Mixosaurus is an extinct genus of Middle Triassic (Anisian to Ladinian, about 250-240 Mya) ichthyosaur.

[3] Mixosaurus was a small ichthyosaur, measuring 73–100 cm (2.40–3.28 ft) long and weighing 2.2–5.7 kg (4.9–12.6 lb).

Examples of the dental variation are the extent of the dental groove in the upper jaw, the shape and size of the teeth and the number of rows of teeth [4] Previous authors assigned other species to the genus, including M. atavus (Quenstedt, 1852), M. callawayi Schmitz et al., 2004, M. panxianensis Jiang et al., 2006 and M. yangjuanensis Liu & Yin, 2008.

[12][13][14] Many specimens of Mixosaurus cornalianus have been found from the Middle Triassic of Monte San Giorgio and the Tessin areas on the border of Italy and Switzerland.

The specimens have been found in the Guanling Formation, which consists of thinly bedded bituminous limestones and marls.

The specimens found have important Mixosaurid characteristics such as a long sagittal crest along the top of the skull but is seen as a different species because there is no external contact between the jugal and the quadratojugal.

This is evidence for its transitional position between basal early Triassic ichthyosaurs and more derived Jurassic and Cretaceous species; who have disc shaped circular centra of the vertebrae.

Mixosaurus contains M. cornalianus, M. kuhnschnyderi and M. xindianensis, Barracudasauroides contains B. panxianensis, Phalarodon contains P. fraasi and P. callawayi, and Contectopalatus contains C.

It was suggested that Tholodus schmidi should be included in Mixosauridae but only dental material has been found so it is difficult to assign it to a genus.