The dinosaur bones dug up by a bulldozer in Thornton in August 2017 could change how science views late Cretaceous dinosaurs. Paleontologist Joe Sertich, curator of dinosaurs for the Denver Museum of …
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The dinosaur bones dug up by a bulldozer in Thornton in August 2017 could change how science views late Cretaceous dinosaurs.
Paleontologist Joe Sertich, curator of dinosaurs for the Denver Museum of Nature and Science, said he and his staff first thought the bones belonged to an adolescent Triceratops because of the fossil’s thinner leg bones.
A month of work with the fossil determined the bones belonged to a much rarer Torosaurus — an animal similar to Triceratops but with a smaller nose horn and a more delicate frill shield on the back of its head.
“There is an active hypothesis among certain paleontologists that a Torosaurus is a fully grown adult Triceratops,” Sertich said.
The working theory has been that Torosaurus like the Thornton fossil were elderly Triceratops, as evidenced by the more delicate frill shields. While the frill on a Triceratops is thicker and sturdy, the theory said it grew weaker and thinner as the animal got older, eventually developing holes.
“What we are seeing with this specimen is that there are differences that show that they are distinct, the Torosaurus was it’s own specific species and is actually quite different,” he said.
He compared the two to elk and a deer, co-existing in the same environment.
“That’s what’s really cool,” he said. “Now that we can see these differences, it might show us that they ate different things or that their ecology was different.”
Sertich and his team have finished cleaning the fossil — dubbed “Tiny” by students at Thornton’s Brantner Elementary which is near the site where the bones were found — and have sent it off to an expert to have casts made. When they come back, they ‘ll be available for public display — at the museum or elsewhere.
“Hopefully we can get copies out in the community,” Sertich said. They haven’t decided where yet.
“That’s what we’re trying to figure out,” he said. “We can loan them, or we’d love to get one into the hands of Thornton’s school district if we could.”
A bull dozer driver preparing the site at 132nd and Quebec for new public safety substation hit the first bone Aug. 25, 2017 and immediately stopped work, contacting his supervisors and then the museum.
Museum staff arrived at the site Aug. 28 and began digging, uncovering hundreds of bones and bone fragment and happily showing them off to local and national media.
Cleaning efforts also revealed several more skull bones and a complete tibia. An estimated 98 percent of the skull and at least 20 percent of the skeleton have now been identified.
Sertich said it’s likely the animal died and was set upon by scavengers, including tyrannosaurs and smaller dinosaurs. That theory was bolstered by the find Sept. 7 of a banana-sized T-Rex tooth mixed among the Torosaurus bones.
“What’s really unique about this find is just how well preserved it is,” he said. “It’s the most complete Torosaurus, about 98 percent of the skull is complete. We are only missing two small skull bones and the preservation has left it un-distorted. It’s exactly like it would have been in life.”
Triceratops are most common dinosaur fossils around, and Sertich said they were common in the Midwestern plains, especially in northern U.S. states like Montana and North Dakota. The museum’s collection includes a 2003 Triceratops fossil from Brighton as well as the Highlands Ranch specimen uncovered last year. That one is following the same process as the Thornton Torosoros, just few months behind.
“It’s still being cleaned up in our lab, so there’s not much to look at there,” he said.
Cleaning involves delicately picking the bone apart from the stone and soil, using smalls dental tools, water, toothbrushes and pneumatic tools.
“We have to consult constantly among our team to make sure we are doing it right,” he said. “This one (the Thornton fossil) took about 16 months to get fully cleaned, and then another ten months for molding and casting. And now we’re in the research phase.”
Research on the fossil could continue for years.
“This one of about 12 Torosaurus specimens in the world,” he said. “Most are about 50 percent complete, and there have been reconstructed Torosaurus skulls that drew upon Triceratops. Those look a lot like a Triceratops.
“But what we are learning is that they are really quite different. The face has different proportions, so it’s not just the frill that is different.”
The frill itself is too thin to be useful for defense.
“It would have been reinforced with sub-tissue, so there would have been membranes and cartilage and likely a keratin, like a fingernail, coating on top,” Sertich said. “But still it was huge and thin.”
There’s no way of determining the sex of the animal, he said.
“Unless it has eggs inside, you can’t tell if it’s a male or female, and we didn’t find any eggs,” he said. “So Tiny’s sex is undetermined.”
Both species of animals lived at the same time, roughly 66 million years ago just before the Late Cretaceous “extinction event” and were likely distant cousins.
“It was at the end of the Cretaceous, so these were the last dinosaurs that lived here in the Rocky Mountain West,” he said. “Within a few 1,000 to 100,000 years of these guys, dinosaurs go extinct.”
His team is also working on a series of fossils found in Colorado Springs from October. Those fossils come just after the dinosaurs and include early mammals.
“These are on the dinosaur side, and the ones in Colorado Springs are the ones that thrived right after Tiny and the Tyrannosaurs, right on the other side of the extinction event,” he said.
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