Scanisaurus is a dubious genus of plesiosaur that lived in what is now Sweden and Russia during the Campanian stage of the Late Cretaceous period.

Due to the limited type material and the lack of diagnostic features in the Swedish fossils confidently separating Scanisaurus from other Late Cretaceous elasmosaurids, the genus is of questionable validity, though it continues to be used in practice.

In 1911, Russian paleontologist Nikolay Bogolyubov described a Late Cretaceous posterior cervical (neck) vertebral centrum discovered near Orenburg, Russia.

Furthermore, Persson noted several differences between Bogolyubov's centrum and the Swedish material and the fossils of C. magnus, and considered C. nazarowi distinct enough to warrant being placed in a separate genus.

[4] Persson noted that the Swedish fossils were the same species "with a fairly great degree of probability" and provisionally designated them as S. cf.

nazarowi, consisting of vertebrae, teeth and limb bones, was more complete than the material referred to Elasmosaurus, it was deemed to lack any diagnostic features with which it could be differentiated from other Late Cretaceous elasmosaurids.

[7] Though Scanisaurus for this reason is typically no longer considered a valid taxon (constituting a nomen dubium), the name continues to be used in practice.

[11] Based on the size of its fossils and comparisons with the proportions of other plesiosaurs, Scanisaurus probably reached 4–5 meters (13–16 ft) in length.

With this in mind, Persson suggested that Scanisaurus could be a representative of a new family of Late Cretaceous plesiosaurs, possibly a group intermediate between pliosaurs such as the polycotylids and elasmosaurids.

[10] In 1963, Persson also referred Aristonectes to the Cimoliasauridae on account of perceived close resemblances with fossil material of Cimoliasaurus and Scanisaurus in the length-width ratio of the cervical centra.

[17][18] Kear and colleagues drew this conclusion from the fact that elasmosaurid teeth were both structurally fragile and took more time to replace than the teeth of other reptiles, meaning that elasmosaurids such as Scanisaurus would probably have kept to easily subdued prey to minimize the potential for damage, making them ecologically optimized towards middle trophic level aquatic predation.

Stomach content from other plesiosaurs has revealed a wide variety of prey, including bottom-dwelling invertebrates (i.e. gastropods and bivalves), fish, pterosaurs and ammonites.

[6][8] During the Campanian, the Kristianstad Basin was a subtropical to temperate shallow inland sea home to a diverse marine fauna characteristic of shallow marine life of an inner shelf community and included abundant algae, brachiopods, bryozoans, molluscs (including bivalves, gastropods, belemnites and the ammonites), sea urchins, serpulids, decapods and sponges.