But it wasn't until the late 1980s that Currie and others were able to investigate the area.
What the scientists found was shocking—one of the richest bone beds in the world, with over 300 bones per cubic meter (35 cubic feet).
In just 3 to 5 percent of the bone bed, scientists found 15 skulls and 27 individuals of varying ages.
"Most dinosaur species are known from one or two typically incomplete specimens, whereas this species is from a massive bone bed that preserved the remains of dozens of individuals and a number of skulls, sampling it from juvenile to adult and showing us the real variation that occurs among a species," said the Utah museum's Sampson.
The group found large differences between young and old among these Triceratops relatives. The juveniles seemed to have been relatively smooth-faced, while the adults were spiky, Currie, the lead scientist, explained.
"It was the first really good example showing growth and variation in these animals, where we had the babies looking one way and the adults looking totally different," Currie said.
An Important Ancestor
Pachyrhinosaur, which dates to the Late Cretaceous period (145 million to 65 million years ago), is also an essential link in the evolutionary chain of horned dinosaurs of North America, he said.
(See related news photo: Triceratops' "Granddaddy" Discovered in Canada [March 5, 2007].)
"It's part of a sequence where we can look at not only the animal itself but all its close relatives, and we're reaching the point now where we can trace these things from formation to formation and see the evolutionary changes of the lineage," Currie said.
Sampson added that the new research stands to make a significant advance in the study of horned dinosaurs.
"This particular [study] is undoubtedly the most detailed description of a horned dinosaur ever done, and even one of the most detailed description of any dinosaur ever," Sampson said. "It's a landmark."
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