Eons Season 2018 Episode 43 When Sharks Swam the Great Plains ( Air Date 2018-12-04 ) Genre Documentary category. Overview "If you’ve ever been to, or lived in, or even flown over the central swath of North America, then you’ve seen the remnants of what was a uniquely fascinating environment. Scientists call it the Western Interior Seaway, and at its greatest extent, it ran from the Caribbean Sea to the Canadian Arctic.".