Elasmosaurus is a genus of plesiosaur with an extremely long neck that lived in the Late Cretaceous. It was about 14 m (46 ft) in length and weighed over 2,000 kg (2.2 tons), making it the second longest plesiosaur. It had a large body and four flippers for limbs. More than half of its length was neck, which had more than 70 vertebrae, more than any other animal. It had a relatively small head with sharp teeth.

Futabasaurus is a genus of plesiosaur from the Late Cretaceous of Fukushima, Japan. Described and named in 2006, it was assigned to the family Elasmosauridae.

Hydrotherosaurus ("Water beast lizard") is an extinct genus of elasmosaurid plesiosaur from the Upper Cretaceous (Maastrichtian) of Fresno County, California, measuring up to 13 m in length.

Macroplata is an extinct genus of Early Jurassic pliosaur, which grew up to 4.5 metres (15 ft) in length. Like other pliosaurs, Macroplata probably lived on a diet of fish, using its sharp needle-like teeth to catch prey. Its shoulder bones were fairly large, indicating a powerful forward stroke for fast swimming. Macroplata also had a relatively long neck, twice the length of the skull, in contrast to later pliosaurs.

Muraenosaurus ("Moray eel lizard") is an extinct genus of sauropterygian reptile, from the Middle Jurassic of Europe. Fossils have been found in England and France. Muraenosaurus grewing to around 6 metres (20 ft) long, with around half of that length being taken up by the animal's neck, which possessed 44 vertebrae. Behind the neck, Muraenosaurus had a short, relatively inflexible body and powerful flippers. The head was remarkably small compared to the overall size of the animal, being only around 37 centimetres (15 in) long.

Nothosaurus is an extinct genus of sauropterygian reptile from the Triassic period, approximately 240-210 million years ago, with fossils being distributed from North Africa and Europe to China. It is the best known member of the nothosaur order. Its name means False lizard.

Plesiosaurus lived during the early part of the Jurassic Period, and is known by nearly complete skeletons from the Lias of England and Germany. It was distinguished 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.