''Eoplesiosaurus'' is an extinct

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

of basal

plesiosauroid Plesiosauroidea (; Greek: 'near, close to' and 'lizard') is an extinct clade of carnivorous marine reptiles. They have the snake-like longest neck to body ratio of any reptile. Plesiosauroids are known from the Jurassic and Cretaceous period ...

known from the

Early Jurassic The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

(most likely earliest Hettangian stage) of the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

. It contains a single species, ''E. antiquior''.

Discovery

''Eoplesiosaurus'' is known only from the

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

specimen TTNCM 8348, a complete and articulated

postcrania Postcrania (postcranium, adjective: postcranial) in zoology and vertebrate paleontology is all or part of the skeleton apart from the skull. Frequently, fossil remains, e.g. of dinosaurs or other extinct tetrapods, consist of partial or isolated sk ...

l skeleton. It preserved three-dimensionally with some gastralia presented. It was collected at

Watchet Watchet is a harbour town, civil parish and electoral ward in the county of Somerset, England, with a population in 2011 of 3,785. It is situated west of Bridgwater, north-west of Taunton, and east of Minehead. The town lies at the mouth of ...

, of

Somerset ( en, All The People of Somerset) , locator_map = , coordinates = , region = South West England , established_date = Ancient , established_by = , preceded_by = , origin = , lord_lieutenant_office =Lord Lieutenant of Somerset , lord_ ...

, from the Pre-''Planorbis'' beds of the Blue Lias Formation of the

Lower Lias Group The Lias Group or Lias is a lithostratigraphic unit (a sequence of rock strata) found in a large area of western Europe, including the British Isles, the North Sea, the Low Countries and the north of Germany. It consists of marine limestones, sha ...

. These beds likely occur below the first occurrence of the ammonite '' Psiloceras planorbis''. Thus, they probably fall within the earliest Hettangian ''P. tilmanni'' Chronozone, which is about 199.6-198 million years old, immediately following the

Triassic The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...

–

Jurassic The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...

Boundary. Plesiosaurs fossils which were discovered at Street (e.g. ''

Avalonnectes ''Avalonnectes'' is an extinct genus of small-bodied rhomaleosaurid known from the Early Jurassic period (most likely earliest Hettangian stage) of the United Kingdom. It contains a single species, ''A. arturi''. Discovery ''Avalonnectes'' is kn ...

'' and ''

Thalassiodracon ''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 t ...

''), or at penecontemporaneous strata such as the Watchet locality, represent the earliest known occurrence of the

Plesiosauria The Plesiosauria (; Greek: πλησίος, ''plesios'', meaning "near to" and ''sauros'', meaning "lizard") or plesiosaurs are an order or clade of extinct Mesozoic marine reptiles, belonging to the Sauropterygia. Plesiosaurs first appeared ...

. Hence, ''Eoplesiosaurus'' is the oldest

and one of the oldest plesiosaurs, to date.

Description

''Eoplesiosaurus'' is a proportionally long-necked plesiosaurian with at least 38 cervical vertebrae. The presence of small, conical lateral projections on the bases of the anterior cervical prezygapophyses represents its

autapomorphy In phylogenetics, an autapomorphy is a distinctive feature, known as a derived trait, that is unique to a given taxon. That is, it is found only in one taxon, but not found in any others or outgroup taxa, not even those most closely related to ...

. A

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analysis performed by Benson ''et al.'' (2012) found it to be the basalmost known plesiosauroid. The

cladogram A cladogram (from Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an evolutionary tree because it does not show how ancestors are related to ...

below shows ''Eoplesiosaurus'' phylogenetic position among other plesiosaurs following Benson ''et al.'' (2012).

Etymology

''Eoplesiosaurus'' was first described and named by

Roger B. J. Benson Roger is a given name, usually masculine, and a surname. The given name is derived from the Old French personal names ' and '. These names are of Germanic origin, derived from the elements ', ''χrōþi'' ("fame", "renown", "honour") and ', ' ( ...

, Mark Evans and Patrick S. Druckenmiller in

2012 File:2012 Events Collage V3.png, From left, clockwise: The passenger cruise ship Costa Concordia lies capsized after the Costa Concordia disaster; Damage to Casino Pier in Seaside Heights, New Jersey as a result of Hurricane Sandy; People gat ...

and the

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specime ...

is ''Eoplesiosaurus antiquior''. The generic name is derived from

Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...

''Eo'', "dawn", and ''

Plesiosaurus ''Plesiosaurus'' (Greek: ' ('), near to + ' ('), lizard) is a genus of extinct, large marine sauropterygian reptile that lived during the Early Jurassic. It is known by nearly complete skeletons from the Lias of England. It is distinguishable b ...

'' in reference to its proportionally long neck, which is also present in ''Plesiosaurus''. The specific name is derived from

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

meaning "more ancient", in reference to the old geologic age of the specimen and

Duria Antiquior ''Duria Antiquior, a more ancient Dorset'', was the first pictorial representation of a scene of prehistoric life based on evidence from fossil reconstructions, a genre now known as paleoart. The first version was a watercolour painted in 1830 b ...

(meaning "a more ancient Dorset"), an 1830 watercolour depiction of Lower Jurassic fauna, including plesiosaurs and ichthyosaurs, by

Henry De la Beche Sir Henry Thomas De la Beche KCB, FRS (10 February 179613 April 1855) was an English geologist and palaeontologist, the first director of the Geological Survey of Great Britain, who helped pioneer early geological survey methods. He was the ...

Discovery

Description

Etymology

See also