Thunnosauria (Greek for "tuna lizard" – thunnos meaning "tuna" and sauros meaning "lizard") is an extinct clade of parvipelvian ichthyosaurs from the Early Jurassic to the early Late Cretaceous (Hettangian–Cenomanian) of Asia, Australia, Europe, North America, and South America.

Named by Ryosuke Motani in 1999, it contains the basal taxa Ichthyosaurus and Stenopterygius and the family Ophthalmosauridae.

[1][2] Thunnosauria is a node-based taxon defined in 1999 as "the last common ancestor of Ichthyosaurus communis and Stenopterygius quadriscissus and all of its descendants".

[1] The cladogram below follows the topology from a 2010 analysis by Patrick S. Druckenmiller and Erin E.

[3] Ichthyosaurus Stenopterygius "Ophthalmosaurus" natans Aegirosaurus Ophthalmosaurus Mollesaurus Athabascasaurus Brachypterygius Arthropterygius Caypullisaurus "Platypterygius" hercynicus "Platypterygius" australis Platypterygius Maiaspondylus "Platypterygius" americanus