By Susan Milius, Science News

An oddball fossil skull in an Oklahoma museum may represent a new kind of dinosaur, the earliest giant horned species yet found.

The 1.2-meter-long partial skull, found along with some bones, deserves to be recognized as a species in its own right, says Nick Longrich of Yale University. The specimen was originally found in 1941 in 74-million-year-old rock in northwestern New Mexico. A reconstruction currently glares down at visitors in the Sam Noble Museum of Natural History in Norman, Okla. Until now, paleontologists treated the find as a weirdly huge specimen of the Pentaceratops dinosaurs known from the Southwest region.

This beast probably weighed 6,550 kilograms, rivaling Triceratops and modern-day elephants. The head, one of the biggest of any known land animal, was an estimated 2.6 meters long. In the June Cretaceous Research, Longrich christens it Titanoceratops ouranos. The new species would add another branch of giants to the Triceratops family tree and would mean that giant size evolved some 5 million years earlier than previously thought, he says.

If Longrich is right that the giants began to diversify earlier, “It would suggest there are a lot of undiscovered horned dinosaurs sitting around out there,” says Andrew Farke of the Raymond M. Alf Museum of Paleontology in Claremont, Calif.

The skull discovered in 1941 spent 54 years in museum storage before researchers cleaned and prepared it for display by filling in missing parts, assuming it was a species of Pentaceratops.

Now, Longrich says he has looked at the fossil in a new light. Comparing traits across horned dinosaurs, he found that the skulls’ outsized nostrils, the position of its nose, some of the cavities inside its skull and many more features resemble not Pentaceratops but those of the Triceratops and Torosaurus giants. In scoring dozens of traits, overall the fossil looked like an early relative of those giants, he concludes.

The specimen has been “problematic,” Farke acknowledges. “Right now, I’m skeptical but convincible on the validity of Titanocerotops,” he says. For the moment, he is inclined toward the alternative view that the fossil is what it was originally thought to be: an outsized individual of the not-particularly-titanic Pentaceratops. Differences between the specimen’s bones and those of the smaller Pentaceratops could have developed while growing to such a huge size, Farke says.

John Scannella and Denver Fowler at the Museum of the Rockies at Montana State University in Bozeman also consider the specimen a big adult Pentaceratops. “If you do find a mature form it will likely look different from preceding growth stages—we see this in every growth series that has been described for a dinosaur,” Scannella says.

Mistaking dinosaurs at different stages of growth for different species may be a widespread problem, says Jack Horner, also at the Museum of the Rockies. “I think most of the dinosaur specimens we find represent subadult sizes,” he says. He and Scannella last year argued that what’s now considered the species Triceratops is just a younger growth stage of a different horned dinosaur, Torosaurus.

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