Over the years, South Dakota has been home to a number of historic dinosaur bone discoveries, including 'Sue', the Tyrannosaurus Rex discovered on the Cheyenne River Indian Reservation, in August of 1990.

The Mount Rushmore State was back in the news when the remains of a seven-foot-long, 3,000-pound Triceratops skull 'Shady' was unearthed in the Badlands.

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And while most of the significant dinosaur bone encounters have happened in West River South Dakota, that doesn't mean we didn't have dinosaurs roaming what has now, millions of years later, become the eastern part of the state.

According to an interactive map designed by California paleontologist Ian Webster, what we now know as Eastern South Dakota and the Sioux Falls area, was once home to three main creatures, that were both land and water-based, because up until 240 million years ago, this part of the world was either completely underwater or right on the edge of a massive body of water.

One of the inhabitants was the Mosasaurus. This was described as a kind of 'ancient crocodile that could grow to over 50 feet long, with a streamlined skull bristling with teeth, a barrel-like trunk for its midsection, and a long, powerful tail'.

In 2016, a Mosasaurus fossil was discovered in the Black Hills.

Also frequenting these parts during that time frame was the Styxosaurus, which was 'approximately 36 feet long, with about half of the length being composed of a 17-foot neck. It has sharp teeth were conical and were adapted to puncture and hold rather than to cut'.

A 36-foot section of a Styxosaurus was unearthed in the Central South Dakota town of Iona, in 1945.

The third creature is the Trachodon, a plant-eating dinosaur, best known for its duckbill mouth.

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