looking up at a dinosaur hanging from ceilingPhoto Credit: Meg Kumin

An ancient sea and the life that thrived in it shaped the contour of the land we know

Kansas is known for a few things—wheat, beef, sunflowers, sports—not so much water, though, and certainly not the sea. That hasn’t always been the case. Kansas has been covered by seas several times, during the Pennsylvanian and Permian periods 320 to 245 million years ago, and most recently, the Cretaceous Period.

Paleontologist and former University of Kansas Natural History Museum director Leonard “Kris” Krishtalka explains that this sea, the Western Interior Sea, covered much of Kansas about 100 million to 80 million years ago, and that it receded and returned several times, draining for the last time with the geologic lifting of the Rocky Mountains. But the evidence the seas left behind is rock solid.

“What the seaway accomplished was depositing layers and layers and layers of limestone and chalk, made up of the compressed shells of trillions and trillions of single-celled organisms called foraminifera,” he says. “When they died, they sank to the bottom of the seaway, and their shells, made of calcium, were compacted. In parts of Western Kansas, the chalk rises as high as 500 feet.”


ksm-monument-rocksPhoto Credit: Kansas Tourism


In the 1800s, scientists would learn the limestone held even more secrets left by the ancient sea because the chalk and limestone preserved the skeletons of the animals that lived there.

“The seaway was teeming with invertebrates such as starfish, squids, crinoids—relatives of squid and octopi—but also it was populated by fish and reptiles that would make you not want to go swimming in that sea,” he says. “We’re talking about 35 to 40-foot mosasaurs, crocodile-like swimming reptiles with huge jaws.”

A 45-foot mosasaur skeleton hangs in the entryway of the KU Natural History Museum, home to several impressive Kansas chalk bed fossils, including a plesiosaur (think Loch Ness Monster with deadly sharp teeth) and a giant fish called Xiphactinus.

Krishtalka adds that pterosaurs, giant flying reptiles, would soar over the Kansas sea and feed exclusively on the marine life. Several pterosaur fossils also ended up preserved in the Kansas chalk.

Fossils from Kansas chalk are so pristine, they have been collected in all the major world museums, from the Smithsonian in Washington D.C. to the British Museum in London.

“Many of those specimens were collected by Charles Sternberg and his three sons,” Krishtalka says.

Sternberg’s fossils and legacy live on at the Sternberg Museum of Natural History in Hays, where several exhibits inform visitors about Kansas’ ancient seas.

“We have a cool exhibit that shows the types of rocks left in Kansas while there was a seaway, which includes sandstone, mudstone—or shale—and limestone,” says museum director Dr. Reese Barrick. “Each of these types of rocks represent how deep the water was.”

Barrick explains sandstone is formed in shallow water from ancient beaches, mudstone (shale) a bit deeper, and limestone in the deepest water, which, in Kansas, was generally a few hundred feet at most. The fossils found in the different types of rocks indicate the depth at which those animals lived.


ksm-sternberg-fish-in-fishPhoto credit: Andrea Etzel/Kansas Tourism

“The fossils that we have range from invertebrates like plants, to giant clams called inoceramids,” Reese says. “The clam fossils are found in limestone and thus lived in the deeper water, as did ammonites, big, coiled animals that look like the modern nautilus. We also have vertebrates, including all sizes of fish, from very small to incredibly large, and sharks that ate clams and fish, and other large vertebrates, including plesiosaurs.

“The craziest thing you see in the Cretaceous that you wouldn’t expect are birds,” Reese adds, explaining that, at one time, the feathered dinosaur Hesperornis sat on the surface of the Kansas sea and dived under the water to feed. Their habits, in fact, were much like modern loons, but they were far larger and had other key differences. “They evolved from birds that were flying, they adapted to the oceans, and they had teeth.”

The Sternberg is also home to one of the most famous fossils in the world.

“The fish within a fish—or the Gillicus within a Xiphactinus,” Reese notes. The fossil is unusual, Reese explains because the 14-foot Xiphactinus would’ve had to have eaten the Gillicus and died soon after, as the Gillicus skeleton is complete and undigested.

But it wasn’t just rocks and fossils the ancient seas left behind in Kansas. Aaron Strain, underground manager at the Strataca salt mine in Hutchinson, explains the seas that rose and fell over Kansas also deposited a whole lot of salt.

“About 275 million years ago, the climate warmed dramatically, and the salty seas began to dry up as a result,” Strain says. “As the climate continued to warm, the water began to evaporate, depositing gypsum, salt, and other evaporites.”

Strain explains that 80 feet of water is needed to form one foot of salt, meaning the cycle of deposition and evaporation could have continued for thousands or millions of years to form the Hutchinson Salt Member, which is 400 feet thick in some areas.

“What we know for sure is the Hutchinson salt underlies most of south-central Kansas, about 200 miles north-south and 150 miles east-west. Some estimates say there are 30,000 billion tons of salt in the deposit. Due to the inclusion of other minerals, some of the salt can be a red, orange, or pinkish color, as opposed to the transparent white associated with halite,” he says.


ksm-stratacaPhoto credit: Kansas Tourism

The mine in Hutchinson is one of three Kansas salt mines and has been operational for over 100 years. “The salt that comes out is about 95% pure sodium chloride, and is mainly used to deice roads, but also for industry and agriculture uses,” Strain says.

Visitors to Strataca can take the long ride down the elevator shaft into the cool mine, the walls of which sparkle with the ancient sea salt.

Krishtalka notes the evidence of Kansas’ ancient seas is not only in the museums and mines but almost everywhere, as sea fossils are easy to find and pick up off the ground or in roadcuts.

Though the Western Interior Sea has not been with us for millions of years, its legacy surrounds us.