A dinosaur died on Animas City Mountain in Durango about 150 million years ago, and in December of 2021, a local fossil hunter found its bones.
Tom Eskew, a certified arborist and amateur fossil hunter, said he had walked over them hundreds of times until one day, he looked down and realized there were fossils in his path.
“The most valuable finds in paleontology are actually made by amateurs who then report them,” said Dr. Jon Powell, an adjunct at Fort Lewis College who specializes in geobiology. “There are a lot more people wandering around the hills and looking at stuff than we could ever accomplish ourselves.”
Eskew said he initially thought they were sea life fossils because that was all he had previously found in Durango.
He called John Gleason, a senior lecturer of the geosciences department at FLC, to come look at the fossils, Eskew said.
“It sure looked like dinosaur bones to me,” Gleason said. “They were only about four or five inches long so I thought they were finger bones or phalanges of some large dinosaur.”
He contacted his colleague, Jon Powell, who saw them and initially thought that they were femur bones of a baby dinosaur, Gleason said.
“Whether they really belong to some kind of baby dinosaur, or whether they’re just a small dinosaur or just some broken up pieces of other bones is really difficult to tell because of the wear and tear of where these things are,” Powell said.
He said the bones looked to have had their articulate ends missing, the ends of bones that grow on their own and are connected by cartilage to the middle bone.
“It could be because someone gnawed on you,” Powell said. “It could also be because when a baby is hatched out and starts growing, it hasn’t developed these articulate ends yet, but unless you find it crawling out of an egg, it’s going to be pretty hard to identify.”
Powell said that it isn’t very common to find a skeleton that is buried intact and can be identified immediately.
“We have certain shapes of dinosaurs and they have definite characteristics, but trying to take a leg bone and then pinpoint exactly which species that leg bone belonged to might be pretty difficult,” Powell said.
The fossils lie in a sedimentary rock that is very compact.
“The more that I’ve been thinking about it, the more I realize that this is probably not something that can be easily collected and taken out of that area,” Powell said. “So I think it’s going to be one of those cases where people continue to walk by these fossils and every once in a while someone will notice what they are.”
Eskew said that when looking for fossils, plant fossils tend to look more like an image of the plant, whereas animal fossils are more black and carved out.
The formation where the dinosaur bones were found is called the Morrison Formation, Powell said.
The Morrison Formation spans from Montana, through Wyoming, into Colorado, across Utah and into New Mexico.
This was the first dinosaur bone Gleason had seen in the Morrison Formation in Durango, he said.
It formed in the Upper Jurassic period when there were a lot of dinosaurs, which is why people find many dinosaur fossils in it today, Gleason said.
It’s a gray-green, sedimentary rock that is a combination of limestone, shale and sandstone, and was deposited in a shallow lacustrine environment or a lake and river environment over time, he said.
When there were dry periods, groups of herbivorous dinosaurs would migrate north or south in order to have a continual supply of food, since seaways were constricting North America at the time, Powell said.
“When dinosaurs are walking along and get into certain areas, when they’re crossing arroyos and stuff like that that may have existed back then, every once in a while one would get caught in a flash flood or trapped in quicksand,” Powell said.
After a while, there would be layer upon layer of these dinosaur skeletons stacked up in this kind of situation, he said.
150 million years ago, the climate would’ve been a lot wetter and a lot warmer which was a good, lush environment for dinosaurs to live in, Gleason said.
It was also a good environment for fauna that no longer exists in this area, such as ferns and palms, Powell said.
Eskew said that he and his sons have found many petrified plants in the Morrison Formation since they’ve started looking.
“The reason we have a different environment now than in the Jurassic is because of plate tectonics,” Gleason said. “The plates have been shifting over time and our area where we are today was closer to the equator, it was a warmer environment.”
Since then, there has been almost 150 million years of deposition and volcanism that formed thousands of feet of rock that can be seen in Durango’s layered landscape today, Gleason said.
“It’s an amazing landscape that has changed vastly since the time of the dinosaurs,” he said. “It’s changed remarkably from being completely under water, to moving a little bit further north than it is today. It’s a colder and drier environment than it used to be.”
Right now this climate couldn’t support a dinosaur, which shows the fossil evidence of a changing environment over time, Gleason said.
By the time this climate and landscape can support dinosaurs again, humans will most likely be extinct because very few land animals have a 100 million year lifespan, he said.
These dinosaur fossils “put your place in time in perspective, which is very insignificant,” Eskew said.
Gleason said that he likes the fact that the dinosaur bones are in a place that people can walk over and only notice if they’re paying close attention.
“They’ve been there for so long, they’re not going to get taken, they’re not going to get eroded away,” he said. “I think they should stay there.”
Eskew said he could go both ways on wanting these dinosaur bones to be taken out and protected versus keeping them where they are.
“It would be kind of cool for people to be able to see it if it is a rare find, but then again it’s cool to just touch it when we walk by and think about the animals' history,” he said.
Powell said that it can be difficult to get fossils out of the Morrison Formation since it is so compact, but he got excited when he saw these dinosaur fossils in Durango.
“I don’t think I will ever get tired of going out and taking a look at rocks and all of a sudden seeing something really cool,” he said.