An ancient ocean once divided North America from north to south; aquatic creatures from 70 million years ago still sparkle like gems
South Dakota is one of the most landlocked states in the United States. It is over 1,000 miles from both the Pacific and Atlantic Oceans. It’s hard to imagine that this dry land was once covered with water.But 70 million years ago, the area looked completely different. Much of what is now South Dakota lies beneath a vast inland sea called the Western Interior Seaway. The ocean cuts through the middle of North America, splitting the continent in two. Its waters were home to giant marine reptiles, sharks, and ammonites that are related to today’s squids and octopuses.Although the ocean disappeared millions of years ago, it left behind extraordinary clues. Some of the best-preserved fossils from these waters are currently on display at the Smithsonian’s National Museum of Natural History in Washington, D.C., Smithsonian Museum Magazine reports.The exhibit, “From These Lands,” features hundreds of fossils and artifacts from across the United States, including colorful ammonite shells that still sparkle today.
vast inland sea
The ammonite fossils on display in the museum date from approximately 69 to 72 million years ago. They lived during the final years of the dinosaurs, when pterosaurs still flew the skies and giant marine reptiles ruled the oceans.The Western Interior Seaway has existed for more than 30 million years. About 100 million years ago, during the Cretaceous Period, sea levels rose and ocean water spread across central North America. This created a vast inland sea that stretched from the Arctic Ocean to what is now the Gulf Coast.
North Carolina’s state fossil is the tooth of the megalodon, Otodus megalodon, commonly known as the “megalodon.” (Smithsonian National Museum of Natural History)
Although much shallower than today’s oceans, the seaways were teeming with life. Scientists have discovered fossils of giant marine reptiles in Kansas and giant reef-building clams in Utah. As the Earth’s climate cooled toward the end of the Cretaceous, polar ice formed and sea levels dropped. Slowly, the sea disappeared and the two halves of the continent were reunited.The ancient oceans left behind some things that still benefit humans today. Over millions of years, the rocks in the seaways broke down and formed fertile soil. This soil would later make the American Midwest one of the most important agricultural regions in the United States.
Why do seashells still sparkle?
One of the most striking things about the South Dakota fossils is that they still sparkle with colorful patterns. Ammonite shells are partly made of nacre, also known as mother-of-pearl. It is this material that gives pearls their luster.During fossilization, the mother-of-pearl layers become more visible than they were when the animal was alive. That’s why these shells still reflect light millions of years later.Ammonites come in different sizes. Some grow to about six feet wide, but they feed primarily on tiny sea creatures such as plankton.
This starfish fossil is Hudsonaster narrawayi, which lived 457-449 million years ago (Smithsonian National Museum of Natural History)
Fossils from across the United States
The exhibit also shows that marine fossils are not just found in coastal areas. One of the fossils on display is a starfish from Minnesota that lived about 457 to 449 million years ago, when warm, shallow seas covered much of the region.Scientists say this is possible because the Earth’s surface has changed many times over millions of years. Continents move, sea levels rise and fall, and new rocks form. As a result, fossils from ancient oceans can now be found far from today’s coastlines.Researchers have also found traces of some of the earliest animal life in Utah, ancient coral reefs in Ohio and fossilized shark teeth dating back about 20 million years in South Carolina. Evidence of ancient oceans can also be found in places like Ohio. The rocks beneath Ohio were formed hundreds of millions of years ago, when plants first began to grow on land. Fossils of brachiopods (a type of clam that lived on Earth for more than 500 million years) and crinoids (relatives of today’s starfish) can still be found there.Ohio is also famous for the fossil of an ancient shark called the Cladoselache. Many fossils were discovered during the construction of Interstate 71 in the 1960s, and scientists are still studying them today.
