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.

[2][3] Thalassiodracon hawkinsii is known from a number of complete skeletons (lectotype: NHMUK PV OR 2018) acquired by the fossil collector Thomas Hawkins in Somerset, England during the early 1830s, before 1834.

[3][4][5] In Memoirs of Icthyosaurii and Plesiosaurii (1835) and The Book of the Great Sea Dragons (1840), Hawkins published his own illustrations after reconstructing the fossils he had obtained.

[7] It was named as Plesiosaurus Hawkinsii in 1838 by Richard Owen[2] and it was made the type species of the genus Thalassiodracon in 1996 by Storrs & Taylor.

[1] The original fossil, designated as NHMUK PV OR 2018 was bought by Hawkins in the 1830s, and is currently on display at the Natural History Museum in London, England.

[8] Three fossils found in Somerset, England originally identified as Thalassiodracon were redescribed as another small plesiosaur, Stratesaurus taylori.

[9] According to the Global Biodiversity Information Facility, there is a total of 31 fossil occurrences of Thalassiodracon hawkinsii, all located in the United Kingdom.

Thalassiodracon was a small plesiosaur in the Late Triassic (Rhaetian) to the Early Jurassic (Hettangian) of Europe (age range: 201.6 to 196.5 million years ago).

Unlike the reptiles of today, Thalassiodracon hawkinsii and other plesiosaurs were warm-blooded with a high metabolism, enabling them to have an active lifestyle.