A massive trove of fossil footprints in central Bolivia reveals how dinosaurs lived, moved, and interacted with their world.
Long held legends claimed that the enormous three-toed marks scattered across the Bolivian central highlands belonged to supernatural monsters with claws strong enough to bite into solid rock. In the 1960s, scientists debunked these fears, showing that the prints were left by gigantic two-legged dinosaurs stomping through ancient waterways in what is now Toro Toro, a village that sits beside a famous national park in the Bolivian Andes.
In a groundbreaking effort, a team largely comprising paleontologists from California’s Loma Linda University has documented 16,600 theropod footprints—the dinosaur group that includes Tyrannosaurus rex. The researchers spent six years conducting regular fieldwork, and their findings, published in the journal PLOS ONE, represent the largest collection of theropod footprints ever recorded.
There’s no other site in the world with such an abundance of theropod tracks, noted Roberto Biaggi, a co-author of the study led by Spanish paleontologist Raúl Esperante. The team proudly points to Toro Toro as holding multiple world records for footprint discoveries.
The footprints offer a window into dinosaur behavior, including evidence that some individuals attempted to swim. The footprints indicate that the animals pressed their claws into soft, muddy lakebottom sediment just before water levels rose, then the rising water preserved the tracks for posterity.
Experts not involved with the study praised the preservation quality. Richard Butler, a paleontologist at the University of Birmingham, commented that the number of footprints and trackways at Toro Toro is unprecedented and provides a remarkable glimpse into the lives of dinosaurs at the very end of the Cretaceous period, around 66 million years ago, just before an asteroid impact that led to mass extinctions.
Despite their age, these traces have faced ongoing threats. For decades, agricultural activity—such as threshing corn and wheat—has disturbed the plateaus covered in tracks. Quarries nearby blasted rock for limestone, and more recently, highway work nearly erased a major tracksite before intervention by the national park.
The site’s many traces contrast with its scarce fossil bones. While footprints and swim traces are plentiful, skeletal remains are rare compared with better-known regions like Argentine Patagonia and Brazil’s Campos.
This lack of bones might reflect natural factors as well. The researchers argue that the patterns and concentration of tracks, all within the same sediment layer, suggest that dinosaurs were traveling along an ancient coastal superhighway stretching from southern Peru into northwest Argentina, rather than lingering in one place.
The size range among footprints implies a diverse herd: some giants standing about 10 meters tall moved alongside much smaller theropods, roughly the size of a chicken, with hips about 32 centimeters tall.
Footprints can reveal behavior that bones cannot, said Anthony Romilio, a paleontologist at the University of Queensland who did not participate in the study. They show whether dinosaurs were strolling, sprinting, pausing, or turning, offering daily-life insights beyond what skeletons alone can provide.
Why so many dinosaurs congregated at this windy plateau remains a mystery. Romilio suggested they might have frequented a vast ancient freshwater lake and its expansive muddy shoreline. Biaggi offered the possibility that the herd was fleeing a threat or searching for a settlement site.
Either way, the Toro Toro tracksite promises to keep yielding discoveries. Biaggi believes the work will continue for years, with many more footprints found at the fringes of already uncovered areas.
