Scientists thought this fossil was a teen T. rex. Turns out it's a new tyrannosaur

It's known as the "Dueling Dinosaurs" fossil: A triceratops and a tyrannosaur, skeletons entangled, locked in apparent combat right up until the moment of their mutual demise.

Even in the Hell Creek Formation in eastern Montana, a spot known for great finds, this specimen was, in a word, "fantabulous," says Clayton Phipps , a self-described rancher, cowboy and dinosaur hunter.

That discovery in 2006 now appears to have overturned decades of dinosaur dogma about Tyrannosaurus rex , the fearsome giant long thought to be the sole top predator stalking the late Cretaceous. In a paper in the journal Nature , paleontologists Lindsay Zanno and James Napoli conclude that some of the bones from that specimen belong not to a teenage T. rex , but to a fully grown individual of