Leninia is an extinct genus of basal ophthalmosaurine ichthyosaur known from the late Early Cretaceous (lower Aptian stage) of western Russia.

The specimen was discovered in 2012, on the banks of the river Volga near the town of Kriushi in a limestone nodule.

it is partially crushed transversely, and nothing further forward than the naris remains, with what seems to be a fairly clean break.

The anterior process and shaft of the jugal are unusually narrow, but the posterior plate is well-developed and extends as high as the middle of the orbit.

The occipital condyle is bulbous, but the floor of the foramen magnum is not well preserved enough to be a diagnostic feature.

Despite this, it still had the very large sclerotic ring and aperture, suggesting that this was one of the most basal characteristics of ophthalmosaurines and that they were all deep-diving, remaining conservative in this ecological niche during the entire time period that they existed.

The absolute size of Leninia's sclerotic ring is among the largest known in ichthyosaurs, with only Baptanodon ('Ophthalmosaurus natans') and the giant Temnodontosaurus exceeding it.

[2] Cladogram based in the phylogenetic analysis of Fischer et al., 2013:[1] Ichthyosaurus communis Stenopterygius quadriscissus Chacaicosaurus cayi Arthropterygius chrisorum Leninia stellans Mollesaurus perialus Ophthalmosaurus icenicus (type species) Baptanodon ("O."

The following cladogram shows a possible phylogenetic position of Leninia in Ophthalmosauridae according to the analysis performed by Zverkov and Jacobs (2020).

[3] 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 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