Ichthyosauria n. pl. : An extinct order of marine reptiles, including Ichthyosaurus and allied forms; -- called also Ichthyopterygia. They have not been found later than the Cretaceous period.

Example:


Taxonomy
ichthyosaurs, fish, Ichthyosaur skeleton, Ryosuke Motani, species, specimens, Family Ichthyosauridae, dolphin, Ichthyopterygia, reptiles, tail, skeleton, genus, teleost fish, Order ICHTHYOSAURIA, lizard, free encyclopedia, fossil.

Defination from the web:
... They belong to the order known as Ichthyosauria or Ichthyopterygia ('fish flippers' - a designation introduced by Sir Richard Owen in 1840, ...