Tylosaurus was a ferocious marine lizard that powered itself through the water with sweeping motions of its long body and fish-like tail. At a massive 46 ft long, it was about the size of a humpback whale and one of the largest mosasaurs. It lived in the Western Interior Seaway of North America during the Late Cretaceous, from about 75 to 85 million years ago. History: The first Tylosaurus remains were discovered in the 1860s after the American Civil War. The first specimen was described by Edward Drinker Cope in 1869 as Macrosaurus proriger. Hot on his heels in 1870, Cope'rival, Othniel Charles Marsh, began the first fossil hunting expeditions of Yale College. These uncovered more fossils of this ancient marine reptile. In 1872 Marsh created the name Tylosaurus, which means knob (or snout) lizard, in reference to the elongated bony muzzle that projects beyond the last teeth in the upper jaws. Scientific Name: Tylosaurus proriger Characteristics: The predato