Twenty miles east of Fort Stockton, 7 miles north of I-10 on Highway 67, a rest area beckons the road-weary traveler. From covered picnic tables here, a short trail leads to a metal structure, a cage above exposed limestone bedrock. Look closely at that bedrock, and you’ll see impressions of a “tridactyl” or three-toed shape. These are the footprints of a theropod dinosaur, part of a lineage that includes T-Rex, and all living birds.
The Pecos County dinosaur prints are the most prominent in our region. But there are more than 50 such sites in Texas, from the Hill Country north to Fort Worth, and Dinosaur Valley State Park. These trackways are a fossil record unlike any other, and they tell an awe-inspiring, if haunting, story.
Dr. Thomas Adams is a paleontologist at San Antonio’s Witte Museum.
“As I talk to kids, I'm always like, ‘Bones are the remains of dead things; teeth, shells – they're all remains,’” he said. “‘Something has to die in order to get those fossils. Footprints are evidence of animals that were alive. This animal walked here, and he was living when he left.’”
Dinosaur footprints are Adams’s speciality. With National Science Foundation funding, he and his collaborators have used drones, 3D imaging and other techniques to analyze the trackways.
There are consistent themes, Adams said. Three types of dinosaurs are represented in the Texas prints – predatory theropods; herbivorous ornithopods; and sauropods, the group of long-necked dinosaurs that included Brontosaurus. All the tracks were made by very large creatures. And all are found in limestone rocks called the Glen Rose Formation, which dates to between 115 and 105 million years ago.
At that time, in the Early Cretaceous Period, ocean waters from the ancestral Gulf of Mexico were beginning to inundate Texas. Those seawaters would eventually cut North America in half.
The conditions along the shoreline were ideal for preserving footprints. These tidal flats were of a lime-rich mud – which quickly took on the consistency of concrete in the baking sun. Footprints on a sandy beach obviously don’t last. But these did, to be exposed eons later across Texas.
They’re glimpses of fleeting moments in the Dinosaur Age, Adams said.
“Geologically speaking, we're used to talking about millions of years,” he said. “But there are places where I can talk about, ‘Oh, this was a day or two days or a week at the most.’ So we really are looking at individual snapshots of dinosaurs moving through a space.”
Some of the prints may be of Sauroposeidon; with a head that reached 60 feet high, it was the tallest dinosaur ever. The theropod prints include those of Acrocanthosaurus – after T-Rex, the continent’s second largest carnivore. Some of the dinosaurs walked alone; others moved in groups.
The absence of smaller dinosaur prints is striking. Through detailed rock analysis, Adams’s team has learned what this shoreline environment was like. It was brutally hot, and incredibly harsh. Perhaps smaller dinosaurs couldn’t survive it. But for immense reptiles, the open shoreline may have been a kind of highway.
Big animals need big ranges — perhaps these dinosaurs were dispersing in search of new resources?
“There's no food, there's no fresh water,” Adams said, “but yet these dinosaurs are walking across these exposed shorelines. It's amazing stuff. What are they doing? Where are they going? That's one of those things we probably will never know.”
In addition to the Pecos County example, there are footprints on the UTEP campus in El Paso. And there are reports of dinosaur footprints along the Rio Grande in Mexico, just opposite Big Bend National Park.
If you see these footprints, remember: Vanished titans passed this way.
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