1825, from Modern Latin Pleisiosaurus (1821), coined by English paleontologist William Daniel Conybeare (1787-1857) from Greek plesios "near," related to pelas, + -saurus.
Examples from the Web for plesiosaurus
The one marked C belongs to Plesiosaurus dolichodeirus, the species represented in our plate.Extinct Monsters|H. N. Hutchinson
These diagrams of the plesiosaurus, the ichthyosaurus, the pterodactyle, give you a notion of some of these extinct reptiles.The Past Condition of Organic Nature|Thomas H. Huxley
That monster could have been no other than the Plesiosaurus, one of the most wonderful animals that has ever existed.A Strange Manuscript Found in a Copper Cylinder|James De Mille
Another fish-lizard, well and unfavorably known by his neighbors of the sea, was the Plesiosaurus.The Adventures of a Grain of Dust|Hallam Hawksworth
Neither he nor Mr. Newman insist that the "great unknown" must be the Plesiosaurus itself.