T. rexes walked the Earth during its existence, reports Karina Shah for New Scientist. The new study was published this week in the journal Charles R. Marshall, a University of California, Berkeley paleontologist, was fascinated with the idea of how many of the mega-predators walked the Earth whenever he held a T. rex fossil, reports the New York Times. “Were there are a million, a billion, a trillion T. rexes? Is this one in a million, one in a billion, one in a trillion? How on earth could we know that number? We all know fossils are rare, but how rare are they? And so it really started with that question,” Marshall tells the