''Thalassiodracon'' (tha-LAS-ee-o-DRAY-kon) is an

extinct Extinction is the termination of a kind of organism or of a group of kinds (taxon), usually a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and ...

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

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 ...

from the

Pliosauridae Pliosauridae is a family of plesiosaurian marine reptiles from the Latest Triassic to the early Late Cretaceous ( Rhaetian to Turonian stages) of Australia, Europe, North America and South America. The family is more inclusive than the archetypa ...

that was alive during the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch ...

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 ...

(

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest age ...

Hettangian The Hettangian is the earliest age and lowest stage of the Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (My ...

) and is known exclusively from the

Lower Lias 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, ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. The type and only species, is ''Thalassiodracon'' (''

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 Group, Lias of England. It is disting ...

'') ''hawkinsi'' (

Owen Owen may refer to: Origin: The name Owen is of Irish and Welsh origin. Its meanings range from noble, youthful, and well-born. Gender: Owen is historically the masculine form of the name. Popular feminine variations include Eowyn and Owena. ...

, 1838). Owen, R. (1838). A description of Viscount Cole's specimen of '' Plesiosaurus macrocephalus'' ( Conybeare). ''Proceedings of the Geological Society of London 2'', 663-666.

Discovery and naming

''Thalassiodracon hawkinsi'' is known from a number of complete skeletons (

lectotype In biology, a type is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally attached. In other words, a type is an example that serves to anchor or centralizes the ...

: BMNH 2018) acquired by the fossil collector Thomas Hawkins in

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_ ...

during the early 1830s, before 1834. Hawkins, an eccentric

Pre-Adamite The pre-Adamite hypothesis or pre-Adamism is the theological belief that humans (or intelligent yet non-human creatures) existed before the biblical character Adam. Pre-Adamism is therefore distinct from the conventional Abrahamic belief that Ada ...

who had his fossils heavily restaured and illustrated by distinguished artists in expensive editions to propagate his ideas, named these ''Plesiosaurus triotarsostinus'' in 1834 and ''Hezatarostinus'' in 1840 but these names are generally disregarded. ''Thalassiodracon'' lived in the Late

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

(

) to the Early

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), 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 J ...

(

) of Europe (age range: 201.6 to 196.5 million years ago).Paleobiology Database
/ref> It was named as ''Plesiosaurus Hawkinsii'' in 1838 by

Richard Owen Sir Richard Owen (20 July 1804 – 18 December 1892) was an English biologist, comparative anatomist and paleontologist. Owen is generally considered to have been an outstanding naturalist with a remarkable gift for interpreting fossils. Owe ...

and it was made the type species of the genus ''Thalassiodracon'' in 1996 by Storrs & Taylor. A replica of 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 several ...

specimen, replica catalogued as LDUCZ-X227, has been in the collection of the

Grant Museum of Zoology and Comparative Anatomy The Grant Museum of Zoology and Comparative Anatomy is a natural history museum that is part of University College London in London, England. It was established by Robert Edmond Grant in 1828 as a teaching collection of zoological specimens and ...

London London is the capital and largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary down to the North Sea, and has been a majo ...

since 1890 after being catalogued by

Ray Lankester Sir Edwin Ray Lankester (15 May 1847 – 13 August 1929) was a British zoologist.New International Encyclopaedia. An invertebrate zoologist and evolutionary biologist, he held chairs at University College London and Oxford University. He was th ...

, and it is a cast of a specimen created in 1862 by

Henry Augustus Ward Henry Augustus Ward (March 9, 1834 – July 4, 1906) was an American naturalist and geologist. Biography Henry Augustus Ward was born in Rochester, New York on March 9, 1834. After attending Williams College and the Lawrence Scientific School ...

. The original fossil, catalogued as BMNH 2018 and also bought by Hawkins in the 1830s, can be seen on display at the

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

, also in London, England. The genus name ''Thalassiodracon'' means "sea dragon", while the specific name ''hawkinsi'' honours Hawkins.

Description

left, Life restoration of ''Thalassiodracon hawkinsi''. ''Thalassiodracon'' was a small plesiosaur, measuring approximately long and weighing . It has a skull length of , neck length of , and trunk length of . The neck of ''Thalassiodracon'', however, was slightly shorter than that of subsequent Plesiosaurs. Ward, Henry A. (1866). ''Catalogue of Casts and Fossils From the Principle Museums of Europe and America with Short Descriptions and Illustrations.'' Benton and Andrews. Rochester, N.Y. The cervical vertebrae were between 27 and 31, while those of ''Plesiosaurus'' were 35 - 37. Moreover, the skull was unusually short and equipped with long teeth. The orbits were very large, with sclerotic rings. Like all plesiosaurs, this animal had legs like paddles for swimming in the sea. A computed tomography of an exceptionally preserved skull, and examination of other specimens (Benson ''et al.'', 2011) yields new anatomical data. ''Thalassiodracon'' had a dorsomedian ridge on the premaxilla, a squamosal bulb, four premaxillary teeth, and a heterodont maxillary dentition.Storrs, G. W & Taylor, M. A. (1996). Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England. Jour. Vert. Paleo. 16:403-20.

Classification

''Thalassiodracon'' was originally placed in the genus ''

''. It has been classified in a new genus ''Thalassiodracon'' many years later following an examination of a skull. This animal is considered one of the oldest representatives of the group of plesiosaurs, perhaps ancestral to the superfamily of

Pliosauroidea 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 tooth ...

(short-necked plesiosaurs).Plesiosauria
/ref> The following

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 d ...

follows an analysis by Ketchum & Benson, 2011.

References

{{Portal bar, Paleontology, United Kingdom Plesiosaurs of Europe Triassic plesiosaurs Early Jurassic plesiosaurs of Europe Pliosaurids Fossil taxa described in 1996 Sauropterygian genera

Discovery and naming

Description

Classification

See also

References