From birth to adulthood, T. rex took 40 years growing into an eight-ton giant, and scientists think that long childhood helped it dominate the dinosaur world

For most Americans, Tyrannosaurus rex is the ultimate symbol of prehistoric dominance: massive, fearsome, unstoppable. But science just threw us a curveball: the king of the dinosaurs was in no hurry at all to become one.

According to a new study titled ‘Prolonged growth and extended subadult development in the Tyrannosaurus rex species complex revealed by expanded histological sampling and statistical modeling’ published in PeerJ by paleontologist Holly Woodward of Oklahoma State University and colleagues, T. rex likely grew to its adult size of about eight tons in about 40 years. That's some 15 years longer than scientists had previously believed, and it's among the most detailed reconstructions of T. rex growth ever attempted.