Most Coloradans harbor a fond appreciation for the state’s mountain ranges and beautiful landscapes, but it can be awe-inspiring to recognize the area once supported a larger abundance of dinosaurs than anywhere else in the continental U.S.
Even more incredible is that the fossils of these remarkable creatures are often right beneath the homes, offices, stores, parks, and concert venues we go to.
“What’s amazing about Colorado and the Denver metro area is we’re centrally located in the best dinosaur ecosystem of anywhere in the world,” said Dr. Joe Sertich, Dinosaur Curator at the Denver Museum of Nature and Science.
“Other places don’t have major metropolitan areas sitting on top of dinosaur beds,” said Sertich. “But here in Denver we live right on top of the fossils.”
Sertich has studied dinosaur fossils around the world, including in Africa and Antarctica. Ten years ago he returned to his hometown of Denver to research fossils in the Colorado area.
Colorado was at the Center of the Bone Wars
At many points in its history, Colorado had a higher volume and greater concentration of dinosaurs than anywhere in the country.
“It was often a five-car race between these western states for who has the most rich and abundant dinosaur presence, with the lead switching between Colorado, Utah, Wyoming, Montana, and New Mexico,” explains Sertich. “Colorado at various points in history has been the top dinosaur state.”
At one of these points, during 1887, the discovery of fossils on the Morrison Formation generated excitement throughout the paleontology community. Named after the town of Morrison, CO, where it was discovered, the formation was ultimately found to stretch through most of Colorado and into nearby states.
The formation was at the center of “bone wars” during the late 19th and early 20th centuries. At that time, scientists from all over the country rushed to our foothills on fossil survey expeditions. Top paleontology teams of the time engaged in a ferocious competition to make the greatest discoveries.
“There were a lot of notable finds and important ‘firsts’ from that era, including the first Talasaurus, Rajasaurus, and Apatosaurus,” said Sertich.
The abundance of fossils and resources here is one of the reasons why Sertich relocated. “We have one of the most active dinosaur research programs anywhere in the United States, right here at the Denver Museum,” he said. The museum’s scientific research and public education efforts take museum patrons through some of Colorado’s oldest natural history. Here’s some of what museum-goers learn:
Paleozoic Era (500M to 250M years ago)
Get up close: Front Range, Flatirons, I-70 Corridor
The soil on many of the rock layers that we see in Colorado today was deposited around the time of the Paleozoic era about 300-350 million years ago. Rivers deposited the bedrock layer that is known as the Fountain Formation which is still visible in many areas of the Front Range, including Red Rocks Amphitheater, the Boulder Flatirons, and Vail Mountain scenery.
“The mountains that we see today along I-70 are the basement rocks,” explains Sertich, “It’s much older rock from the Precambrian and Cambrian eras. Those were really deep in the earth when the seaway was covering us, and it wasn’t until about 70 million years ago when all of that rock began to push up.”
About 280 million years ago another layer of rocks, known as The Lyons Formation, contributed to the sandstone soil that we see in other areas of Colorado. This is easy to see at the Garden of the Gods in Colorado Springs and Roxborough State Park in Littleton.
Jurassic Period (201M to 145M Years Ago)
Get up close: Morrison, Delta, LaJunta, Trinidad
“Many dinosaur fossils from the Jurassic period came from the Morrison Formation,” Sertich explains. Many significant species dwelled in Colorado and were discovered on the Morrison Formation. The Stegosaurus that was found during the bone wars was an especially remarkable dinosaur with highly distinctive characteristics, such as armored spikes lining its spine and tail. As a result, the Stegosaurus eventually became our official state dinosaur.
The Barosaurus was another exciting dinosaur near Morrison during the Jurassic era. It had an extensive frame stretching seventy-five feet long, a high neck rising forty feet high, and a massive body weighing over thirty tons.
The Dry Mesa Quarry is another part of the Morrison Foundation that helped the state earn a reputation as a prominent fossil hub. Located near Delta, Brigham Young University researchers led by James Jensen explored the quarry in 1972 and immediately discovered the Supersaurus. With a body reaching 110 feet in length, this was the longest dinosaur ever found in North America at the time.
Many other massive dinosaurs from the Jurassic period were found on the quarry, including the Seismosaurus, Torvosaurus, and Brachiosaurus.
With just a short drive from Denver or Boulder, enormous dinosaur footprints can be seen today at Dinosaur Ridge in Morrison. The park was established in 1989 to commemorate the natural history of the Morrison Formation and to showcase the dinosaur fossils preserved in the area. The park features long trails that are revered for having among the best dinosaur footprint tracks in the world.
Not to be outdone, a longer drive to Dinosaur Lake near La Junta will reveal about 1,500 footprints representing over 100 dinosaur species. Still more tracks can be found at Trinidad Lake in southeast Colorado.
The Cretaceous Period (145M Years ago)
Get up close: your own backyard, Snowmass, Greeley, Littleton, Highlands Ranch, Thornton
The Cretaceous period began around 145 million years ago and comprised the final years of the dinosaur period. For a time in Colorado, inevitable circumstances caused a gap in which the state did not harbor any dinosaur life. Then, suddenly, the region experienced a prolific explosion of dinosaur life at the end of the period.
“The Western Interior Seaway was covering most of the central part of North America, and about 90 million years ago most of Colorado was also covered,” explains Sertich, who specializes in the Cretaceous period.
“But we have amazing records of the life that lived at the same time as the dinosaurs but in a marine setting, like Amanites, which are big coiled or straight-shelled squid-like ancestors; and marine reptiles that fed on Amanites, like Mosasaurs and Plesiosaurs. We have a record of these fossils here in Colorado even as high up in the mountains as Snowmass, where we have a giant fish that was found in the 1960s from the Seaway.”
Many fossils from the Seaway era can also be found in the Denver area and the Front Range.
“It’s not uncommon for people in the Denver metro area to find bits of bone and teeth in their own backyard, especially from those Amanites,” continues Sertich.
The Cretaceous Period (70M Years ago)
Get up close: Greeley, Littleton, Highlands Ranch, Thornton
70 million years ago the water from the Seaway gradually receded, dry land became increasingly available, and the dinosaurs promptly inhabited the land that opened up. This is also when our Rocky Mountains rose from the ground and began to assume its current shape.
The Denver Formation is a prominent deposit of bone-infused land established during the late Cretaceous period; a wide variety of remarkable dinosaurs dwelled on this newly formed land.
“During the Cretaceous period we have the appearance of the horn dinosaurs related to Triceratops, the duck-billed dinosaurs known as Hadrosaurs, and then we had the Tyrannosaurs here as well,” explains Sertich. “The evolution of the Tyrannosaurs goes back to about 85 million years ago, and then we ended up with the largest Tyrannosaurs, with the T-Rex, at the very end of the Cretaceous period.”
Many fossils of dinosaurs from the late Cretaceous period are still being discovered in the Denver metro area. In 1982, a Triceratops that was found in Weld County was named “Pops” and became the official county dinosaur.
“The great thing about this Pops project and having the museum study the fossil is that it provides an opportunity for our residents to learn more about where they live,” says Jennifer Finch, Weld County Public Information Officer. “It’s fun to see discoveries from far-away places, but it’s a bit different when you know something amazing like a dinosaur fossil was found near the very place you live or pass by frequently.”
Pops is on display in the lab window of Prehistoric Journey at the Denver Museum, where Sertich and his team are working with the specimen.
Another find occurred in 1992 when a T-Rex that was buried in Littleton was discovered by a construction crew performing work on an apartment complex. The next year, a Triceratops that was found while crews were building Coors Field encouraged the Rockies to establish a purple dinosaur with horns as the team’s mascot.
More recently, in 2017, a dinosaur that was found in Thornton while a construction crew was building a new police station and firehouse turned out to be a Torosaurus. Then again, in 2019, a comprehensive Triceratops skeleton was found in Highlands Ranch just beside Chatfield Reservoir.
Dr. Sertich and his team are currently examining the fossils from the Triceratops and preparing to remove the bones from the site. “We’re still prepping and cleaning them,” Sertich said. “But it looks like there are multiple dinosaurs at the site around Chatfield Reservoir, including the most complete Triceratops ever found in Colorado. It includes most of the skull and big parts of the skeleton from the hips, tails, arms, and legs. It’s also a large Triceratops specimen, so that’s a really cool local find that happened in the last couple years.”
Although the Denver metro area was a busy time for dinosaurs during the late Cretaceous period, eventually the asteroid that slammed into the earth facilitated the mass extinction of land dinosaurs. The asteroid is believed to have struck in Mexico around 65 million years ago, but people can actually see residue from the cataclysmic event right here in southern Colorado.
Located in Trinidad Lake State Park, the Colorado K-T boundary is a large rock coated with ash chemicals that were deposited when the asteroid struck the earth, dust filled the sky, and the dinosaurs went extinct.
Cenozoic Era (65M Years ago to the Modern Day)
While the asteroid event was unfortunate for dinosaurs, the impact of the asteroid and the extinction of the dinosaurs was necessary for the evolution of humans. During the Cretaceous period, our early ancestors were small, foraging mammals. It seems highly unlikely that our ancestors could have coexisted for long with ruthless dinosaur predators.
We also appreciate the great work that the paleontology community has done to tell us the compelling history of our planet, our region, and our state. Their ability to extract fossils from the ground, ascertain information from these old bones, and convey the details of their discoveries empowers all of our minds with an enhanced understanding regarding how the world existed and how it came to exist today.