TRICERATOPS AND TOROSAURUS: SAME DINOSAUR

Two dinosaurs became one this week, as paleontologists have just discovered that the dinosaurs previously known as Triceratops and Torosaurus are actually the same species.

(The classic image of a Triceratops is on the left, while the new face of Triceratops, previously calledTorosaurus, is on the right. Artwork by Holly Woodward, Montana State University)

 

For over a century, scientists thought Torosaurus was a unique species. It was characterized as having a huge frill, bigger than that of Triceratops, with two large holes in it. But Montana State University paleontologists John Scannella and Jack Horner now say the excavated Torosaurus remains were justTriceratops at different growth stages.

The findings are published in the latest issue of the Journal of Vertebrate Paleontology.

(John Scannella works on a Triceratops fossil found north of Jordan, Montana, on the Hell Creek Ranch. Photo by Lon Bolick.)

 

Scannella thinks the confusion is understandable, because juvenile dinosaurs weren't just miniature versions of adults. According to an MSU press release, they looked very different, and their skulls changed radically as they matured. Recent studies have revealed extreme changes in the skulls of pachycephalosaurs,tyrannosaurs and other dinosaurs that died out about 65 million years ago in North America.

"Paleontologists are at a disadvantage because we can't go out into the field and observe a living Triceratopsgrow up from a baby to an adult," Scannella said. "We have to put together the story based on fossils. In order to get the complete story, you need to have a large sample of fossils from many individuals representing different growth stages."

(Jack Horner and team arrive at the Hell Creek Ranch to excavate a Triceratops. Photo: Lon Bolick)

 

In future, Scannella hopes paleontologists will consider ontogeny (growth from a juvenile to an adult) before jumping the gun and announcing the discovery of a "new" dinosaur species.

"Without considering changes in shape throughout ontogeny, we overestimate dinosaur diversity and hence produce an unrealistic view of the paleoecology of these animals," Scannella said.

Thanks to the plethora of dinosaur remains at the Hell Creek Formation in Eastern Montana, he and Horner were able to study hundreds of specimens, 40 percent of which came from Triceratops at different stages of growth. Some Triceratops skulls were the size of footballs, and belonged to juveniles, while others belonging to adults were about the size of a small car. Analysis of the microstructure, surface textures and shape changes of the dinosaur individuals' frills revealed that the "Torosaurus" and Triceratops fossils came from the same species.

(John Scannella conducting field work in Ferron Sandstone. Photo: Jeannette Wolak)

 

The finding that Torosaurus was a grown-up Triceratops adds fuel to the theory that dinosaur diversity at the end of the Cretaceous Period and Mesozoic Era was far less than previously thought, Scannella believes."A major decline in diversity may have put the dinosaurs in a vulnerable state at the time when the large meteor struck the Earth at the end of the Cretaceous Period," Scannella explained. "It may have been the combination of the two factors -- lower diversity and a major global catastrophe -- that resulted in the extinction of all the non-avian dinosaurs."