This list of plesiosaurs is a comprehensive listing of all genera that have ever been included in the order Plesiosauria, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered invalid, doubtful (nomen dubium), or were not formally published (nomen nudum), as well as junior synonyms of more established names, and genera that are no longer considered plesiosaurs. The list currently includes genera.
Scope and terminology There is no official, canonical list of plesiosaur genera but one of the most thorough attempts can be found on the Plesiosauria section of Mikko Haaramo's Phylogeny Archive;See Haaramo, Plesiosauria. also pertinent is the Plesiosaur Genera section at Adam Stuart Smith's Plesiosaur Directory.See Smith, Plesiosaur Genera.
Naming conventions and terminology follow the International Code of Zoological Nomenclature. Technical terms used include: Junior synonym: A name which describes the same taxon as a previously published name. If two or more genera are formally designated and the type specimens are later assigned to the same genus, the first to be published (in chronological order) is the senior synonym, and all other instances are junior synonyms. Senior synonyms are generally used, except by special decision of the ICZN, but junior synonyms cannot be used again, even if deprecated. Junior synonymy is often subjective, unless the genera described were both based on the same type specimen. Nomen nudum (Latin for "naked name"): A name that has appeared in print but has not yet been formally published by the standards of the ICZN. Nomina nuda (the plural form) are invalid, and are therefore not italicized as a proper generic name would be. If the name is later formally published, that name is no longer a nomen nudum and will be italicized on this list. Often, the formally published name will differ from any nomina nuda that describe the same specimen. In this case, these nomina nuda will be deleted from this list in favor of the published name. Preoccupied name: A name that is formally published, but which has already been used for another taxon. This second use is invalid (as are all subsequent uses) and the name must be replaced. As preoccupied names are not valid generic names, they will also go unitalicized on this list. Nomen dubium (Latin for "dubious name"): A name describing a fossil with no unique diagnostic features. As this can be an extremely subjective and controversial designation, this term is not used on this list.
The list GenusAuthorsYearStatusAgeLocationNotesImages Abyssosaurus Berezin 2011 Valid Early Cretaceous Had a uniquely short, triangular skull with extremely large eye sockets. Shows potential adaptations for specialized deep-diving lifestyle Acostasaurus Gómez-Pérez & Noè 2017 Valid Early Cretaceous Noted for its unusually caniniform dentition compared to other pliosaurids Albertonectes Kubo et al. 2012 Valid Late Cretaceous Had the longest neck of any known plesiosaur, made up of seventy-six vertebrae Alexandronectes Otero et al. 2016 Valid Late Cretaceous The first aristonectine from which a stapes is known Alexeyisaurus Sennikov & Arkhangelsky 2010 Dubious Late Triassic Although originally described as an elasmosaurid plesiosaur, it was suggested to be an undiagnostic sauropterygian taxon by subsequent analyses Alzadasaurus Welles & Bump 1949 Jr. synonym N/A N/A Junior synonym of Styxosaurus Anguanax Cau & Fanti 2015 Valid Late Jurassic Several features of its skull would indicate a diet of soft or small-bodied prey Anningasaura Vincent & Benson 2012 Valid Early Jurassic Known from a partial skeleton belonging to a juvenile animal Apatomerus Williston 1903 Dubious? Early Cretaceous Originally identified as a crocodilian and later reinterpreted as a pterosaur, although it may very likely be a plesiosaur Aphrosaurus Welles 1943 Valid Late Cretaceous Distinguished by the presence of a deepened ventral notch along the centra of its cervical vertebrae Apractocleidus Smellie 1915 Jr. synonym N/A N/A Junior synonym of Cryptoclidus Aptychodon von Reuss 1855 Valid Late Cretaceous Some studies suggest this genus may be a potential junior synonym of Polyptychodon Archaeonectrus Novozhilov 1964 Valid Early Jurassic Originally mistakenly believed to be a species of Plesiosaurus Argentinonectes Novas et al. 2026 Valid Late Cretaceous Several shark teeth were found in association with the holotype Aristonectes Cabrera 1941 Valid Late Cretaceous Antarctica This genus would have migrated regularly between Patagonia and Antarctica as implied by its fossil record Arminisaurus Sachs & Kear 2017 Valid Early Jurassic Shares some features of its skeleton with leptocleidian plesiosauroids Attenborosaurus Bakker 1993 Valid Early Jurassic Named in honor of British broadcaster and naturalist David Attenborough Atychodracon Smith 2015 Valid Late Triassic to Early Jurassic Has been assigned to four different genera before its formal description Avalonnectes Benson, Evans & Druckenmiller 2012 Valid Early Jurassic One of the oldest plesiosaurs known to date Bathyspondylus Delair 1982 Valid Late Jurassic Possesses an unusual mix of pliosauroid and plesiosauroid features Bishanopliosaurus Dong 1980 Valid Early Jurassic to Middle Jurassic Could be distinguished by the bifurcated ribs of its sacrum Borealonectes Sato & Wu 2008 Valid Middle Jurassic One of the few North American plesiosaurs that lived during the Jurassic Boyacasaurus Benavides-Cabra et al. 2025 Valid Early Cretaceous Known from two specimens found in association with ammonites Brachauchenius Williston 1903 Valid Late Cretaceous Several pliosaurid specimens of same age had been referred to this genus, although they were either renamed as new taxa or considered dubious Brancasaurus Wegner 1914 Valid Early Cretaceous Its cervical vertebrae are noted for having shark fin-shaped neural spines Brimosaurus Leidy 1854 Dubious Late Cretaceous May be synonymous with Cimoliasaurus Callawayasaurus Carpenter 1999 Valid Early Cretaceous Has no pectoral bars, a trait shared with Terminonatator Cardiocorax Araújo et al. 2015 Valid Late Cretaceous The morphology of its scapula suggests a relatively unique swimming style for this genus Ceraunosaurus Thurmond 1968 Jr. synonym N/A N/A Junior synonym of Trinacromerum Chubutinectes O'Gorman et al. 2023 Valid Late Cretaceous Larger than the contemporary Kawanectes due to its marine habitat Cimoliasaurus Leidy 1851 Valid Late Cretaceous Discovered in sediments that superficially resemble the chalk deposits found in the Western Interior Seaway Colymbosaurus Seeley 1874 Valid Middle Jurassic to Late Jurassic The holotype humerus was originally misidentified as a femur Crymocetus Cope 1869 Dubious Late Cretaceous Today seen as an indeterminate plesiosaur. Only known from a single vertebra Cryonectes Vincent, Bardet & Mattioli 2012 Valid Early Jurassic Possessed a relatively elongated snout Cryptoclidus Seeley 1892 Valid Middle Jurassic to Late Jurassic Would have preyed on small, soft-bodied animals as indicated by the delicate build of its skull and teeth Discosaurus Leidy 1851 Valid Late Cretaceous Has been argued to be the same taxon as Elasmosaurus Djupedalia Knutsen, Druckenmiller & Hurum 2012 Valid Late Jurassic Named after former Minister of Education and Research Øystein Djupedal Dolichorhynchops Williston 1902 Valid Late Cretaceous Described two years after its discovery Dravidosaurus Yadagiri & Ayyasami 1979 Dubious Late Cretaceous Suggested to be either an ornithischian (potentially stegosaurian) dinosaur or a plesiosaur Eardasaurus Ketchum & Benson 2022 Valid Middle Jurassic Had prominent enamel ridges in its teeth, which would indicate a diet of large prey Edgarosaurus Druckenmiller 2002 Valid Early Cretaceous One of the first polycotylids to become native to the Western Interior Seaway Eiectus Noè & Gómez-Pérez 2021 Valid? Early Cretaceous Potentially synonymous with Kronosaurus Elasmosaurus Cope 1868 Valid Late Cretaceous Originally erroneously reconstructed with its skull placed at the end of its tail Embaphias Cope 1894 Dubious Late Cretaceous Based on three cervical vertebrae Eoplesiosaurus Benson, Evans & Druckenmiller 2012 Valid Early Jurassic May have been the basalmost known member of the Plesiosauroidea EopolycotylusPLESIOSAURS FROM THE UPPER CRETACEOUS (CENOMANIAN–TURONIAN) TROPIC SHALE OF SOUTHERN UTAH, PART 2: POLYCOTYLIDAE