Cymbospondylus was a basal early ichthyosaur that lived in the middle of the Triassic period. It was one of the largest ichthyosaurs, and fossils range from 6 m (18 ft) up to 10 m (30 ft) long. It was one of the least fish-like of the ichthyosaurs, lacking a dorsal fin and fluked tail. It did, however, have an elongated snout like other ichthyosaurs.
Previously, it was classified as a shastasaurid, however, more recent work finds it to be more basal (Motani, 1999).
The eel-like tail of Cymbospondylus made up almost half the total body length, and it is possible that the tail was used as a primary swimming mechanism. Like present day sea snakes, Cymbospondylus probably swam by wriggling its body from side to side. The paddle-like limbs Cymbospondylus had were serving use primarily as underwater stabilizers and slowing down the ichthyosaur's swimming speed.
Cymbospondylus fossils have been found in both Germany and Nevada, and the first species was named by Joseph Leidy in 1868.