An ancient sea once divided North America from north to south; 70-million-year-old creatures from its waters still shimmer like gemstones

Millions of years ago, South Dakota was covered by a vast inland sea. This ancient seaway supported diverse marine life, including ammonites and marine reptiles. Today, fossils from this period are displayed at the Smithsonian’s National Museum of Natural History. These ancient shells still shine due to their mother-of-pearl composition. Discoveries continue to reveal insights into prehistoric marine ecosystems and Earth’s history.