Cymbospondylus was an early member of the Icthyosaur group, which looked slightly like modern dolphins. Cymbospondylus had no dorsal fin and its tail was long like an eel's.

Its long tail made it a powerful swimmer, it patrolled in deep offshore waters looking for prey.

Cymbospondylus had a skull 1m long with short, sharp teeth good for grabbing quite large reptiles but it favoured fish and cephalopods such as ammonites.

Cymbospondylus appears to have given birth to live young as it had no way to lay eggs.