Billions and billions of tyrannosaurs walked the Earth Scientists arrived at the estimate by using calculations based on size, metabolism, and the populations of animals today. Social Sharing CBC Radio · Posted: Apr 23, 2021 5:17 PM ET | Last Updated: April 23 Over approximately 2.5 million years, North America was likely home to 2.5 billion Tyrannosaurus rexes. Less than 100 have been dug up and studied by paleontologists, according to a UC Berkeley study( Image by Julius Csotonyi, courtesy of Science magazine)