Undorosaurus is an extinct genus of ophthalmosaurid ichthyosaur known from western Russia, Svalbard, and Poland.^[1][4][2] It was a large ichthyosaur, with the type species measuring 4–6 metres (13–20 ft) long.^[2]

It has been suggested that Cryopterygius be merged into this article. (Discuss) Proposed since December 2023.

Quick Facts Scientific classification, Type species ...

Undorosaurus Temporal range: Late Jurassic,[1] 150.8–145.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N
Recosntructed skeleton
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Ichthyosauria
Family:	†Ophthalmosauridae
Subfamily:	†Platypterygiinae
Genus:	†Undorosaurus Efimov, 1999
Type species
†Undorosaurus gorodischensis (Efimov, 1999)
Other species
†U. nessovi Efimov, 1999 †U. trautscholdi Arkhangelsky & Zverkov, 2014[2] †U. kielanae Tyborowski, 2016[3]
Synonyms
Ophthalmosaurus gorodischensis Maisch & Matzke, 2000 ?Cryopterygius Druckenmiller et al., 2012

Close

Undorosaurus was named by Vladimir M. Efimov in 1999 and the type species is Undorosaurus gorodischensis. The specific name is named after Gorodischi [ru], the type locality of this taxon.^[4] U. trautscholdi is named in honor of the geologist Hermann Trautschold who collected and made the first description of the fossils of the holotype of the species.^[2]

Undorosaurus was first known from the holotype UPM EP-II-20 (527), a partial three-dimensionally preserved skeleton which preserved partial skull. It was collected near the Volga river at Gorodischi from the Epivirgatites nikitini ammonoid zone, dating to the Late Jurassic.^[4] A second species, U. trautscholdi was described by M.S. Arkhangelsky and N.G. Zverkov in 2014 from a partial left forefin found in the locality of Mnyovniki (Mnevniki) [ru], Moscow Oblast.^[2]

Maisch and Matzke (2000) regarded Undorosaurus to be a species of Ophthalmosaurus.^[5] However, Storrs et al. 2000 rejected this synonymy based on the tooth morphology of the specimen.^[6] Chris McGowan and Ryosuke Motani (2003) pointed out two noteworthy differences to Ophthalmosaurus, an incompletely fused ischiopubis and a remarkably strong dentition, and considered Undorosaurus to be a valid genus of ophthalmosaurid.^[7] Undorosaurus's validity is now accepted by most authors, even by Maisch (2010) who originally proposed the synonymy.^[8][9][10]

Zverkov & Efimov (2019) considered the genus Cryopterygius to be a junior synonym of the genus Undorosaurus. The authors considered the type species of the former genus, C. kristiansenae, to be synonymous with Undorosaurus gorodischensis; second species of Cryopterygius, C. kielanae, was tentatively maintained by the authors as a distinct species within the genus Undorosaurus.^[11]

• List of ichthyosaurs
• Timeline of ichthyosaur research