Otschevia Efimov, 1998 Grendelius is a genus of platypterygiine ophthalmosaurid ichthyosaur from the Late Jurassic (Kimmeridgian-Tithonian) of the UK and European Russia.

[1] The type species, Grendelius mordax, was described in 1976 on the basis of CAMSM J.68516, a complete skull with associated postcranial elements from the Kimmeridge Clay of England.

[9] While McGowan and Motani (2003) considered these Russian taxa to be junior synonyms of B. extremus,[4] Maisch (2010) retained them, and B. mordax, as separate species.

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

[11] 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