In Frank Baum’s “The Wonderful Wizard of Oz,” a rogue twister transports a young Dorothy from her Kansas farm to the Land of Oz. Once there, she’s given a pair of magical slippers to help her on her adventure. Had the twister brought her back in time to Kansas during the Late Cretaceous period, she would have gotten better use out of a lifeboat.
For well over a century, Kansas has been “America’s Breadbasket,” boasting over 45 million acres of farmland and leading the nation in wheat and sorghum production. But the state’s land is also productive in another, perhaps more surprising, way: marine fossils.
Between 100 million and 66 million years ago, Kansas, as well as the bulk of western and middle North America, was underwater.
During the Late Cretaceous period, North America was split into two halves by the Western Interior Seaway, a 3,000-mile-long inland ocean. Land all the way from Canada to the Gulf of Mexico was underwater.
This ocean was a result of both the climatic and geologic conditions at the time.
During the Late Cretaceous, the Earth entered the Cretaceous Thermal Maximum, a period of about 12 million years during which global temperatures skyrocketed.
“The climate overall was much warmer,” Dr. Amelia Zietlow, a recent graduate of the Richard Gilder Graduate School at the American Museum of Natural History, said. “There were no ice caps during the Late Cretaceous at all, so sea levels were higher.”
During this period, two tectonic plates, called the Farallon and Kula plates, collided with the main North American plate and subducted beneath it, forming a large basin. The higher sea levels filled the basin with seawater, forming the Western Interior Seaway.
The seaway was a warm environment, and, due to being inland, relatively shallow as well. On the surface, the seaway would have appeared similar to many modern oceans, but there were several key differences.
“There weren’t modern coral reefs,” Zietlow said. “A lot of the seaway, especially in the deeper parts, the floor was covered in these giant clams called inoceramids, and they got to be several meters across.”
The absence of coral reefs, as well as the types of marine plantlife present, would have made the seaway an alien place compared to today’s oceans. Occupying this alien ocean were equally alien creatures.
Instead of soaring gulls and breaching whales, the Western Interior Seaway was home to truck-sized pterosaurs and carnivorous aquatic reptiles. Some species would have been more familiar, like sea turtles, sharks and fish. One of these Cretaceous fish, however, was unlike anything alive today.
“Probably the most famous one is Xiphactinus,” Zietlow said. “It kind of looks like a tarpon, except it has a bunch of crazy teeth up front. They got to be huge, like up to 20-feet long.”
Xiphactinus has been nicknamed “the bulldog fish” by scientists due to its short, broad head and array of giant, sharp teeth. This animal would have been the glutton of the seaway, evidenced by a fossil specimen preserved with a 6-foot-long fish inside its stomach cavity. This Xiphactinus and its last meal are now immortalized at the Sternberg Museum of Natural History in Hays, Kansas.
Predators of the seaway didn’t just live in the water.
Pteranodon was a genus of flying reptile that hunted aquatic prey much like modern seabirds. Discovered in Kansas, Pteranodon has a wingspan of over 23 feet, making it larger than any bird alive today. Fossils of related pterosaurs on other continents suggest that these animals were capable of traveling long distances.
Perhaps the most interesting thing about Pteranodon is how well preserved they are in the fossil record. This wealth of evidence allows scientists to make remarkably precise discoveries about the species.
“There’s evidence of sexual dimorphism, so differences between males and females,” Zietlow said. “The females have little stubby crests, and they’re much smaller, and the anatomy of their hips is different as well.”
While efficient predators in their own right, the prowess of both Xiphactinus and Pteranodon paled in comparison to two predators lurking below the waves.
One of these predators was Megacephalosaurus. Discovered in Russell County, Kansas, this giant plesiosaur was one of the largest marine reptiles of its time.
“[Megacephalosaurus] has a skull that’s almost seven feet long. It’s nuts,” Zietlow said.
Megacephalosaurus was one of the last and largest surviving members of the Pliosauridae family. These marine reptiles began to diversify during the Middle-Jurassic period and were the most dominant ocean predators for 80 million years.
With a head longer than a man and a mouth full of bone-crushing teeth, Megacephalosaurus was a noteworthy ending to a dynasty of marine superpredators.
After Megacephalosaurus went extinct, another creature took its place as the apex predator of the Western Interior Seaway.
The state marine fossil of Kansas is Tylosaurus, a genus of mosasaur, which would have been the largest animal living in the seaway. This marine predator, which could grow up to 50 feet in length, possessed a suite of adaptations for hunting underwater.
At the front of its snout, Tylosaurus had a hardened bone structure called a rostrum, which some paleontologists believe could have been used to ram into other animals. Tylosaurus also had 72 sharp teeth, including teeth at the top of its palate. These upper teeth, called pterygoid teeth, ensured slippery prey could be swallowed whole, a terrifying fate for any unfortunate seaway animal.
When not preying upon other animals in the seaway, Tylosaurus also took the time to attack other members of its own species, with fossil evidence indicating frequent combat between Tylosaurus specimens.
“There is a Tylosaurus skull on display at the Sternberg Museum in Hays, Kansas that is loaded with bite marks that all kind of align into a V shape, like a tylosaur snout, and the neck vertebrae are preserved at kind of a funny angle,” Zietlow said. “The guess is that it had its head either ripped off or busted by another, larger mosasaur.”
Tylosaurus and its contemporaries show the unique diversity and lethality of the Western Interior Seaway.
“Even just taking the mosasaurs alone, there’s several species of mosasaurs that would coexist in this relatively small space at any given point in time, and that’s just so unlike what we see in the modern oceans and modern seaways.” Zietlow said.
The Western Interior Seaway was vast and rich, but ecosystems do not last forever. Between 80 and 40 million years ago, a geological event called the Laramide Orogeny occurred. Plate tectonics uplifted the Earth’s crust, resulting in the formation of the Rocky Mountains and causing the inland ocean to disappear.
Where there was once thousands of miles of a predator-filled ocean, there are now grasslands, temperate forests and deserts.
This land has been the site of many discoveries about the ancient beasts that once ruled North America.
Kansas in particular has contributed a great deal to the world of paleontology, providing a body of marine fossils that vastly outnumber that of their terrestrial counterparts.
“I think there’s maybe 30 T.rex in museums around the world, versus I’ve got double that in Tylosaurus,” Zietlow said.
So, next time you think about prehistoric creatures, don’t just imagine a Tyrannosaurus rex or Triceratops. There’s plenty more fish in the sea.
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