What are two prehistoric animals found in Arkansas?

Answer 1

Up until the start of the Permian, Arkansas was mostly submerged and the only species I could find were marine invertebrates, such as brachiopods.

By the early Jurassic, Arkansas once again began to be submerged, and it was mostly underwater throughout the Cretaceous period. Fossils known from this time include marine invertebrates, sharks, fish, and a sea turtle called Bothremys. Plesiosaurs and mosasaurs probably also lived there, although their fossils haven't been found in Arkansas yet.

The southwestern portion of Arkansas was a coastal region of land during the Cretaceous period. Fossil footprints from sauropods (huge, four legged, plant eating dinosaurs with bulky bodies and long necks) have been found here. Fossilized foot bones of a species of theropod known as Arkansaurus fridayi were found here, as well. Because it is only known from foot bones, we can only guess about most of Arkansaurus, but it appears that it was similar to Ornithomimus, being a fast moving omnivore, and was somewhere between 6 and 15 feet tall.

The sea finally retreated from Arkansas for good by the mid to late Tertiary period. The southern portion of the state was now covered by rivers and swamps. During the Ice Age, the climate cooled, and Arkansas was now home to grasslands and forests. Animals that lived there included mammoths, mastodon, giant ground sloths, saber-toothed cats, American lions, and several species of bison, to name a few.

See the related link for more information on Paleontology in Arkansas.