Artist’s rendering of limusaurusImage courtesy of Yu ChenIn a fossil first, paleontologists have discovered that a dinosaur related to the T. rex and modern birds started out life with a full set of chompers, but grew up to lose them all. In place of pearly whites, the adults sprouted a beak instead. It’s a strange metamorphosis, like an extra twisted, dinosaur-version of that nightmare where all your teeth fall out. And it’s the first time this phenomenon has ever been seen in living, dead, or extinct reptiles — which typically replace lost teeth with new ones. …