|“||Tylosaurus, a Mosasaur. That is why this place is called "Hell's Aquarium", and why we must not swim in these waters.||„|
| — Allen, describing Tylosaurus|
in Fall of a Kingdom Part I - Hell's Aquarium
Tylosaurus lived during the Late Cretaceous period, around 75-65 million years ago. While Tyrannosaurus Rex ruled over the land, Tylosaurus was at the top of the food chain in the Cretaceous seas. It shared the waters with creatures like Elasmosaurus, Xiphactinus, Squalicorax, Archelon, and Hesperornis as well as other sea creatures at the time. They died out with the dinosaurs at the end of the Cretaceous.
Tylosaurus was the largest predator in the seas of the Cretaceous. Close to shores, there would only be juveniles just over 10 feet (3 m) long. But offshore in the deep open oceans lived giant adults that measured 50 to 60 feet (15 to 18 m) in length and weighed 40 tons, making Tylosaurus the largest member of the Mosasaur family.
As the top predators of the Cretaceous seas, Tylosaurs were the dominant marine reptile of the their time. Their serpentine body shape was no accident, as they are relatives of snakes, however Tylosaurus were even much larger and far more ferocious.
Tylosaurus was an immensely dangerous ocean predator, by far the most dangerous that ever lived on planet Earth in the Cretaceous seas. And if there was anything worse than swimming with these 60-foot carnivorous sea reptiles, it would be swimming with its family. Interestingly, Tylosaurus often travel in groups to protect their offspring. They attacked and ate virtually anything that moved – sharks, turtles, giant squid, even other Mososaurs, making Tylosaurus a cannibal as well as a predator.