Thalassiodracon

Thalassiodracon (tha-LAS-ee-o-DRAY-kon) is an extinct genus of small pliosaurs. The type and only species, is Thalassiodracon hawkinsi Owen 1840.[1]

Thalassiodracon
Temporal range: Rhaetian - Hettangian
Thalassiodracon hawkinsi found in the Lower Lias strata, Street, Somerset, England.
Scientific classification
Kingdom:
Animalia
Phylum:
Chordata
Class:
Sauropsida
Superorder:
†Sauropterygia
Order:
†Plesiosauria
Suborder:
†Pliosauroidea
Family:
†Pliosauridae
Genus:
†Thalassiodracon

Storrs & Taylor 1996
Binomial name
†Thalassiodracon hawkinsi
(Owen, 1838)

Discovery

These animals are known from a number of complete skeletons (Holotype: BMNH 2018) found by the fossil collector Thomas Hawkins in Somerset, England.[1] They lived in the Late Triassic (Rhaetian) to the Early Jurassic (Hettangian) of Europe (age range: 201.6 to 196.5 million years ago).[1]

The genus name Thalassiodracon means "sea dragon", while the species name hawkinsi honours its discoverer.

Description
Life restoration of Thalassiodracon hawkinsi.

This marine reptile measured 1.5–2 m. (5-6.5 ft) had a relatively long neck but the small skull was proportionally larger than Plesiosaurus, being 1/10 of the total body length.

The neck of Thalassiodracon, however, was slightly shorter than that of subsequent Plesiosaurs.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.[2][3]

Classification
Thalassiodracon hawkinsi skeleton, Natural History Museum in London
Fragmentary specimen

Thalassiodracon was originally placed in the genus Plesiosaurus. 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 (short-necked plesiosaurs).[4]

The following cladogram follows an analysis by Ketchum & Benson, 2011.[5]

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See also

References
  1. Paleobiology Database
  2. 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.
  3. Roger B. J. Benson, Karl T. Bates, Mark R. Johnson & Philip J. Withers Cranial anatomy of Thalassiodracon hawkinsii (Reptilia, Plesiosauria) from the Early Jurassic of Somerset, United Kingdom - Journal of Vertebrate Paleontology - Volume 31, Issue 3, 2011
  4. Plesiosauria
  5. Hilary F. Ketchum and Roger B. J. Benson (2011). "A new pliosaurid (Sauropterygia, Plesiosauria) from the Oxford Clay Formation (Middle Jurassic, Callovian) of England: evidence for a gracile, longirostrine grade of Early-Middle Jurassic pliosaurids". Special Papers in Palaeontology. 86: 109–129. doi:10.1111/j.1475-4983.2011.01083.x (inactive 2020-03-17).CS1 maint: uses authors parameter (link)
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