"These are incredibly rare finds — the first of their kind in the world," lead researcher Gregory Funston, a paleontologist at the University of Edinburgh in Scotland, told Live Science in an email. "Juvenile tyrannosaurs of any kind are exceedingly rare, and we've never found any bones that we suspected might be embryos, until now." The teensy, 1.1-inch-long (2.9 centimeters) tyrannosaur jawbone still sports eight little teeth. Because it was stuck in the surrounding rock, the researchers scanned the jawbone with a particle accelerator, which let them image the fossil without excavating it. Despite the jawbone's miniature size, "it looks surprisingly like other juvenile tyrannosaurid jaws," Funston said. "It has a deep groove on the inside and a distinct chin, which are both features that distinguish tyrannosaurs from other meat-eating dinosaurs." These features helped convince other paleontologists that the jawbone truly is from a tyrannosaur — "we can know that these features can be used to identify tyrannosaurs no matter how immature they are,"
