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

toggle caption Anthony Hutchings/Friends of the NC Museum of Natural Sciences

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 a different tyrannosaur species — Nanotyrannus lancensis.

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The majority of paleontologists, after some debate, had dismissed the idea that any other tyrannosaurs existed besides T. rex. And yet, the sands of Montana seem to have disgorged a second one. In a broader analysis of other fossils, the two researchers also uncovered what they say is a third tyrannosaur species, form