It was named in 1904 by paleontologist John Campbell Merriam to include the genus Thalattosaurus from California.

Thalattosauroids make up the "traditional" thalattosaurs with large downturned snouts, short necks, and long, paddle-like tails.

Thalattosauria includes North American genera such as Thalattosaurus and Nectosaurus as well as recently described Chinese forms such as Xinpusaurus.

More recent phylogenetic studies have come upon the same conclusions, but refer to the group as Thalattosauroidea in order to contrast it with another superfamily of thalattosaurs, Askeptosauroidea.

[1][2] Below is a cladogram from Wu et al. (2009) showing the phylogenetic relationships of Thalattosauroidea:[3] Askeptosauroidea Nectosaurus Xinpusaurus Kössen-Form Agkistrognathus Paralonectes Thalattosaurus Clarazia Hescheleria