Allosaurus

The dominant predator of the Late Jurassic Morrison ecosystems, Allosaurus fragilis was a large theropod that reached roughly 9.7 meters in length, about 3.5 meters tall at the hip, and around 2,300 kilograms. Its skull carried distinctive horn-like ridges above the eyes, and its serrated, blade-edged teeth and powerful build suited it to tackling prey much larger than itself. Some fossil assemblages have been interpreted as pack hunting of sauropods, though cooperative behavior in the genus remains debated. Othniel Charles Marsh named it in 1877 from remains at Garden Park, Colorado, and it has since become one of the best-documented carnivores of the Jurassic, known from abundant material across western North America roughly 161 to 145 million years ago.