On land, the Tyrannosaurus rex was one of the most scary apex predators to roam the Earth. In the ocean, that title belongs to the Tylosaurus. This late Cretaceous sea monster grew to almost 50 ft (15 m) long and had a long mouth of razor-sharp teeth. It lived in the Western Interior Seaway, now known as Kansas in the United States. It was a carnivore that ate everything that moved, including other mosasaurs!
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Some Quick Facts about the Tylosaurus

Name | Tylosaurus (meaning “knob lizard” or “nose lizard”) |
Type of dinosaur | Mosasaur |
Territory | Ocean regions, North America |
Size | 35-50 feet long, |
Color | Gray |
Interesting Characteristics | Large crocodile-like snout, body covered in hard scales |
Diet | Marine life, Elasmosaurus, Plesiosaurs |
Major Threats | Mosasaurus |
The Tylosaurus was a late Cretaceous sea creature that grew to be almost 50 feet long! With a mouth of razor-sharp teeth and strong flippers for swimming, all other sea creatures knew better than to mess with this ferocious apex predator.
Where did the Tylosaurus live?
The Tylosaurus lived in shallows parts of the ocean, but it was discovered in Kansas. In North America, Kansas is miles and miles away from the sea. So how can this be?
One hundred fifty million years ago, the Earth looked very different. The oceanless plains of Kansas in the interior of the United States were once covered by an ancient body of water called the Western Interior Seaway. And that’s precisely where the ferocious Tylosaurus lived.
Did the Tylosaurus Have Any Predators?
No, the Tylosaurus did not have any predators, unlike the tiny Microceratus on land. Think of this sea monster like the Tyrannosaurus rex of the ocean. It was one of the most enormous carnivorous sea creatures of the late cretaceous period, and all of the land and sea animals knew better than to mess with this colossal beast.
However, there was one predator that the Tylosaurus needed to keep an eye out for: other Tylosauruses. This apex predator would attack anything that moved, including other Tylosauruses! While they would fight with each other, likely over territory, scientists have found no evidence that these scary Cretaceous sea creatures were cannibals (or ate fellow Tylosauruses).
What did the Tylosaurus Eat?
The Tylosaurus was an excellent hunter and ate anything from fellow sea creatures, fish, and even pre-historic seabirds, like the Hesperornis. By studying the stomach contents of Tylosaurus specimens, paleontologists discovered that the Tylosaurus ate things like other mosasaurs, plesiosaurs, seabirds, fish, and small reptiles. If it lived in the sea, it was at risk of being a tasty treat for this scary apex predator.
They crept in the shadows of the ocean, silently waiting for dinner to arrive. When Tylosaurs spotted their prey, they propelled forward with their solid flippers and stunned their target by ramming them with their long, pointed snouts. This way of hunting is very similar to modern-day whales.
What Is the Difference Between a Tylosaurus and a Mosasaurus?

A Mosasaurus is a type of sea creature, like how a sauropod is a type of dinosaur. Mosasaurus refer to large, marine replies under the Squamata classification (similar to snakes and lizards). Think of Mosasaurus as the genus and Tylosaurus as the type of dino in that category.
The Tylosaurus wasn’t the only member of the Mosasaurus family. Cretaceous sea mosasaurs include Platecarpus, Clidastes, Halisaurus, Plotosaurus, and Ichthyosaur. Of those dinosaurs, the Tylosaurus was the largest Mosasaur in the Western Seaways and would often eat other Mosasaurs as dinner.
When Was the Tylosaurus Discovered?
Othniel Charles Marsh discovered the Tylosaurus in 1868 in Gove County, Kansas. It was the third type of Mosasaur found in North America, alongside the Clidastes and Platecarpus. The initial fossils records of the Tylosaur were incomplete and didn’t provide a good picture of this pre-historic sea creature.
However, as more fossils are uncovered in the American Midwest, paleontologists learn more and more about this fascinating specimen. A near-complete fossil discovered in Kansas showed the contents of its belly. What was inside its stomach, you ask? It was a Plesiosaur!