Scannella said he and Horner tried for three years to look for alternative explanations for their findings. Some undergraduates also helped prepare the fossils once they were brought back to the Museum of the Rockies.

Many undergraduate students, as well as volunteers from around the world, participated in the project by discovering and excavating the Triceratops specimens in the field. Even in Triceratops that were previously considered to be adults, the skull was still undergoing dramatic changes. Microscope studies revealed that the tissues of Torosaurus specimens are more heavily remodeled than those of even the largest Triceratops, strongly suggesting that Torosaurus specimens are in fact adult Triceratops, Scannella said. They examined the microstructure, surface textures and shape changes of the frills. Scannella and Horner measured the length, width and thickness of the skulls. The paleontologists also examined skulls from several North American institutions, including the American Museum of Natural History in New York, the National Museum of Natural History at the Smithsonian Institution in Washington, D.C., and the Peabody Museum of Natural History at Yale University in New Haven, Conn. More than 30 were skulls that came out of the Hell Creek Formation and are housed at the Museum of the Rockies. Scannella and Horner examined more than 50 Triceratops specimens for their study. 'It is possible that mortality was fairly high for Triceratops before they reached their fully mature morphology.' 'If Torosaurus is actually the mature form of Triceratops, we must ask why вЂ›Torosaurus' specimens are relatively rare compared to Triceratops,' Scannella said. When the paleontologists did find 'Torosaurus' skulls, the skulls were all large. None of the Torosaurus specimens came from immature animals, Scannella said. 'Torosaurus' specimens are much rarer than Triceratops, however. Other skulls are the size of a small car. Some of the skulls belonged to juvenile Triceratops and roughly the size of footballs. Forty percent of the specimens came from Triceratops at different stages of growth. As part of the study, field crews collected hundreds of specimens. Led by Horner, the large-scale project was conducted to reconstruct the ecosystems that existed during the Cretaceous Period that ended about 65 million years ago when there was a mass extinction of dinosaurs. Scannella and Horner benefited from an extensive 10-year study of the Hell Creek Formation in Eastern Montana. '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. The Triceratops study suggests that it is critical that paleontologists consider ontogeny (growth from a juvenile to an adult) as a source of major morphological variations before naming new species of dinosaurs to account for variation between specimens, Scannella added. In order to get the complete story, you need to have a large sample of fossils from many individuals representing different growth stages.' 'We have to put together the story based on fossils. 'Paleontologists are at a disadvantage because we can't go out into the field and observe a living Triceratops grow up from a baby to an adult,' Scannella said. 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. They looked very different, and their skulls changed radically as they matured. The confusion over Triceratops and Torosaurus was easy to understand, Scannella said, because juvenile dinosaurs weren't just miniature versions of adults. Scannella is a doctoral student in earth sciences, and Horner is Regents Professor of Paleontology at MSU's Museum of the Rockies. The Journal of Vertebrate Paleontology is the official journal of the Society of Vertebrate Paleontology. They added that the discovery contributes to an unfolding theory that dinosaur diversity was extremely depleted at the end of the dinosaur age. MSU paleontologists John Scannella and Jack Horner said in the July 14 issue of the Journal of Vertebrate Paleontology, however, that Triceratops and Torosaurus are actually the same dinosaur at different stages of growth. Triceratops had a three-horned skull with a rather short frill, whereas Torosaurus had a much bigger frill with two large holes through it. Since the late 1800s, scientists have believed that Triceratops and Torosaurus were two different types of dinosaurs.

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