It was originally classified as a species of Plesiosaurus, later as the second named species of Thaumatosaurus (defunct name, meaning "wonder reptile") and ultimately as a species of Eurycleidus or Rhomaleosaurus.
The large pliosaurs, like the Jurassic Rhomaleosaurus, Liopleurodon and Pliosaurus, and the Cretaceous Kronosaurus and Brachauchenius, were the superpredators of the Mesozoic seas, around 7 to 12 meters in length, and filled a similar ecological role to that of killer whales today.