Fossils of both marine animals and land plants that lived during the Mississippian and Pennsylvanian periods are found in both the Arkansas River Valley and the northern highlands. The West Gulf Coastal Plain covers most of southern Arkansas. In Arkansas, it can be divided into two parts. Farthest from the sea is an area where the sediments date back more than sixty-five million years to the Cretaceous Period, when dinosaurs still stalked the land. Arkansas best fossil sites are here.
People find the remains of mosasaurs, sharks, turtles, crocodiles, and fishes.
Between this area and the sea is an area of younger Cenozoic Era sediments. Cenozoic fossils include shark and ray teeth, bryozoans, and bivalves. The most recent epoch of the Cenozoic was the Pleistocene, or Ice Age, which ended less than 20,000 years ago. Fossils of Pleistocene animals are scattered across Arkansas. One good place to look for such fossils is along the Mississippi River Plain in eastern Arkansas.