dailyfossil: Tylosaurus
When: Late Cretaceous (90 - 80 million years ago)
Where: Swam mostly though what is now the great plains region of North America, with the best fossils to date found in Kansas.
What: Tylosaurus is a giant lizard. No really! It is a mosasaur, which were a group of marine predatory lizards that swam the warm seas of the late Cretaceous. Mosasaurs as a whole are most closely related to varanids (monitor lizards, including the Komodo Dragon) within Squamata and are the biggest lizards to have ever existed. Tylosaurus was one of the largest mosasurs, estimated to have reached over 50 feet (~15 meters) long. It’s skull alone was roughly 5 feet in length! It was an apex predator, feeding on anything and everything it could snap between it’s giant jaws. A specimen has been found that had plesiosaur remains inside its ribcage.
This humongous beast swam though the Cretaceous Seaway aka the North American Inland Sea. This was a huge, warm, shallow sea that ran north-south though North America during the latter half of the Cretaceous, splitting the landmass in half. The sea was over 600 miles (~1000km) wide, almost reaching from the Rockies to the Appalachian mountains, and is estimated to have been 2,500 feet (800 meters) deep, which is relatively shallow for such a large body of water. Tectonic activities near the end of the Cretaceous caused this sea to vanish as quickly as it formed, resulting in the extinction of giants like Tylosaurus.
