During much of the Cretaceous South Dakota was submerged by an epicontinental sea, known as the Western Interior Seaway. This seaway provided a warm and tropical habitat for a large number of animals, including cephalopods (ammonites, squids & nautilus), marine reptiles (mosasaurs & plesiosaurs), giant turtles (Archelon), early birds (Hesperornis), and flying reptiles (Pteranodon). South Dakota is known for an abundance of ammonite fossils. Ammonites, like all living cephalopods, were predatory, but few reached a size that would place them at the top of the food chain. These beautiful animals had to be ever watchful of the even larger predators looking to make a meal of them.

Incredible preservation of an obvious mosasaur bite!