Pliosauroidea is an extinct clade of plesiosaurs, known from the earliest Jurassic 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 according to the classification used.
Liopleurodon is an extinct genus of carnivorous pliosaurid pliosaurs that lived from the Callovian stage of the Middle Jurassic to the Kimmeridgian stage of the Late Jurassic period. The type species is L. ferox, which is probably the only valid species. Some studies also include the second species L. pachydeirus, but this latter is considered as a probable junior synonym of L. ferox due to its lack of viable diagnosis. As the holotype specimen of L. ferox consists of a single tooth preserving questionable distinctive features, recent studies therefore recommend the necessary identification of a neotype in order to preserve the validity of the genus. Numerous fossil specimens attributed to Liopleurodon, even including numerous skeletons, have been discovered in Europe, Russia, and Mexico. Other additional species were even proposed, but these are currently seen as coming from other pliosaurid genera.
Elasmosauridae is an extinct family of plesiosaurs, often called elasmosaurs. They had the longest necks of the plesiosaurs and existed from the Hauterivian to the Maastrichtian stages of the Cretaceous, and represented one of the two groups of plesiosaurs present at the end of the Cretaceous alongside Polycotylidae.
Peloneustes is a genus of pliosaurid plesiosaur from the Middle Jurassic of England. Its remains are known from the Peterborough Member of the Oxford Clay Formation, which is Callovian in age. It was originally described as a species of Plesiosaurus by palaeontologist Harry Govier Seeley in 1869, before being given its own genus by naturalist Richard Lydekker in 1889. While many species have been assigned to Peloneustes, P. philarchus is currently the only one still considered valid, with the others moved to different genera, considered nomina dubia, or synonymised with P. philarchus. Some of the material formerly assigned to P. evansi have since been reassigned to "Pliosaurus" andrewsi. Peloneustes is known from many specimens, including some very complete material.
Rhomaleosaurus is an extinct genus of Early Jurassic rhomaleosaurid pliosauroid known from Northamptonshire and from Yorkshire of the United Kingdom. It was first named by Harry Seeley in 1874 and the type species is Rhomaleosaurus cramptoni. It was one of the earliest large marine reptile predators which hunted in the seas of Mesozoic era, measuring about 7 metres (23 ft) long. Like other pliosaurs, Rhomaleosaurus fed on ichthyosaurs, ammonites and other plesiosaurs.
Umoonasaurus is an extinct genus of plesiosaur belonging to the family Leptocleididae. This genus lived approximately 115 million years ago during the Early Cretaceous period, in shallow seas covering parts of what is now Australia. It was a relatively small animal around 2.5 metres (8.2 ft) long. An identifying trait of Umoonasaurus is the presence of three crest-ridges on its skull.
Trinacromerum is an extinct genus of sauropterygian reptile, a member of the polycotylid plesiosaurs. It contains two species, T. bentonianum and T. kirki. Specimens have been discovered in the Late Cretaceous fossil deposits of what is now modern Kansas and Manitoba.
Polycotylidae is a family of plesiosaurs from the Cretaceous, a sister group to Leptocleididae. They are known as false pliosaurs. Polycotylids first appeared during the Albian stage of the Early Cretaceous, before becoming abundant and widespread during the early Late Cretaceous. Several species survived into the final stage of the Cretaceous, the early Maastrichtian around 72 million years ago. The possible latest surviving member Rarosaurus from the late Maastrichtian is more likely a crocodylomorph.
Dolichorhynchops is an extinct genus of polycotylid plesiosaur from the Late Cretaceous of North America, containing the species D. osborni and D. herschelensis, with two previous species having been assigned to new genera. Definitive specimens of D. osborni have been found in the late Coniacian to early Campanian rocks, while those of D. herschelensis have been found in the late Campanian to early Maastrichtian rocks. Dolichorhynchops was a prehistoric marine reptile measuring around 3 metres (9.8 ft) long. Its Greek generic name means "long-nosed face".
Thalassiodracon (tha-LAS-ee-o-DRAY-kon) is an extinct genus of plesiosauroid from the Pliosauridae that was alive during the Late Triassic-Early Jurassic (Rhaetian-Hettangian) and is known exclusively from the Lower Lias of England. The type and only species, is Thalassiodracon (Plesiosaurus) hawkinsii.
Leptocleidus is an extinct genus of plesiosaur, belonging to the family Leptocleididae. It was a small plesiosaur, measuring only up to 3 m (9.8 ft).
Augustasaurus is an extinct genus of sauropterygians that lived during the Anisian stage of the Middle Triassic in what is now North America. Only one species is known, A. hagdorni, described in 1997 from fossils discovered in the Favret Formation, Nevada, USA.
Hauffiosaurus is an extinct genus of Early Jurassic pliosaurid plesiosaur known from Holzmaden of Germany and from Yorkshire of the United Kingdom. It was first named by Frank Robin O’Keefe in 2001 and the type species is Hauffiosaurus zanoni. In 2011, two additional species were assigned to this genus: H. longirostris and H. tomistomimus.
Bobosaurus is an extinct genus of sauropterygian reptile related to plesiosaurs. It is based on the holotype MFSN 27285, a partial skeleton found in Early Carnian-age rocks of the Rio del Lago Formation, northeastern Italy. Bobosaurus was named in 2006 by Fabio M. Dalla Vecchia and the type species is B. forojuliensis. It may be a pistosaurid, or closer to Plesiosauria. A recent cladistic analysis found it to be a pistosaur. It was relatively large animal, with more than 3 m (9.8 ft) in length.
Seeleyosaurus is an extinct genus of plesiosaur from Germany and possibly also Russia.
Microcleididae is an extinct family of basal plesiosauroid plesiosaurs from the Early Jurassic 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.
This timeline of plesiosaur research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, taxonomic revisions, and cultural portrayals of plesiosaurs, an order of marine reptiles that flourished during the Mesozoic Era. The first scientifically documented plesiosaur fossils were discovered during the early 19th century by Mary Anning. Plesiosaurs were actually discovered and described before dinosaurs. They were also among the first animals to be featured in artistic reconstructions of the ancient world, and therefore among the earliest prehistoric creatures to attract the attention of the lay public. Plesiosaurs were originally thought to be a kind of primitive transitional form between marine life and terrestrial reptiles. However, now plesiosaurs are recognized as highly derived marine reptiles descended from terrestrial ancestors.
Arminisaurus 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, comprising an incomplete lower jaw, teeth, vertebrae and elements from the pectoral girdle and the paddles. The animal had an estimated body length of 3–4 metres (9.8–13.1 ft).
"Pliosaurus" andrewsi is an extinct species of pliosaurid plesiosaurs that lived during the Callovian stage of the Middle Jurassic, in what is now England. The only known fossils of this taxon were discovered in the Peterborough Member of the Oxford Clay Formation. Other attributed specimens have been discovered in various corners of Eurasia, but these are currently seen as indeterminate or coming from other taxa. The taxonomic history of this animal is quite complex, because several of its fossils were attributed to different genera of pliosaurids, before being concretely named and described in 1960 by Lambert Beverly Tarlo as a species of Pliosaurus. However, although the taxon was found to be valid, subsequent revisions found that it is not part of this genus, and therefore a taxonomic revision must be carried out on this species.
