Tyrannosaurus Rex, the "tyrant lizard"—and every kid's favorite dinosaur—has been at the center of a debate over how it ate ever since fossils were first unearthed in Wyoming back in 1874. Given its morphology, there is no question that T-rex was a meat eater, but how it found its meals is an unsolved problem. Whether it was an active predator, a pure scavenger, or a mix of both, has been argued back and forth for over 100 years.
The latest research to weigh in on this issue (which is freely available to all) is published in the current issue of the Proceedings of the Royal Society B, and it concludes that T. rex "hunted like a lion, rather than regularly scavenging like a hyena." Previous studies into the hunting behavior of the T. rex have focused on morphology, a position that the authors of the current paper say is flawed. They identify two morphologically similar species, namely eagles and vultures, who have vastly divergent hunting strategies.
In their paper, the authors used an ecological model based on predator relationships in the Serengeti to determine the T. rex's hunting strategy. They conclude that scavenging would not be an effective strategy for T. rex because "it [would be] out-competed by smaller, more abundant predatory dinosaurs." The smaller dinosaurs would more often find carcasses for food (smaller therapods were predicted to be 14 to 60 times better at finding carcasses), leaving the T. rex behind at meal time. They conclude that T. rex would have ranged over large areas and have actively hunted large vertebrate prey in order to sustain their diets.
Proceedings of the Royal Society B, 2010. DOI: 10.1098/rspb.2010.2497