Greg got permission to cut open the bones of several different T. rex skeletons, along with many other close tyrannosaur relatives like Albertosaurus and Gorgosaurus. Shockingly, not a single bone had more than thirty growth rings. That means tyrannosaurs matured, reached adult size, and died within three decades. Big dinosaurs like T. rex didn’t grow slowly for many decades (or centuries) but must have reached their huge sizes by growing rapidly for a much shorter period of time.
