Tyrannosaurus rex primarily ate herbivore dinosaurs, including the Edmontosaurus and the Triceratops. Studies suggest that the Tyrannosaurus rex also practiced cannibalism. Paleontologists believe that if two Tyrannosaurus rex dinosaurs fought to the death, the winner would eat the loser, based on bite marks found on Tyrannosaurus bones.
Paleontologists disagree as to whether the Tyrannosaurus rex was more a hunter or a scavenger. Tyrannosaurus rex's binocular vision, a trait found mainly in predators in the modern-day animal kingdom, indicates that it was indeed a hunter. In addition, healed bite marks in other dinosaur fossils indicate that Tyrannosaurus assaulted living prey. A 2007 study determined that the Tyrannosaurus rex hit a top running speed of 18 miles per hour, faster than many of the smaller dinosaurs on which the Tyrannosaurus preyed.
However, scientists theorize that unlike carnivores of today, Tyrannosaurus rex did not hunt in packs. It was a solo hunter that did not enjoy sharing its food. Some paleontologists believe that this made it difficult for Tyrannosaurus to find enough food to survive, and also that it made the dinosaurs vulnerable, forcing them to become scavengers. This theory supports the idea that not only did Tyrannosaurus rely on live prey, but opportunistically feasted on already-dead food as well.