There were three of them, one of them probably a child, and at least one met a gruesome end at the hands of a terrifying predator.
About 67 million years later, a Wyoming rancher led scientists to their remains. Now experts are digging out one of the most complete skeletons yet of a Triceratops, the three-horned, plant-eating dinosaur that was one of the last of the giant reptiles.
"There's only three other skeletons that will match the completeness of one of the specimens we're excavating right now," said paleontologist Peter Larson, president of the Black Hills Institute of Geological Research.
Most of the remains found before now have included fewer than half of the prehistoric creatures' bones, Larson said Monday. The most complete to date, now on display at the Houston Museum of Natural Science in Texas, has about 76% of its skeleton.
"The largest, more mature individual appears to be the most complete," Larson said. "One is just a bit smaller, and there's another one that by live weight is probably only half the size."
The dig is going on near Newcastle, Wyoming, more than 200 miles north of Cheyenne.
"The fact that there are three of them together is really cool," Larson said. The trio could be male and female and their young, or they could be two females looking after a juvenile dinosaur, he said. And before now, there was no indication that the Triceratops moved in groups.
The Black Hills Institute is working with the Naturalis Biodiversity Center, from the Netherlands, on the dig. Larson called the discovery of a young Triceratops a "very significant" find as well, since it will give scientists an insight into how the great lizards grew up.
Triceratops lived in the twilight of the Cretaceous Period, about a half a million years before the dinosaurs' extinction. Much of what is now the Great Plains and southern Canada was once part of a vast inland sea, and the region is rich in fossils.
"Like most of the specimens that were found, it was brought to our attention by a rancher," Larson said. The rancher sent photos to the Black Hills Institute, located in neighboring South Dakota, in late 2012. Excavation began in May and is expected to take about a month.
So far, the bones that have turned up point to a violent end, probably at the hands of the feared Tyrannosaurus rex. On the largest of the three specimens, at least two of the major limb bones were "bitten through," Larson said.
"If you can imagine, this is a bone that is nearly four feet long," he said. But a T.rex "would kind of chop the carcass up with their giant, shearing jaws," ripping through flesh and bone alike.
"I think we also have a feeding site for Tyrannosaurus rex, which is very exciting," he said. "This is potentially a site where we can learn the behavior of two different species."
-- CNN's Janet DiGiacomo contributed to this report.
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