Genera

Abyssosaurus is a derived cryptoclidid plesiosaur from the Upper Hauterivian (Lower Cretaceous) of the Menya River, Chuvashia, Russia. It was named and described in 2011 by Alexander Yu Berezin (Berezin 2011). A partial skull associated with the holotype specimen (MChEIO, no. PM/1) was not described in the original 2011 paper but was discovered later in […]

Albertonectes is a very long-necked elasmosaurid from the Late Cretaceous of Alberta, Canada. The holotype specimen (TMP 2007.0110001) consists of an almost complete skeleton lacking a skull (Kubo et al. 2012). The neck contains 76 cervical vertebrae, which is a unique character of Albertonectes vanderveldei and the highest number of neck vertebrae known for any […]

Alexeyisaurus is the stratigraphically oldest named possible plesiosaur. It was named and described by Sennikov and Arkhangelsky (2010) as an elasmosaurid plesiosaur from the Late Triassic of Franz Josef Land, Russia. This would be highly unusual because the oldest definitive elasmosaurid plesiosaurs are otherwise restricted to the Cretaceous Period. The holotype material of Alexeyisaurus is a […]

Anguanax is the first articulated plesiosaur ever found in Italy. It is a basal thalassophonean pliosaur from the Late Jurassic (middle Oxfordian). The type and only known specimen (MPPL 18797) of Anguanax was originally described as an indeterminate pliosaurid (Cau and Fanti 2014), but was subsequently named after reanalysis by the same authors the following […]

Anningasaura is a basal plesiosaur from the Lower Jurassic of Lyme Regis, UK, known from a single three-dimensionally preserved skull. The specimen, NHMUK OR49202, was originally described and figured by Andrews (1896), who referred it to ‘Plesiosaurus‘ macrocephalus. It was redescribed and named as the holotype of Anningasaura lymense by Vincent and Benson (2012). The […]

The genus and species ‘Apractocleidus teretipes‘ was erected by Smellie (1916). Smellie (1915) provided a preliminary account of the specimen before he named it. The specimen is now regarded as an old-adult individual of Cryptoclidus. The taxon ‘Apractocleidus‘ is therefore considered a junior synonym of Cryptoclidus. The specimen was collected by Alfred Leeds and acquired […]

The genus Archaeonectrus was proposed by Novozhilov (1964) for ‘Plesiosaurus’ rostratus, a species named by Owen (1865). By modern standards, Owen’s (1865) original description is rather inadequate. One notable characteristic of Archaeonectrus rostratus is the relatively small size of the limbs relative to its body. It has been classified as a pliosauroid, sometimes within the […]

The mysterious plesiosaur Aristonectes is notable for its mouthful of pin-like teeth. A special feeding guild, the ‘trap guild’, has been proposed to accommodate Aristonectes and other plesiosaurs with similar dentition (Chatterjee and Small 1989) such as Cryptoclidus, Kimmerosaurus, and Kaiwhekea. These plesiosaurs may have fed in a similar manner to the extant crabeater seal, […]

Attenborosaurus is an unusual plesiosaur because it combines a long neck with a relatively large head. It is classified as a pliosaur in some classifications, but some phylogenies place it in a more basal position. The genus was introduced for ‘Plesiosaurus’ conybeari, a species originally described by Sollas (1881). Bob Bakker coined the new genus […]

The genus Atychodracon was erected by Smith (2015) to accommodate ‘Rhomaleosaurus’ megacephalus, because it is generically separarate from Rhomaleosaurus sensu stricto (Smith and Dyke 2008). A. megacephalus is closely related to Eurycleidus and some authors have regarded A. megacephalus as a distinct species of Eurycleidus. The holotype specimen of A. megacephalus (BRSMG Cb 2335) was […]

Avalonnectes is a small-bodied basal rhomaleosaurid. Avalonnectes was named by Benson, Evans and Druckenmiller (2012) for a partial skeleton including the rear part of the skull from the lowermost Jurassic of Street, Somerset, UK. The specimen (NHMUK PV OR 14550) was previously referred to Thalassiodracon hawkinsii and is one of many historical plesiosaur skeletons preserved […]

Bishanopliosaurus is the most complete plesiosaur known from the Jurassic of Asia (Sato et al. 2003). The holotype specimen of the type species, B. youngi, is a partial postcranial skeleton of a juvenile individual from the Dongyuemiao Member of the Ziliujing Formation (Lower or Mid Jurassic) of Bishan County, Chongqing, China. It was first described […]

Bobosaurus shares many characteristics with plesiosaurs and is one of a number of recently discovered derived sauropterygians that bridge the gap between basal sauropterygians and plesiosaurians. The name honours the person who found the skeleton, Mr Roberto “Bobo” Rigo (Dalla Vecchia 2006).

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Colymbosaurus is a colymbosaurine (derived cryptoclidid) from the Late Jurassic of the UK and Svalbard, Norway. Two valid species are known, C. megadeirus from the UK, and C. svalbardensis from Svalbard, Norway. The genus is known from the Kimmeridgian, Tithonian, and possibly early Berriasian (Late Jurassic–possibly Early Cretaceous). Benson and Bowdler (2014) revised the genus […]

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Cryptoclidus, often wrongly spelled ‘Cryptocleidus’ after Andrews (1909), is a moderately sized plesiosaur with adults about four metres long (Brown 1981). It is known from a large number of individual specimens from the Oxford Clay Formation. Fossils of Cryptoclidus are relatively common, and provide a complete ontogenetic sequence from very young to old adult individuals. […]

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Williston (1903) originally diagnosed Dolichorhynchops as follows: “Head elongate, the facial region much attenuated; teeth nearly uniform in size, small; prefrontals and postfrontal bones not joined; parietals extending into a high crest; supraocciptial bones separated; internal nares small, included between the vomer and the palatine only; palatines broadly separated throughout; a large vacuity between the […]

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Edgarosaurus is a basal polycotylid (Druckenmiller 2002) from the Thermopolis Shale

Elasmosaurus is one of the most widely recognised plesiosaur names and has become a stereotype for all elasmosaurids. However, it is relatively poorly known. The type and only known specimen of Elasmosaurus platyurus (ANSP 10081) includes the tip of the snout, occipital condyle, and the majority of the vertebral column. It is from the Sharon […]

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The genus Eretmosaurus was erected for ‘Plesiosaurus’ rugosus by Seeley (1874). Eretmosaurus is a rogue taxon in cladistic analyses and researchers have been in disagreement about its taxonomic affinity. Eretmosaurus has been included in several different families: the Rhomaleosauridae based on the anatomy of its girdles (Persson 1963); the Pliosauridae (Brown 1981), the Elasmosauridae (Bardet 1995, […]

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‘Gronausaurus‘ was named in 2013 (Hampe 2013). It is now regarded as a junior synonym of Brancasaurus (Sachs et al. 2016). Under construction

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Hauffiosaurus is a basal pliosaurid known from the Lower Jurassic (Toarcian) of the UK and Germany. Hauffiosaurus is a medium to large sized plesiosaur (H. zanoni = 3.4 m, H. tomistomimus, 4.23 m, H. longirostris = 4.83 m) (Smith and Lomax 2019), with a relatively long neck for a pliosaur, and an elongate narrow snout. […]

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Hydrotherosaurus is a long-necked elasmosaurid from California, USA. It is represented by one of the most complete elasmosaurid skeletons ever discovered, so Hydrotherosaurus is one of the best known members of this family. The almost complete type skeleton of Hydrotherosaurus was discovered in the Panoche Hills by Mr. Frank C. Paiva in 1937, and was […]

Kaiwhekea, also known as the ‘Shag Point Plesiosaur’, was classified as a cryptoclidid by Cruickshank and Fordyce (2002). More recent classifications regard it as an aristonectid. It has an unusually large number of small needle-like teeth and a shortened snout, much like the closely related Aristonectes. Kaiwhekea katiki is the type and only species.

Kimmerosaurus is a poorly known cryptoclidid plesiosaur known only from skull and neck material (Brown 1981, Brown et al. 1986). It differs from other plesiosaurs in the large number of needle-like teeth in its jaws, and in the form of its teeth, which are completely smooth and lack the longitidinal ridges present in other plesiosaurs. […]

Due to its large size and ferocious appearance, Kronosaurus is one of the most famous plesiosaurs. The iconic skeleton referred to Kronosaurus on display in the Museum of Comparative Zoology in Harvard is nicknamed ‘plasterosaurus’ because so much of it is reconstructed in plaster. About a third of the skeleton is plaster and there are […]

Lower Cretaceous plesiosaurs are rare, so Leptocleidus is important because it fills a gap in the fossil record of plesiosaurians. Leptocleidus was once considered to be a late surviving member of the family Rhomaleosauridae but it has recently been reidentified as a close relative of polycotylids. The fossils of all known species of Leptocleidus were […]

Libonectes was erected for ‘Elasmosaurus morgani’. The pectoral girdle and a forelimb of the holotype are figured (most recently by Welles 1962, fig. 12) but now lost (Carpenter 1999). Libonectes morgani (Welles 1949) is the type and only species. Type material of L. morgani (SMUSMP 69120) consists of a skull, cervical vertebrae and gastralia, from the […]

Liopleurodon is a pliosaur that hardly needs introduction since appearing as the villain in the BBC’s ‘Walking with Dinosaurs’ TV series. This led to popular misconceptions about the size of Liopleurodon, which is known to have reached adult sizes in the region of seven metres long, nowhere near the gargantuan 25m estimate proposed by the […]

Lusonectes is a poorly known microcleidid the Toarcian (Lower Jurassic) of Portugal. It is known from a single holotype specimen (MG33), a partial skull in the Museu Geológico, Lisbon, Portugal. It was described and named by Smith et al. (2012) as the first diagnostic plesiosaur species from Portugal, and the westernmost occurrence of a plesiosaur […]

Macroplata is a rhomaleosaurid plesiosaur from the Lower Jurassic of Warwickshire, UK. Macroplata was named and briefly described by Swinton (1930a) based on a single skeleton from Harbury, Warwickshire, and the skeleton was redescribed in detail by Ketchum and Smith (2010). White (1940) referred the species Plesiosaurus longirostris to Macroplata, and this species has been […]

M. coccai (Gasparini 1997) type material: MOZ 4386 V articulated skull and mandible, atlas-axis and first cervical vertebrae. From the upper part of the Los Molles Formation, Cuyo Group, Emileia giebeli and Emileia multiformis subzone.

Marmornectes is a pliosaur with a long and narrow snout from the Oxford Clay. It was described and named by Ketchum and Benson (2011a). The type and only specimen (BEDFM 1999.201) comprises a substantially complete skeleton including a partial skull. Marmornectes is similar to Peloneustes but possesses some basal characters that were lost in Peloneustes […]

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M. victor was originally described and figured by Fraas (1910). Historically, M. victor has been regarded as a species of Rhomaleosaurus and is often associated in the literature under the defunct name ‘Thaumatosaurus’. See my article about this history of ‘Thaumatosaurus‘ here. Smith and Vincent (2010) identified M. victor as generically distinct from Rhomaleosaurus and erected […]

Microcleidus is a medium (4.27 m) to large (5.03 m) plesiosauroid with a small head and a long neck containing 38–39 cervical vertebrae. Watson (1909) erected Microcleidus to accommodate fossil material belonging to ‘P.’ homalospondylus and ‘P.’ macropterus (Watson 1911). Both species were considered valid by Seeley (1865), Blake (1876) and Watson (1911) on the basis of […]

Monquirasaurus is a giant pliosaurid from Colombia, South America. Originally named by Hampe (1992) as a species of Kronosaurus (K. boyacensis), the skeleton was later allocated to the new genus Monquirasaurus by Noè and Gómez-Pérez (2021). The genus name derives from ‘Monquira’, the administrative division in which the holotype was discovered.

The taxon was originally named ‘Turneria seymourensis‘ by Chatterjee and Small (1989) but this genus was preoccupied and so Chatterjee and Creisler (1994) later revised the name to Morturneria seymourensis. The holotype specimen is TTU P 9219, an incomplete skull and mandible plus associated cervical vertebrae, from the Lopez de Bertodano Formation of Seymour Island, […]

Brown (1981) diagnosed Muraenosaurus as follows: “Plesiosauroids in which the teeth are ornamented with many longitudinal ridges; the dentary bears 19 to 22 teeth on each ramus; the premaxillae bear 5 teeth each, of which the 1st and 5th are small, and the 2nd to 4th are large; the most anterior maxilliary tooth (6th upper […]

Nakonanectes is a small elasmosaurid plesiosaur from the Bearpaw Shale of Montana, USA. It is known from a single moderately complete specimen including a particularly fine skull. It has a relatively short neck for an elasmosaur consisting of ‘only’ 39-42 neck vertebrae. However, 16–19 of the neck vertebrae were lost in a “heavy spring runoff […]

‘Occitanosaurus’ was described by Sciau et al. (1990) and Bardet et al. (1999). The genus name was erected for ‘Plesiosaurus’ tournemirensis by Bardet et al. (1999). The taxon was originally regarded as an early elasmosaurid but is now considered a member of the Microcleididae. ‘Occitanosaurus’ was approximately 3.9 meters long. The type material (MMM J. […]

The type skeleton of ‘Ogmodirus’ was collected in 1909 by C. Boyce from the upper Greenhorn Limestone Formation (Lower Turonian, Upper Cretaceous) of Cloud County (near Aurora), Kansas (Storrs 1999, Schumacher and Everhart 2005). The specimen, KUVP 441, is a partial skeleton consisting of partial vertebral column (51 cervical vertebrae, 18 caudal vertebrae), limb, and girdle […]

Opallionectes is a large, around 5 m long, derived cryptoclidid plesiosauroid from the Early Cretaceous of South Australia. It is known from a partial opalised skeleton, which is mounted for display in the South Australian Museum. The holotype specimen lacks a skull. It is diagnosed by the following unique combination of characters: small needle-like teeth […]

Pachycostasaurus is approximately 3.1 meters long. Its rib cage and vertebrae exhibit thickened bone (Cruickshank et al. 1996) a condition termed pachyostosis. This heavy ossification is unusual in plesiosaurs (another exception may include Kronosaurus), although it is common in basal sauropterygians, especially pachypleurosaurs. Pachycostasaurus probably used the extra ballast provided by its heavy bones to […]

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Peloneustes is one of several pliosaur genera from the Oxford Clay Formation in the UK. It is one of the better known pliosaurs from this horizon, represented by 12 nearly complete skulls and several skeletons. It is also the most abundant pliosaur from the Peterborough Member of the Oxford Clay Formation (Ketchum and Benson 2011b). […]

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Plesiosaurus was the first plesiosaur discovered and named (De la Beche and Conybeare 1821). The first 1821 description was based on partial remains so the anatomy of Plesiosaurus – particularly the identity of the isolated bones and how they articulated together – involved some guesswork. The type species (P. dolichodeirus) was named a few years […]

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Polycotylus latipinnis was the first short-necked plesiosaur to be recognised in North America (Carpenter 1996), and the first polycotylid to be described and named (Cope 1869). It was established in the same volume that coined the name Elasmosaurus and contained the infamous ‘head on the wrong end’ reconstruction (Cope 1869). However, despite their equally long […]

Rhomaleosaurus is the largest known Lower Jurassic pliosaur and was the top predator in early Jurassic marine ecosystems. It has a reinforced skull to help resist torsion and a ferocious set of teeth, a combination of characters perfect for snatching and killing cephalopods, fish, and other marine reptiles. Historically, the genus Rhomaleosaurus has been interchangeable […]

Simolestes has variously been allied with the Pliosauridae and the Rhomaleosauridae. The most noticeable difference between Simolestes and the other pliosaur taxa from the Oxford Clay (Liopleurodon, Peloneustes, Pachycostasaurus), is its much shorter snout and mandibular symphysis, a character is shares with the Rhomaleosauridae. However, this is probably a convergent character. Older descriptions of this […]

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Stratesaurus is a very small-bodied basal plesiosaur known from the lowermost Jurassic (Blue Lias Formation) of Street, Somerset . Stratesaurus is represented by three specimens. The holotype specimen (OUMNH J.10337) was named and briefly described by Benson, Evans and Druckenmiller (2012), and later described in detail along with two referred specimens by Benson, Evans and […]

The holotype specimen (KUVP 1301) of Styxosaurus is an articulated skull and anterior portion of the neck. It was found in the Niobrara Chalk near Hell Creek, Logan County, Western Kansas in 1890. It was described later that year as a new species Cimoliosaurus snowii by Williston (1890a) (and Williston 1890b), who subsequently (Williston 1906) referred […]

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The species Plesiosaurus hawkinsii was introduced in 1838 for a small plesiosaurian from Street, Somerset. The new genus name Thalassiodracon was erected decades later following an examination of a referred skull in Cambridge (CAMSM J.46986). Thalassiodracon means ‘Sea Dragon’, which “alludes to the colloquial description given to the Street marine reptile fauna by Hawkins” (Storrs […]

The holotype of Thalassomedon was discovered by R. L. Landberg in 1939 in Baca County, Colorado. Thalassomedon has a short and deep atlas-axis and 62 cervical vertebrae, and there is no pectoral or pelvic bar in the adult condition (Carpenter 1999). The species name haningtoni is sometimes wrongly spelled ‘hanningtoni’ (as in Carpenter 1999) or […]

Thaumatodracon is a relatively large rhomaleosaurid from the Lower Jurassic (Sinemurian) of Lyme Bay – the coast between Lyme Regis and Charmouth – UK. The holotype specimen (NLMH 106.058) is an almost complete skull and cervical (neck) series. It has a 60 cm long skull, and based on comparison with other rhomaleosaurids I estimate its total […]

Thililua has 30 cervical vertebrae. Each cervical has a longitudinal ridge on its lateral surfaces, this is a convergent feature with elasmosaurids. The skull of Thililua is relatively large with a short postorbital region and elongate rostrum. The type specimen (MHNGr.PA.11710) consists of a complete skull, entire cervical and pectoral series, and the first four […]

Tricleidus is a cryptoclidid from the Oxford Clay Formation of the UK. The holotype specimen (NHMUK R 3539) consists of disarticulated elements including most of skull and half the postcranium, from the Kosmoceras jasoni – Peltoceras athleta zones from the lowest deposits of the Oxford Clay Formation. The type and only species of Tricleidus is […]

Umoonasaurus is a small (~2.5 m long) leptocleidid that lived during the Early Cretaceous in Southern Australia. The holotype specimen (AM F99374), a spectacular opalised skeleton including the skull, is nicknamed ‘Eric’. It is the most complete opalised plesiosaur skeleton (and fossil vertebrate) known. It was originally described briefly as Leptocleidus sp. by Kear (2006) […]

The name Vectocleidus was erected by Benson et al. (2012b) for a leptocleidid from the Early Cretaceous of the Isle of Wight, UK. The type specimen was previously referred to Leptocleidus sp. Vectocleidus can be confidently identified as a leptocleidid but its position within the clade is unstable (Benson et al. (2012b).

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Sachs (2004) regarded ‘Woolungasaurus‘ as a junior synonym of Styxosaurus and assigned the type species (‘W. glendowerensis‘) to that genus under the new combination ‘Styxosaurus glendoweresnis‘. However, this placement was unsupported by unambiguous apomorphic characters (Kear 2007). Since ‘Woolungasaurus‘ has no unique diagnostic characters, Kear (2005) reassigned all specimens of it to Elasmosauridae indet. (indeterminate […]

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