The oldest Jurassic marine pleurodire is reported from the Jagua Formation in western Cuba. These remains are from levels of middle and late Oxfordian age. This turtle represents a new genus and species, Caribemys oxfordiensis. A phylogenetic hypothesis is proposed, whereby Caribemys is considered to be the sister group of Notoemys Cattoi and Freiberg, 1961, plus the Eupleurodira Gaffney and Meylan, 1988. The occurrence of Caribemys oxfordiensis n. gen. and sp. in the Jagua Formation along with plesiosauroids, pliosauroids, ophthalmosaurian ichthyosaurs, and metriorhynchid crocodiles, strongly suggests that during the Oxfordian a marine seaway was present in the Caribbean, connecting the western Tethys with the Pacific Ocean.