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Plutoniosaurus; Temporal range: Early Cretaceous, ; ~135–130 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	†Ichthyosauria
Family:	†Ophthalmosauridae
Subfamily:	†Platypterygiinae
Genus:	†Plutoniosaurus; Efimov, 1997
Type species
	†Plutoniosaurus bedengensis; Efimov, 1997
Synonyms
	Platypterygius bedengensis (Efimov, 1997);

Plutoniosaurus is an extinct genus of ophthalmosaurid ichthyosaur of uncertain validity from the Early Cretaceous (late Hauterivian) of the vicinity of Ulyanovsk, European Russia.

Taxonomy

Plutoniosaurus was named by Vladimir Efimov in 1997 based on the holotype specimen UPM 2/740, a partial skeleton containing the skull, the shoulder girdle, forelimbs and vertebrae. The generic name is derived from the Ulyanovsk Regional Young Paleontologists Club that was nicknamed Plutonia. The specific name refers to the village of Novaya Beden’ga, the site of discovery on the right bank of the Volga.

In 1999, Maxim Arkhangel'skii synonymized the genus with Platypterygius,^[1] as did Michael Maisch and Andreas Matzke in 2000.^[2]^: 82 While agreeing with the synonymy, Christopher McGowan and Ryosuke Motani considered P. bedengensis to be a nomen dubium within the genus in 2003, too poorly known to identify as a distinct species.^[3]^: 136 In 2016, Valentin Fischer and colleagues considered the original description was too vague to confidently distinguish the genus and noted that the illustrations did not always match the written description. They thus regarded Plutoniosaurus bedengensis as a species inquirenda, while noting the possibility that it is the same species as the nearly coeval Simbirskiasaurus from the same region.^[4]

Phylogeny

Zverkov and Efimov (2019) recovered Plutoniosaurus in a polytomy with the type species of Platypterygius and Leninia.^[5] The following cladogram shows a possible phylogenetic position of Plutoniosaurus in Ophthalmosauridae according to the analysis performed by Zverkov and Jacobs (2020).^[6]

Ophthalmosauria

Ophthalmosaurinae

Acamptonectes densus

Mollesaurus periallus

	Ophthalmosaurus natans

	Ophthalmosaurus icenicus

Gengasaurus nicosiai

Nannopterygius yasykovi

	Nannopterygius enthekiodon

	Nannopterygius saveljeviensis

	Nannopterygius borealis

Arthropterygius volgensis

Arthropterygius lundi

Arthropterygius thalassonotus

	Arthropterygius hoybergeti

	Arthropterygius chrisorum

Platypterygiinae

Brachypterygius extremus

Aegirosaurus leptospondylus

Muiscasaurus catheti

Leninia stellans

Sveltonectes insolitus

Athabascasaurus bitumineus

Platypterygius americanus

	Acuetzpalin carranzai

	Platypterygius sachicarum

	Caypullisaurus bonapartei

	Grendelius mordax

	Grendelius alekseevi

	Grendelius pseudoscythicus

	Grendelius zhuravlevi

Undorosaurus kielanae

	Undorosaurus nessovi

	Undorosaurus gorodischensis

Platypterygius australis

	Plutoniosaurus bedengensis

	Simbirskiasaurus birjukovi

	Platypterygius hercynicus

	Sisteronia seeleyi

	Platypterygius platydactylus

	Maiaspondylus lindoei

References

^ Storrs, G. W.; Arkhangel'skii, M. S.; Efimov, V. M. (2000). "Mesozoic marine reptiles of Russia and other former Soviet republics". In Benton, M. J.; Shishkin, M. A.; Unwin, D. M.; Kurochkin, E. N. (eds.). The Age of Dinosaurs in Russia and Mongolia. Cambridge: Cambridge University Press. pp. 187–210.
^ Maisch, M. W.; Matzke, A. T. (2000). "The Ichthyosauria". Stuttgarter Beiträge zur Naturkunde, Serie B. 298: 1–159.
^ McGowan, C.; Motani, R. (2003). Sues, H.D. (ed.). Handbook of Paleoherpetology Part 8: Ichthyopterygia. Munich: Verlag Dr. Friedrich Pfeil. ISBN 3899370074.
^ Fischer, V.; Bardet, N.; Benson, R. B. J.; Arkhangelsky, M. S.; Friedman, M. (2016). "Extinction of fish-shaped marine reptiles associated with reduced evolutionary rates and global environmental volatility". Nature Communications. 7: 10825. Bibcode:2016NatCo...710825F. doi:10.1038/ncomms10825. PMC 4786747. PMID 26953824.
^ Zverkov, N. G.; Efimov, V. M. (2019). "Revision of Undorosaurus, a mysterious Late Jurassic ichthyosaur of the Boreal Realm" (PDF). Journal of Systematic Palaeontology. 17 (14): 963–993. Bibcode:2019JSPal..17.1183Z. doi:10.1080/14772019.2018.1515793.
^ Zverkov, N. G.; Jacobs, M. L. (2021) [2020]. "Revision of Nannopterygius (Ichthyosauria: Ophthalmosauridae): reappraisal of the 'inaccessible' holotype resolves a taxonomic tangle and reveals an obscure ophthalmosaurid lineage with a wide distribution". Zoological Journal of the Linnean Society. 191 (1): 228–275. doi:10.1093/zoolinnean/zlaa028.