1) Animal order 2) Order 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.
Ich`thy·o·sau'ri·a noun plural [ New Latin See Ichthyosaurus .] (Paleon.) An extinct order of marine reptiles, including Ichthyosaurus and allied forms; -- called also Ichthyopterygia . They have not been found later than the Cretaceous period. 
[n] - extinct marine reptiles: ichthyosaurs
Ichthyosauria An order of highly specialized marine reptiles in the subclass Diapsida, characterized by an elongated snout and a fish-shaped body, and generally very fishlike; some authorities group them in a separate subclass, Ichthyopterygia, because of their great divergence from the basic reptilian pattern; Middle Triassic to Cretaceous.
order Ichthyosauria noun extinct marine reptiles: ichthyosaurs