Megalonyx jeffersoni, ground sloth skeleton Triceratops then Secretary of the Smithsonian

then Secretary of the Smithsonian Institution

Atlasaurus is represented by a single

North America was divided by a great inland sea (known as the Western Interior Seaway) which stretched from the Gulf of Mexico to the Arctic Circle

Some are most like cnidarians

Unlike most other placoderm orders

Megalonyx jeffersoni, ground sloth skeleton Triceratops then Secretary of the SmithsonianPresident, Thomas Jefferson, scientifically described fossil bones given to him by saltpeter miners found in a Monroe County cave in 1797. Jefferson thought they were the claws of a giant cat. In 1799 Casper Wistar re described the bones as a new species of extinct giant ground sloth and named it in honor of President Jefferson. Only recently have the bones been Carbon 14 dated at over 38,000 year old. On March 8, 2008 Megalonyx jeffersoni became the