Brace yourselves. The famous triceratops dinosaur never actually existed as a separate dinosaur species, paleontologists say.

Known for its three horns and the bony, frilled ridge around its head, the triceratops was most likely just a younger version of the rarer torosaurus, say researchers John Scannella and Jack Horner at the Museum of the Rockies in Montana.

The species were very similar. Both had three horns and each had the distinctive head frill that makes the triceratops famous. But in the torosaurus the horns and ridge were shaped differently, with the ridge appearing smoother and thinner. It also had two holes....