5. Elasmosaurus - Next up on our trip across time is Elasmosaurus. One of the largest of the Plesiosaurs ever discovered, Elasmosaurus grew up to 46 feet long, which was about half neck. Equipped with a fairly small head, Elasmosaurus would have been incapable of going after large prey, so it would have mostly stuck with fish. Elasmosaurus lived during the Late Cretaceous, a time when much of North America was "Beneath the Waves," under something that we call the "Western Interior Seaway." Remains of this animal were first uncovered in Kansas, but it almost certainly swam all over the seaway, including in Colorado.
6. Dunkleosteus - Dunkleosteus, a creature we talked about a few weeks ago in our post about the Coelacanth, is another fascinating animal. Almost thirty-five feet in length, Dunkleosteus was a member of the Placoderms, a group of armored fish that were only around for about 50 MYA. A long time, to be sure, but not very long compared to the 400 million year reign of the sharks. While the Placoderms themselves lived during the Silurian and Devonian Periods, they went extinct during the transition to the Carboniferous Period, at the end of the Devonian. Dunkleosteus fossils have been discovered in North America, Poland, Belgium, and Morocco.
This post is part of the "Top Ten: Extinct Sea Monsters" series. For the rest of the posts in this series, click HERE.