ich·thy·o·saur 
(ĭkthē-ə-sôr′)
(ĭkthē-ə-sôr′)n.
Any of various extinct marine reptiles of the group Ichthyosauria or Ichthyopterygia of the Mesozoic Era, having a long flexible body with fins and an elongated toothed snout.
[From New Latin Ichthyosaurus, type genus of the group : Greek ikhthuo-, ichthyo- + Greek sauros, lizard.]