Plutoniosaurus

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, as did Michael Maisch and Andreas Matzke in 2000. 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. 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.

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