Source : Webster's Revised Unabridged Dictionary (1913)

Ichthyosaur \Ich"thy*o*saur\, n. [Cf. F. ichthyosaure.]
   (Paleon.)
   One of the Ichthyosaura.

Source : WordNet®

ichthyosaur
     n : any of several marine reptiles of the Mesozoic having a body
         like a porpoise with dorsal and tail fins and
         paddle-shaped limbs
     [also: {ichthyosauruses} (pl)]