Tyrannosaurus rex evolved in North America, but its direct ancestor came from Asia, crossing a land bridge connecting the continents more than 70 million years ago, according to a new study led by UCL researchers. The study, published in Royal Society Open Science , also found that the rapid growth in size of tyrannosaurids (the group that included the T. rex ) as well as a closely related group called megaraptors coincided with a cooling of the global climate following a peak in temperatures