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.