Among fossil hunters, the Hell Creek Formation is legendary for the treasures it holds. Ranging from 50 to 180 meters deep, it runs from Montana through the Dakotas to Wyoming, with fossils dating from 66 million to 68 million years ago, in the late Cretaceous period. Most of the world’s Tyrannosaurus rex finds hail from there. This summer, a team including representatives from the Burke Museum and the University of Washington dug up something remarkable from the Hell Creek Formation: fossils from four dinosaurs, including a potential new species.

The four discoveries included the ilium (hip) bones of an ostrich-sized theropod (the group of two-legged dinosaurs covering T. rex and raptors); the hips and legs of a duck-billed dinosaur; the pelvis, toe claw and limbs from a second theropod that could be a rare Anzu — which has been called the “Chicken from Hell— or a new species; and a triceratops specimen including a well-preserved skull and bones still being uncovered.

Three of the four were discovered near each other on Bureau of Land Management land leased to a rancher, and the possible Anzu was found on a wildlife refuge managed by the U.S. Army Corps of Engineers.

All four dinosaurs will be held in trust for the public on behalf of the Bureau of Land Management and become a part of the Burke Museum’s collections. Right now, the public can watch paleontologists uncover the discovered dinosaurs as they remove the surrounding rock, through the Burke’s open-view lab, starting with the theropod hips. The triceratops, which is expected to be fully excavated in summer 2022, will not be available yet. 

Greg Wilson Mantilla, Burke Museum curator of vertebrate paleontology and UW biology professor, reunites with the Hell Creek Formation every summer — and has done so for over 20 years, since he was a student.


Today he leads the Hell Creek Project, a research collaboration of paleontologists from around the world studying life right before, during and after the Cretaceous-Paleogene mass extinction event that killed off all dinosaurs except birds, as well as an educators’ Discoveries in Geosciences (DIG) Field School program. 

The excavation this summer that unearthed many of the fossils in this recent find included scientists, volunteers and students from the UW and other schools, all drawn together to uncover mysteries from over 60 million years ago.

Fossil market heats up

Over the years, fossil digging has gotten more popular and more complicated.

The Hell Creek Formation’s reputation as a fossil mecca draws numerous scientists and students, tourist groups and amateur fossil hounds, not to mention professional fossil hunters.

Fossil hunters are lured by increasingly spiking prices fetched by fossils at auction or on the underground market. In 2020, a nearly 40-foot-long T. rex skeleton named Stan sold at auction house Christie’s for $31.8 million — the biggest price tag for a single fossil ever. Now in a private collection, some scientists say such sales increase inequity of access for public education and stop research from being done on that specimen.

A decade ago, charging by the inch, a single T. rex tooth would fetch $1,000; now that price is $4,000, according to Bloomberg. As a result, museums find themselves competing with private collectors at auctions.


This increased competition makes it harder for scientists and museums to find, study and display these pieces of biological history, making the Burke’s recent acquisition all the more significant. The Burke doesn’t have to pay for the fossils, though it pays for the equipment and associated costs to do the excavations.

On the discovery side, U.S. law cedes fossils discovered on private property to landowners, some of whom refuse to allow digging. For the dig this summer, Wilson Mantilla applied for permits from the Bureau of Land Management and the Corps of Engineers, and received permission from the rancher to whom some of the land is leased.

“What are we going to find today?”

Over the years, Wilson Mantilla has become familiar and formed crucial relationships with the residents, scientists and fossil hounds of Hell Creek Formation, like Judith and Bruce Wake.

The Wakes are paleontology enthusiasts from Missouri. At 76 and 84, they’ve been coming to the Hell Creek Formation since 2002 and, as volunteers, have found fossils from close to 200 kinds of dinosaurs and amphibians. Their downstairs has become “a museum” of collections that they bring out to show elementary classes and that will eventually be donated for education.

Out in Montana, if they find something promising, they ask Wilson Mantilla to verify it. When he has a lead, he asks them to check if it merits pulling an excavation permit. They call it “prospecting.” 

In 2019, the Wakes found the theropod ilium and the duck-billed dinosaur hindquarters that were excavated this summer.


If it’s raining, work grinds to a halt — the local bentonite clay turns roads not just slick but sticky. If it’s hot, they head out by 7 a.m., driving as far as they can by road, and start hiking, either to one of Wilson Mantilla’s sites or just exploring.

Judith Wake said she and Bruce have written agreements with some private ranchers to dig, collect and restore the fossils, and use them for education. Some others, however, are “very negative about ‘bone diggers’ — they might turn you in if you cross one foot onto their property.” Still others, she said, hoard what they think of as buried treasure, not realizing it is decaying away with the efforts of plant roots, insects and the freeze-thaw cycles shifting the ground.

Carrying hammers, pickaxes, brushes and water, their packs weigh 15-20 pounds before they find anything, and they often hike 4 or 5 miles.

“It can be disappointing — sometimes you think you’ve got something great, you get about 6 inches in, and you’re done,” Judith Wake said.

Even worse is coming across a poached site — with the most valuable pieces, like skulls or teeth, taken, and the rest abandoned or scattered. “They cherry-pick what they can sell,” she said.

Judith said the love of discovery and being outdoors in the high plains desert keeps the Wakes coming back: “It’s just the excitement of, ‘What are we going to find today?’”


Finding her first fossil

Isobel Ruiz got more than a taste of that excitement. A UW mechanical engineering major, she got hooked on paleontology after her first class and began volunteering with Wilson Mantilla. She found her first fossil — part of the triceratops — on this summer’s dig.

The triceratops’ frill — the formation on the back of its head that looks like Shakespeare-style neckwear — was spotted in 2019, emerging from a butte by a rancher flying over to check his cattle, earning it the nickname “Flyby Trike.” The rancher notified Wilson Mantilla, who had the Wakes verify the find. Wilson Mantilla and the collective group excavated the frill — and then COVID-19 stalled the excavation.

So most of Flyby Trike was waiting for the team this summer. The job of Ruiz and her teammates was to see which — if any — viable bones remained.

The excavation process is to dig a big trench, leaving ample room around the fossil — while checking for more bone, seeking the limits of the site. Once you have gone 1 meter to the right and left without finding bone, you can start making a plaster jacket to transport the specimen.

“I found the first [significant] piece of bone beside the previously discovered skull,” Ruiz said. “Just that moment of finding my first fossil and feeling the gravity and importance of that discovery — it was amazing!”

Burke paleontologists believe Flyby Trike was likely an elder, based on the fusing of the bones along the frill, and one of the last of its kind alive before the extinction. Flyby was found alongside fossilized amber and seedpods from that period — giving paleobotanists a lens into the wider ecosystem. It would have been an eventful dig for anyone — but there were more surprises ahead for Ruiz.


“At the hadrosaur site, we were digging under what we had already plastered and taken away when another volunteer and I ended up finding a rib,” she said. “Just seeing this rib and how long it took to start curving made us realize it must have been as big as a city bus.”

And then they saw the vertebra. 

“It was wider than my hand — I’ve never seen a vertebra that big,” Ruiz said.

Finding Chewie

Dave Fuqua, a teacher from Glendive, Montana, regularly scouts for fossils in the area and showed Wilson Mantilla some promising sites in 2019 that were excavated this summer, turning up several fossils, including the claws, vertebrae, ribs and scapula of a specimen the team called “Chewie” after Fuqua’s nickname. It’s a cute name for this possible Anzu — a beaked, crested, ostrich-sized dinosaur with serious claws. 

Further finds this month added hips and toes to the puzzle. After being surrounded by protective plaster field jackets, specimens were taken to the Burke Museum’s prep lab. 

Chewie needs time to be evaluated for the type and species to be confirmed, Wilson Mantilla said.

The larger mission

Wilson Mantilla’s mission with the Hell Creek Project is bigger than dinosaurs. His team is looking at adaptive shifts in ecosystems in response to drastic temperature change — which may indicate Earth’s species were greatly weakened before the deadly asteroid that hit 66 million years ago and wiped out the dinosaurs.


Hell Creek Formation samples indicate that, starting about 300,000 years before the asteroid event, there were drastic temperature swings — at the same time, the Indian subcontinent experienced strong amounts of volcanic activity, spewing massive amounts of noxious gases and lava. “We think that may be the one-two punch that made the asteroid do them in,” said Wilson Mantilla.

The changes that took place in the Cretaceous left communities more vulnerable to disaster — in this case, an asteroid,” he said. “It destabilized the ecosystem in the Cretaceous. Those sorts of changes may well translate to the ones we are having today.”

Wilson Mantilla says the question is: What are the characteristics of food webs that are the most stable in the face of change, and how do they recover? Learning about resiliency in times of climatic stress could be useful to humans right now.

“Our broader goal,” he said, “is to be able to take this particular case study of the Cretaceous and learn about the fragility of ecosystems and their ability to recover.”