A heavily trafficked “dinosaur highway” may once have crossed the coastline of what is now Bolivia. Theropods, three-toed, bipedal, carnivorous dinosaurs, traveled along this busy route, leaving behind thousands of fossil tracks. Paleontologists have described their tracks for the first time, providing a rare glimpse into the dinosaurs' movements through their habitat.
Scientists recently counted 16,600 theropod tracks—more than any other trail site—on the Carreras Pampas Trail in Torotoro National Park in Bolivia. There, theropods trampled soft, deep mud with their feet between 101 and 66 million years ago, near the end of the Cretaceous period.
The study is the first scientific study of the footprint areas, which extend over approximately 80,570 square feet (7,485 square meters). Some tracks were isolated, but many formed tracks or multiple prints made by the same animal, the researchers reported Wednesday in the journal. PLOS One.
“Everywhere you look at this layer of rock at this site, you will see dinosaur footprints,” said study co-author Dr. Jeremy McLarty, assistant professor of biology and director of the Dinosaur Science Museum and Research Center at Southwestern Adventist University in Texas.
Most tracks went north-northwest or southeast, McLarty told CNN. They were likely created in a relatively short period of time, indicating that the area was a popular highway for theropods and may have been part of a larger dinosaur highway that spans Argentina, Bolivia, and Peru.
The shapes of the prints and the distance between the tracks showed how the animals moved; some walked leisurely while others ran along the muddy shoreline, and more than 1,300 tracks showed evidence of shallow water swimming, the researchers said.
Several of the tracks bore marks from theropod tails, and the varying lengths and widths of the tracks suggested that the dinosaurs varied greatly in size, from hip heights of about 26 inches (65 centimeters) to more than 49 inches (125 centimeters). Several hundred additional tracks at the site were left by birds that shared the shoreline with dinosaurs.
“Incredible Consequences”
The footprints are preserved in what used to be soft, deep mud. Yarn lines help researchers mark which tracks belong to each track. – Raul Esperante
Identifying thousands of individual prints and describing different gaits “has incredible implications for reconstructing these ancient habitats and how dinosaurs and birds used them,” said paleontologist Sally Hurst, who was not involved in the new study. Hirst is an adjunct research fellow in the School of Life Sciences at Macquarie University in Australia.
The tracks are preserved at varying depths in what was once soft, deep mud, “which can often end up recording a lot about how these animals moved their legs,” Dr. Peter Fulkingham, a professor of paleobiology at Liverpool John Moores University in the UK, told CNN via email.
“I'm interested in the deeper tracks that preserve most of the movement of the foot, and they have fairly long tracks,” said Falkingham, who studies dinosaur tracks but was not involved in the new study.
For example, swimming lanes are “very different from regular walking paths,” McLarty said. When the theropod rose to floating water, its middle toe sank deeper into the mud, while the other two toes and heel left behind a much lighter impression.
“Tracks are records of the soft tissues, movements and environments that dinosaurs actually lived in,” Falkingham added. The site, with its many tracks of animals of different sizes moving in different ways, “really brings these lost ecosystems to life in a way that bones don't.”
Leaving an impression
Places like Carreras Pampas show how dinosaurs moved. More than 16,000 theropod tracks have been found here. – Raul Esperante
Since the 1980s, Carreras Pampas has been known for its dinosaur footprints, but their scale and number have never been studied in detail, McLarty said. His team's work raises new questions about this preserved fragment of South American Cretaceous life, such as why almost all of the tracks are theropods and why there are so many of them, McLarty said.
Numerous remains of sauropods, the long-necked plant-eating dinosaurs that grew larger than any living land animal, remain in many places around the world. Sauropods, like many species of large modern herbivores, are known to have traveled in herds. In comparison, theropods are carnivores that do not typically roam in large groups.
Bolivia is known for its numerous pathways dating back to the Triassic, Jurassic and Cretaceous periods, the study authors report. Before the mapping of the Carreras Pampas, the site with the most dinosaur tracks in the world was also in Bolivia: Cal Orco in Sucre, dating to about 68 million years ago and containing about 14,000 prints.
“How is what we find in Carreras Pampas related to other sites in Bolivia?” asked McLarty. “What big picture emerges when we start comparing different sites?”
These thousands of tracks provide important clues about dinosaurs that fossil skeletons cannot, because the tracks show how living animals moved, said paleontologist Dr. Anthony Romilio, a postdoctoral fellow at the University of Queensland in Australia, who was not involved in the study.
“The skeleton shows what the animal could do; the tracks show what it actually did, moment by moment,” Romilio told CNN via email. “They record speed, direction, turns, sliding, posture, and sometimes group movement.”
The Carreras Pampas tracks are significant because of the different size theropods represented there, Romilio said. “This may reflect multiple species, multiple age classes, or a combination of both.”
And unlike fossilized bodies, footprints preserve the dinosaur's connection to a specific place when it was alive. Bones can be transported after the animal dies, “so where you find a dinosaur bone may not be where it was,” McLarty noted. By comparison, the trails provide a direct snapshot of an ancient moment in time—in this case, when scores of scurrying theropods crossed the coastline.
“The tracks are not moving,” McLarty said. “When you visit Carreras Pampas, you know you are where the dinosaur walked.”
Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American, and How It Works. She is the author of “Rise of the Zombie Bugs: The Surprising Science of Parasitic Mind Control” (Hopkins Press).
Register for CNN Science Newsletter Wonder Theory. Explore the universe with news about exciting discoveries, scientific advances, and more.
For more CNN news and newsletters, create an account at CNN.com
