Eurysaurus (meaning "wide lizard") is an extinct genus of plesiosaur, originally classed as a nothosaur, from the Early Jurassic of Echenoz-la-Meline, France, named in 1878. The type material, consisting of a cranium, teeth and five vertebrae, is now lost.^[1] The type species is E. raincourti, and a second species, E. schafferi, was named in 1924 but it has since been absorbed into the unrelated genus Germanosaurus.^[2]

The holotype, first described in 1878 by Albert Gaudry, has since been lost. A new study based essentially on illustrations of the type material by Noè (2001) has considered Eurysaurus a nomen dubium, probably congeneric with the pliosaur Simolestes.^[3] However, due to the stratigraphic difference of the two forms, it is possible that Eurysaurus was a separate genus in its own right.

Gaudry in 1878 originally classified Eurysaurus as a nothosaur.^[1] In 2001, Noè reclassified Eurysaurus as a plesiosaur, possibly belonging to the Pliosauroidea.^[3]

• Timeline of plesiosaur research
• List of plesiosaurs