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.
There are some animals on earth that can be traced back to the Mesozoic Era when dinosaurs walked the earth; these animals include monotremes such as the duckbill platypus, reptiles such as the crocodilians and sea creatures such as the sea urchin. For the most part, the animals that are alive today have made evolutionary changes from the forms they had when dinosaurs were alive. For example, though the event that caused dinosaurs to die out also killed many other reptile species, several surviving reptile species have direct ancestors from that era, including the crocodilians, which are smaller than their Mesozoic ancestors.