Cimoliasaurus was a plesiosaur that lived during the Late Cretaceous (Maastrichtian) of the eastern United States, with fossils known from New Jersey, North Carolina, and Maryland.

The name Cimoliasaurus magnus was coined by Joseph Leidy for ANSP 9235, one anterior and 12 posterior cervical vertebrae collected in Maastrichtian-aged greensand deposits of the New Egypt and Navesink Formations in Burlington County, New Jersey.

[1] A specimen is also known from coeval limestone deposits of the Peedee Formation in Pender County, North Carolina.

[2] There is also a tentative record from the Maastrichtian-aged Severn Formation in Maryland when in 1988, Colin McEwen discovered a vertebra of a Cimoliasaurus during a school field trip.

[4] Nowadays, Cimoliasaurus is now recognized as being a derived elasmosaurid, effectively making the family name Cimoliasauridae Delair, 1959 a junior synonym of Elasmosauridae.