Meet what could be the new granddaddy of horned dinosaurs—Titanoceratops.
At 15,000-pound (6,800-kilogram) the prehistoric titan would have rivaled the African elephant-size Triceratops, which weighed more than 11,000 pounds (5,000 kilograms), according to a new analysis of a partial skeleton.
The beast—which had an 8-foot-long (2.4-meter-long) skull—is the biggest dinosaur found so far in North America during the late Cretaceous period, about 74 million years ago.
(Read about another Triceratops ancestor found in Canada.)
If indeed a new species, Titanoceratops' discovery could also mean that triceratopsins—members of a family of giant horned dinosaurs—evolved their gigantic sizes evolved at least five million years earlier than previously thought, the study says.
Triceratops would have evolved into a separate species after Titanoceratops had died out, according to the study.
"It's pretty surprising—I would have not have thought something this big and this advanced was living in this time period," said study leader Nicholas Longrich, a paleontologist at Yale University.
But other experts say the skeleton is not complete enough to call it a new species.
"I would like it to be real," said Michael Ryan, curator of vertebrate paleontology at the Cleveland Museum of Natural History.
"[But] until we find a better specimen ... there's no reason to say it isn't a Pentaceratops," a similar type of horned dinosaur.
A More "Graceful" Triceratops?
The partial skeleton was found in New Mexico in 1941 and stored until 1995, when it was reexamined and identified as an "exceptionally large" Pentaceratops, according to the study.
But when study leader Longrich recently looked at the skeleton, he found 20 physical differences between the skeleton and Pentaceratops.
For instance, many of these disparities are "classic" Triceratops features—such as the shape of the nose and monstrous, forward-curving horns. This suggested to him that the animal was not Pentaceratops, but rather a new Triceratops ancestor. (See more pictures of dinosaurs that lived during the Cretaceous.)
Titanoceratops, Longrich said, would have looked like a more "graceful" version of Triceratops, with a longer nose, slightly bigger horns, and a thinner frill—a fan-like bone covering its neck.
Another convincing piece of evidence to Longrich is the specimen's size: It was twice as big as any known Pentaceratops, of which there are about six good specimens.
"In my opinion there are far too many differences for this to be another Pentaceratops," he said.
Dinosaur Skeleton Missing Key Indicators?
But the Cleveland museum's Ryan said that the skeleton doesn't look that different from Pentaceratops.
For one thing, he said, many of the 20 differences outlined by Longrich are not diagnostic, and that they don't reveal for sure that the animal is another species.
For another, he said, the incomplete specimen is missing the most crucial part of a horned dinosaur, at least for paleontologists' research: the back of the frill.
"That's where most of the key characters for horned dinosaurs are included," he said.
"The frill would be very helpful, since the parts of it illustrated don't seem to me to be outside the probable variation in Pentaceratops."
For instance, Ryan suspects the specimen may just be a particularly elderly—and thus bigger—Pentaceratops, which are usually difficult to find in the fossil record simply because older dinosaurs were rarer.
But study co-author Longrich said that there are at least two known specimens of elderly Pentaceratops that are a lot smaller than, and do not resemble, what he believes is Titanoceratops.
Longrich added, "The fact that we're missing part of the frill is a little annoying, but it doesn't really affect things that much."
"And we actually have some pieces of the frill, and they don't really look much like Pentaceratops."
New Dinosaur "Reasonable Possibility"
Overall, the "great bane" of paleontology is finding out why there's variation in a sample, Thomas R. Holtz, Jr., a vertebrate paleontologist at the University of Maryland, said via email.
For instance, with so few horned-dinosaur specimens, it's hard to tell if an odd fossil represents a variation within a species' growth, due to regional differences, or between sexes—or because the fossil actually represents a distinct species.
But Longrich's hypothesis that the skeleton represents a new type of dinosaur—and not just a "big ass" Pentaceratops—is "certainly a reasonable possibility," said Holtz, who was not part of the new research.
"After all, Triceratops must have had ancestors in this earlier time, and this individual does show specialized traits that we see in the Triceratops complex."
Meanwhile, study leader Longrich hopes another dinosaur will be found with a more intact frill. "I would love to see another one—that would be the nail in the coffin."
Titanoceratops research to appear in an upcoming issue of the journal Cretaceous Research.