UCMP's Mark Goodwin and Jack Horner, curator of paleontology at the Museum of the Rockies, have been working in the late Cretaceous Hell Creek Formation of Eastern Montana for decades, an area famous for its impressive fossil assemblages including fish, mammals, and dinosaurs like Tyrannosaurus rex.
Based on a census of predator and prey found at several of the time intervals represented in the Hell Creek Formation, Goodwin and Horner concluded that T. rex was far too abundant to be a lion-like top predator. Top predators are usually one-third or one-fourth as abundant as their prey due to their larger energetic requirements. Opportunistic carnivores like hyenas, however, can number twice that of top predators. With the results of their census and no evidence that T. rex was an extra picky or capable hunter, the scientists suggest it likely subsisted on both live and dead animals, exploiting a variety of food sources like the hyena.
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