ichthyosauria(n = noun.animal) order ichthyosauria - extinct marine reptiles: ichthyosaurs;
is a kind of animal order
is a member of archosauria, subclass archosauria

   An extinct order of marine reptiles, including Ichthyosaurus and allied forms; -- called also Ichthyopterygia. They have not been found later than the Cretaceous period. [1913 Webster]

order ichthyosauria