On a bare rock plateau in central Bolivia, the ground looks like it has been stamped again and again by three-toed shoes. A new study has counted 16,600 fossil dinosaur footprints there, turning the Carreras Pampa site in Torotoro National Park into the largest dinosaur tracksite yet described.
Led by paleontologist Raúl Esperante of the Geoscience Research Institute (GRI) in California, an international team mapped not only walking tracks but also swim marks and tail drags left more than 60 million years ago along an ancient shoreline. Their work suggests that this part of the Andes once worked like a busy coastal road for meat-eating dinosaurs, offering a rare view of how these animals moved through their environment near the end of the Cretaceous period.
A fossil traffic zone in the Bolivian highlands
Carreras Pampa lies inside Torotoro National Park, a semi-arid landscape of canyons and plateaus in the Bolivian Andes. Over about 7,500 square meters of exposed rock, the team documented 1,321 trackways, which are lines of prints left by the same animal, and 289 isolated prints, totaling 16,600 three-toed theropod footprints.
The tracks range from tiny marks less than 4 inches long to prints more than 12 inches across, hinting at both small dinosaur species and juveniles of larger predators. All belong to theropods, the mostly two-legged carnivorous dinosaurs that include famous names such as Tyrannosaurus rex, though the exact species that walked here remain unknown.
In some sectors, the rock is so covered in overlapping footprints that it resembles a crowded sidewalk after a rainstorm. The study concludes that Carreras Pampa now holds world records for the number of individual dinosaur footprints, continuous trackways, swim trails and tail marks preserved in one place.
Tracks that show walking, running and swimming
Dinosaur footprints are valuable to scientists because they record movement, not just bones. At Carreras Pampa, the team identified many kinds of walking tracks and swim tracks, based on shape, depth and how the mud was pushed aside.
Swim tracks appear as long, shallow scratches where a dinosaur in chest-deep water pushed forward by scraping the lake bottom with its clawed toes. In other places, winding grooves connect several footprints, showing that some animals lowered their tails and dragged them as they walked on soft ground.
By measuring stride length and foot size, researchers estimated the animals’ speeds and body sizes and found that almost all of them were moving at a walking pace, with only about 1 percent of tracks recording running. Read in sequence, some trackways show sudden turns or uneven steps that might reflect a limping animal or one reacting to an obstacle, a bit like following someone across a muddy soccer field and seeing where they slowed down or changed direction.
Reconstructing a lost shoreline
One of the most striking patterns is direction. Most trackways line up northwest to southeast, the same orientation as ripple marks in the rock surface, which are small frozen waves in the ancient mud. This suggests that the dinosaurs were walking along the edge of a shallow body of water such as a tidal flat or lagoon rather than wandering randomly across open land.
Geological clues from the sediments and from tiny burrows made by shellfish-like animals indicate that the mud was wet and soft when the animals passed by, then flooded and covered with fresh layers of sand and silt. Over time those layers hardened into rock and were later stripped by erosion, exposing the track-bearing surface so visitors today can stand where the shoreline once was and literally walk between the footprints.
Why this dinosaur highway matters
Large dinosaur tracksites are known from places such as Lark Quarry in Australia and Dinosaur Valley State Park in Texas, where a few thousand footprints record dramatic scenes like river crossings. Carreras Pampa eclipses those sites with its sheer number of tracks, the length of its swim trails and the abundance of tail marks, building on earlier research that had already highlighted Bolivia as one of the countries with the richest dinosaur footprint record.
Researchers still debate why so many animals funneled through this one place, whether it was a seasonal migration route, an everyday path between feeding and resting areas, or a safer strip of firm ground along the waterline. Photogrammetry, a technique that uses many overlapping photos to build 3D models, suggests that thousands of additional footprints remain to be mapped across Carreras Pampa, even as farming, road building and erosion continue to threaten some parts of Bolivia’s fossil record, and the rocky “dinosaur highway” is drawing visitors, supporting local guides and giving scientists fresh material to study.
The main study has been published in PLOS ONE.
