Tylosaurus: Cretaceous Mosasaur

Tylosaurus was a genus of marine reptile called a mosasaur that lived during the late Cretaceous Period. Contrary to popular belief, mosasaurs and other marine reptiles were not dinosaurs, even though they lived alongside them during the Mesozoic Era. The closest modern relatives of the mosasaurs are actually terrestrial monitor lizards. Fossils of tylosaurus have been unearthed in Kansas, New Zealand, The Netherlands, and Manitoba.

Tylosaurus was a large mosasaur, reaching lengths of around forty feet. The longest specimen thus far is the "Bunker Mosasaur" find that was nearly forty-five feet in length. This particular specimen was the largest mosasaur ever found in North America and one of the longest in the world. It had a long, slender body, a huge head, and a flat, eel-like tail which it used to propel itself forward in the Cretaceous Oceans. It had two paddle-like fins as forelimbs and a pair of smaller rudder-like fins in front of the tail which it probably used to help steer it through the water. The skull was around six feet long with powerful jaws and rows of mean, curved teeth. Tylosaurus probably ate whatever it could find, but most likely formed the foundation of its diet on fish and other creatures it could easily catch and swallow whole without a great deal of fuss. However, it was certainly large enough to take on larger prey, and also possessed a modified snout which would have been effective in ramming prey to subdue it. In any case, along with other large marine reptiles like plesiosaurs, it was the apex predators in the Cretaceous seas.

Tylosaurus probably preferred shallow seas to deep water due to an abundance of fish, shellfish, and sharks on which to feed. As the continents were drifting apart, many shallow waterways were forming in the Cretaceous which would have made an ideal habitat for these beasts. A large ocean called the Western Interior Seaway which split modern-day North America down the middle has been where many tylosaurus skeletons were uncovered. Because of its size, tylosaurus would have been able to exert its authority over any saltwater area it was fit to inhabit.

Tylosaurus' rule over the oceans was brief. In the same mass extinction event that wiped out the dinosaurs, so to did it overtake the giant mosasaurs. When the ecological niches emptied in the oceans, new organisms that survived the extinction would live to move into them. These turned out to be the sharks and the mammals.