology|volume=7|issue=1|pages=15–22|issn=2005-9019|url=https://www.earticle.net/Article/A267372|language=ko}}

Description

Asprosaurus has an estimated skull length of {{convert|18|-|20|cm|abbr=on}}. It is probably larger than Chianghsia,{{Cite journal|last1=Cabezuelo Hernández |first1=T. |last2=Bolet |first2=A. |last3=Torices |first3=A. |last4=Pérez-García |first4=A. |year=2021 |title=Identification of a large anguimorph lizard (Reptilia, Squamata) by an articulated hindlimb from the upper Maastrichtian (Upper Cretaceous) of Basturs-1 (Lleida, Spain) |journal=Cretaceous Research |volume=131 |pages=Article 105094 |doi=10.1016/j.cretres.2021.105094|issn=0195-6671 |s2cid=244352137 |doi-access=free }} whose skull length is estimated up to {{cvt|17.5|-|18|cm|in}} in total and the snout-vent length around {{cvt|1|-|1.25|m}}.{{Cite journal | last1 = Mo | first1 = J. Y. | last2 = Xu | first2 = X. | last3 = Evans | first3 = S. E. | doi = 10.1080/14772019.2011.588254 | url= https://www.researchgate.net/publication/228117628_A_large_predatory_lizard_Platynota_Squamata_from_the_Late_Cretaceous_of_South_China | title = A large predatory lizard (Platynota, Squamata) from the Late Cretaceous of South China | journal = Journal of Systematic Palaeontology | volume = 10 | issue = 2 | pages = 333 | year = 2012 | s2cid = 85682211 }} The jugal of Asprosaurus preserves an angulated orbital margin, but lacks osteoderms and differs in shape from that of the Chinese monstersaurian Zhongyuanxi.{{cite journal |last1=Xu |first1=L. |last2=Dong |first2=L. |last3=Gao |first3=D. |last4=Li |first4=Y. |last5=Wu |first5=Y. |last6=Chang |first6=F. |last7=Li |first7=J. |last8=Evans |first8=S. |title=A new anguimorph lizard from the Upper Cretaceous of Henan Province, China |journal=Journal of Systematic Palaeontology |year=2025 |volume=23 |issue=1 |at=2470790 |doi=10.1080/14772019.2025.2470790 }}

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.{{cite book|author1=Augusta, B.G.|author2=Zaher, H.|author3=Polcyn, M.J.|author4=Fiorillo, A.R.|author5=Jacobs, L.L.|chapter=A Review of Non-Mosasaurid (Dolichosaur and Aigialosaur) Mosasaurians and Their Relationships to Snakes|title=The Origin and Early Evolutionary History of Snakes|year=2022|publisher=Cambridge University Press|editor1=Gower, D.J.|editor2=Zaher, H.|pages=157–179|doi=10.1017/9781108938891|isbn=9781108938891}}

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:{{Cite journal |last1=Woolley |first1=C. Henrik |last2=Sertich |first2=Joseph J. W. |last3=Melstrom |first3=Keegan M. |last4=Irmis |first4=Randall B. |last5=Smith |first5=Nathan D. |date=2025-06-18 |title=New monstersaur specimens from the Kaiparowits Formation of Utah reveal unexpected richness of large-bodied lizards in Late Cretaceous North America |url= |journal=Royal Society Open Science |language=en |volume=12 |issue=6 |doi=10.1098/rsos.250435 |issn=2054-5703 |doi-access=free}}