Plesiosaurs (プリシオサウル Purishiosauru) where common sight in Tsuburaya's series, Dinosaur Task Force, Koseidon.
The Plesiosaurs, along with many other dinosaur and ancient reptiles, lived peacefully several million years ago, that is, until a race of aliens found that the fossil fuels of Earth where strongest when the dinosaurs lived. As such, constant attacks took place in Ancient Japan, with Aliens sending dinosaurs fleeing for their lives and some even to their deaths. The Plesiosaurs usually stayed away from conflict and remained in the ocean, but where under attack when the Aliens sucked water from the sea, flinging the marine reptiles skyward.
In the series finale, the Plesiosaurs, like most of the other dinosaurs and ancient life, where killed by a giant meteor, with Koseidon cursing the fact he could not save the ancient animals.
- The Plesiosaurus props where two of the first original props made for the show. All others came from Dinosaur War Aizenborg and Dinosaur Catcher.
- While they look similar, the Plesiosaurs are not reused props from Legend of Dinosaurs and Monster Birds, a Toei film.