The species Plesiosaurus hawkinsii was introduced in 1838 for a small plesiosaurian from Street, Somerset. The new genus name Thalassiodracon was erected decades later following an examination of a referred skull in Cambridge (CAMSM J.46986). Thalassiodracon means ‘Sea Dragon’, which “alludes to the colloquial description given to the Street marine reptile fauna by Hawkins” (Storrs and Taylor, 1996, p.404). Three specimens were figured by Hawkins in his “Book of the great Sea Dragons” (1840). Thalassiodracon is frequently regarded as the most basal pliosauroid. T. hawkinsii is the type and only species. The type specimen is NHMUK 2018*, a complete skeleton.
The cranial anatomy of Thalassiodracon was described in detail by Storrs and Taylor (1996) and Benson et al. (2010).
Thalassiodracon lectotype specimen (NHMUK 2018*). 
Thalassiodracon lectotype specimen (NHMUK 2018*), on display in the Natural History Museum , London. 
Cast of the Thalassiodracon lectotype specimen (NHMUK 2018*), on display in the Bristol Museum and Art Gallery. 
Thalassiodracon paralectotype (NHMUK 2020* [14551]) 
Thalassiodracon paralectotype (NHMUK 2020* [14551]) 
Thalassiodracon paralectotype (NHMUK 2020* [14551]) on display in the Natural History Museum London. 
Thalassiodracon paralectotype (NHMUK 2022*[12549]). 
Thalassiodracon hawkinsi model at Crystal Palace Park, by Benjamin Waterhouse Hawkins.
