Named By: G. W. Storrs & P. S. Taylor - 1996.
Synonyms: Plesiosaurus eleutheraxion, Plesiosaurus eleutheraxon, Plesiosaurus etheridgii, Plesiosaurus hexatarsostinus, Plesiosaurus pentatarsostinus, Plesiosaurus triatarsostinus, Plesiosaurus triotarsostinus.
Classification: Chordata, Reptilia, Sauropterygia, Plesiosauria, Pliosauroidea?
Species: T. hawkinsi (type).
Size: Around 1.5 to 2 meters long.
Known locations: England - Lias Group - Blue Lias Formation, White Lias Formation.
Time period: Rhaetian of the Triassic to the Hettangian, possibly as late as the early Pliensbachian of the Jurassic.
Fossil representation: Several almost complete individuals.
fossils were first identified and described as belonging to a species
by Richard Owen in 1840. It was not until over one
and a half centuries later that the actual description of the fossils
belonging to a distinct genus would come to pass. In addition to this
several more species of Plesiosaurus are now
identified as represented
by actual specimens of Thalassiodracon. Many of
Plesiosaurus species were named all the way back in
century when Plesiosaurus was still very new to
science and was already
suffering the effects of being a ‘wastebasket taxon’ where anything
remotely similar to the type fossils were immediately lumped into the
genus as a new species.
Thalassiodracon is an interesting genus, one that some have identified as a plesiosaur despite most others considering the genus to actually represent a pliosaur. The main difference between the two groups is that plesiosaurs developed longer necks and smaller heads for more efficient hunting of fish, while pliosaurs had shorter necks and proportionately larger heads for hunting larger marine creatures, including plesiosaurs. Thalassiodracon is quite primitive in its development which means that the dividing line between plesiosaur and pliosaur is more blurry in this genus. However, the skull of Thalassiodracon is noted for being quite large in relation to the body, a feature that has been identified as tipping Thalassiodracon over to the pliosaurs.
Although possibly a primitive pliosaur, the small size of Thalassiodracon meant that it was still probably a hunter of fish and maybe smaller marine reptiles, including small juveniles of larger genera. Later pliosaurs such as Pliosaurus and Brachauchenius would grow to much larger sizes and fulfil niches amongst the apex predators of the Mesozoic oceans.
Thalassiodracon quite simply means ‘sea dragon’, while the type species name T. hawkinsi is in honour of Thomas Hawkins, the person who discovered the first Thalassiodracon fossils.
- Report on British fossil reptiles - Richard Owen - 1840.
- A juvenile plesiosaur (Plesiosauria: Reptilia) from the Lower Lias (Hettangian: Lower Jurassic) of Lyme Regis, England: a pliosauroid-plesiosauroid intermediate? - A. R. I Cruickshank - 1994.
- Cranial anatomy of a new plesiosaur genus from the lowermost Lias (Rhaetian/Hettangian) of Street, Somerset, England - G. W. Storrs and M. A. Taylor - 1996.
- Cranial anatomy of Thalassiodracon hawkinsii (Reptilia, Plesiosauria) from the Early Jurassic of Somerset, United Kingdom - R. B. J. Benson, K. T. Bates, M. R. Johnson & P. J. Withers - 2011.
- Faunal turnover of marine tetrapods during the Jurassic–Cretaceous transition - R. B. J. Benson and P. S. Druckenmiller - 2013.