Tylosaurus was among the largest mosasaurs on record. At around 30-40 feet in length and over 5-7 tons. These huge carnivores were the alpha predators of their time and location. Tylosaurus had a skull nearly 4 feet long and dozens of razor sharp teeth. Like other mosasaurs, the closest living relatives of Tylosaurus are monitor lizards, though mosasaurs were fully aquatic and many times the size of their terrestrial cousins. Tylosaurus lived in the Western Interior Seaway of North America some 75-85 million years ago.