During the late Jurassic period around 150 million years ago, a small tyrannosauroid called Stokesosaurus lived in North America. This tiny carnivore had to keep an eye out for the much larger Allosaurus while hunting and scavenging.
But by the late Cretaceous period, around 66 million years ago, Allosaurus was long gone and tyrannosauroids had evolved into hulking, ferocious top predators. Case in point: the infamous Tyrannosaurus rex.
For many decades, scientists could not find any North American tyrannosauroid fossils between these two periods. It was as if these dinosaurs had disappeared in the late Jurassic and reappeared larger and more ferocious 84 million years later.
