Plesiosaurs

The Plesiosauria or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia.

Pliosauroidea is an extinct clade of plesiosaurs, known from the latest Triassic to early Late Cretaceous. They are best known for the subclade Thalassophonea, which contained crocodile-like short-necked forms with large heads and massive toothed jaws, commonly known as pliosaurs. More primitive non-thalassophonean pliosauroids resembled plesiosaurs in possessing relatively long necks and smaller heads. They originally included only members of the family Pliosauridae, of the order Plesiosauria, but several other genera and families are now also included, the number and details of which vary ac

Leptocleidus is an extinct genus of plesiosaur, belonging to the family Leptocleididae. It was a small plesiosaur, measuring only up to in length.

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

Leptocleididae is a family of small-sized plesiosaurs that lived during the Early Cretaceous period (early Berriasian to early Albian stage). They had small bodies with small heads and short necks. Leptocleidus and Umoonasaurus had round bodies and triangle-shaped heads. Leptocleidids have been found in what were shallow nearshore, freshwater and brackish habitats. Hilary F. Ketchum and Roger B. J. Benson (2010), transferred Brancasaurus, Kaiwhekea, Nichollssaura and Thililua to this family. However, Ketchum and Benson (2011) reassigned Kaiwhekea and Thililua to their original positions, as an

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.

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thumb|left|Size (green) compared to a human Vectocleidus is an extinct genus of leptocleidid plesiosaurian known from the Early Cretaceous Vectis Formation (late Barremian stage) of Isle of Wight, in the United Kingdom. It contains a single species, Vectocleidus pastorum.

Lindwurmia (named after the Lindwurm) is a rhomaleosaurid plesiosaur from the Early Jurassic of Germany. It contains a single species, Lindwurmia thiuda. It was a small plesiosaur, measuring long.

thumb|Skull dome of Stegoceras (AMNH 5450) showing cross-section thickness

Brimosaurus (meaning "strong lizard") is an extinct genus of plesiosaur from the Late Cretaceous of what is now Arkansas. The type species is Brimosaurus grandis, first named by Joseph Leidy in 1854. The name Brimosaurus is a nomen dubium: the fossils consist of only a few isolated vertebrae, and in 1952 Welles proposed that Brimosaurus was actually synonymous with Cimoliasaurus (which itself is based on dubious material).

Piratosaurus (meaning "pirate lizard") is a dubious genus of plesiosaur possibly belonging to the Polycotylidae that is known exclusively from the type species P. plicatus, named and described by Joseph Leidy in 1865. It is known only from the holotype, USNM V 1000, a tooth, discovered in Late Cretaceous-aged rocks in the Red River basin of Manitoba; at least one researcher erroneously assumed it was found in Minnesota.

denomination given to a Pliosaur fossil of undescribed taxon discovered in Aramberri