Liodon is a dubious[1] genus of mosasaur from the Late Cretaceous, known from fragmentary fossils discovered in St James' Pit, England and possibly also the Ouled Abdoun Basin of Morocco.

[2] Though dubious and of uncertain phylogenetic affinities, Liodon was historically a highly important taxon in mosasaur systematics, being one of the genera on which the family Mosasauridae was based.

The other genera initially included in the family were Mosasaurus, Onchosaurus (later recognized to have been a batoid fish), Oplosaurus (a sauropod dinosaur), Macrosaurus (a historical mosasaur "wastebasket taxon") and Geosaurus (a thalattosuchian crocodyliform).

[2] In 1993, Theagarten Lingam-Soliar argued that Liodon was a distinct genus and definable on account of its highly specialized teeth, which Lingham-Soliar believed made it "probably the most efficient in the Mosasauridae for tearing off chunks of soft bodied prey such as fishes and other marine reptiles".

This reassignment followed from the discovery that the L. anceps type specimen was presently missing all tooth material (and as a result all of its supposedly diagnostic features), rendering it a nomen dubium, and from the description of the Prognathodon species P. kianda from Angola.

Over the course of the late 19th and early 20th century, several researchers, including Albert Gaudry in 1892 and Per-Ove Persson in 1959, suggested that L. anceps (but not any of the other species) were congeneric with the tylosaurine genus Hainosaurus, which Russell also believed was a possibility.