Jurassic plesiosaurs

left|thumb|Life restoration of Muraenosaurus Cryptoclididae is a family of medium-sized plesiosaurs that existed from the Middle Jurassic to the Early Cretaceous. They had long necks, broad and short skulls and densely packed teeth. They fed on small soft-bodied preys such as small fish and crustaceans. The earliest members of the family appeared during the early Bajocian, and they represented the dominant group of long-necked plesiosaurs during the latter half of the Jurassic.

Sinopliosaurus (meaning "Chinese more lizard") is a dubious genus of pliosauroid plesiosaur. It lived during the Aptian and Albian stages of the Early Cretaceous (disputed Sinopliosaurus remains have been dated to the Toarcian age and were found in the Ziliujing Formation) of the People's Republic of China - its exact age is unknown. The type species, Sinopliosaurus weiyuanensis, was named and described in 1944 by Yang Zhongjian. One species, "S." fusuiensis, was later shown to be based on teeth from a spinosaurid theropod dinosaur which is now known as Siamosaurus. S. weiyuanensis was conside

The Plesiosauridae are a monophyletic family of plesiosaurs named by John Edward Gray in 1825.

Plesiopterys (“plesio” meaning “near,” and “pterys” meaning “wing” or “pterygoid bone”) is an extinct genus of plesiosaur originating from the Posidonienschiefer of Holzmaden, Germany, and lived during the Early Jurassic period. The type and only species is P. wildi, known from two immature specimens with the subadult measuring long. It possesses a unique combination of both primitive and derived characters, and is currently displayed at the State Museum of Natural History and the Hauff Museum, Germany.

Arminisaurus (meaning "lizard of Arminius") is a genus of pliosaurid plesiosaur that lived during the Lower Jurassic in present-day Germany. With Westphaliasaurus and Cryonectes, Arminisaurus is only the third plesiosaurian taxon that was described from the Pliensbachian stage. The holotype and only known specimen is a fragmentary skeleton (about 40 percent complete), comprising an incomplete lower jaw, teeth, vertebrae and elements from the pectoral girdle and the paddles. The animal had an estimated body length of .

Microcleididae is an extinct family of basal plesiosauroid plesiosaurs from the Early Jurassic (middle Sinemurian to late Toarcian stages) of France, Germany, Portugal and the United Kingdom. Currently, the oldest and the most known microcleidid is Eretmosaurus from the middle Sinemurian of the United Kingdom. Microcleididae was formally named and described by Roger B. J. Benson, Mark Evans and Patrick S. Druckenmiller in 2012.