Plesiosauroids

Plesiosaurus (Greek: ' ('), near to + ' ('), lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the Early Jurassic. It is known by nearly complete skeletons from the Lias of England. Measuring around long, it is distinguishable by its small head, long and slender neck, broad turtle-like body, a short tail, and two pairs of large, elongated paddles. It lends its name to the order Plesiosauria, of which it is an early, but fairly typical member. It contains only one species, the type, Plesiosaurus dolichodeirus. Other species once assigned to this genus, includi

Plesiosauroidea (; Greek: 'near, close to' and 'lizard') is an extinct clade of carnivorous marine reptiles. They have the snake-like longest neck to body ratio of any reptile. Plesiosauroids are known from the Jurassic and Cretaceous periods. After their discovery, some plesiosauroids were said to have resembled "a snake threaded through the shell of a turtle", although they had no shell.

Microcleidus is an extinct genus of sauropterygian reptile belonging to the Plesiosauroidea. The species has 40 neck vertebrae and a short tail of 28 vertebrae. Fossils of the genus have been found in France, the Posidonia Shale in Germany and Luxembourg, and the Alum Shale Formation of England.

Eretmosaurus (meaning "oar lizard") is an extinct genus of plesiosaur from the Early and Middle Jurassic of England and Russia. Two species are known: E. rugosus and E. dubius.

Eoplesiosaurus is an extinct genus of basal plesiosaur known from the Early Jurassic period (most likely earliest Hettangian stage) of the United Kingdom. It contains a single species, E. antiquior.

Westphaliasaurus is an extinct genus of plesiosaur from Lower Jurassic (Pliensbachian stage) deposits of Westphalia, northwestern Germany. It is known from a nearly complete and articulated skeleton missing the skull and about 38% of the upper neck vertebrae.

Seeleyosaurus is an extinct genus of plesiosaur from Germany and possibly also Russia.

Franconiasaurus (meaning "Franconia reptile") is an extinct genus of basal plesiosauroid plesiosaurs from the Early Jurassic of Germany. The genus contains a single species, F. brevispinus, known from two well-preserved three-dimensional skeletons.

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.

Plesiopharos (derived from the Greek words πλησίος (plesios), "close" and φάρος (pharos), "lighthouse", because its holotype was found in the vicinity of a lighthouse + [from São Pedro de] Moel) is an extinct genus of plesiosaur from the Early Jurassic Coimbra Formation of Portugal. Specifically, it was discovered in São Pedro de Moel, Marinha Grande, from which the type species' binomial name, Plesiopharos moelensis, derives from.

Plesionectes (meaning "near swimmer") is an extinct genus of basal plesiosauroid plesiosaurs known from the Early Jurassic (Toarcian age) Posidonia Shale of Germany. The genus contains a single species, Plesionectes longicollum, known from a well-preserved, nearly complete skeleton.