Ichthyosaur n. : One of the Ichthyosaura.

Example:
Why are the tails of a dolphin, Ichthyosaur and swordfish considered to be?

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:
ichthyosaurs, the giant marine reptiles that resembled fish and dolphins that lived during the Mesozoic Era.