16,600 Theropod Footprints Found in Toro Toro, Bolivia — World's Largest Dinosaur Tracksite Reveals Behavior

Toro Toro, Bolivia — For generations local legend explained the huge three‑toed depressions pockmarking the central Bolivian highlands as the work of supernatural beasts. Scientific visitors in the 1960s showed the impressions were instead the tracks of gigantic, two‑legged theropod dinosaurs that walked the shallow waterways of present‑day Toro Toro more than 60 million years ago.

Over the past six years, a team of paleontologists — largely from California’s Loma Linda University and led by Spanish researcher Raúl Esperante — systematically surveyed and cataloged tracks across the site. Their paper, published in PLOS One, documents 16,600 theropod footprints and an additional 1,378 traces interpreted as swim or scratch marks. The authors report this is the largest single concentration of theropod footprints yet recorded anywhere in the world.

“There’s no place in the world where you have such a big abundance of (theropod) footprints,”

— Roberto Biaggi, co‑author of the study.

Prints Record Dinosaur Behavior — Including Attempts To Swim

The preserved impressions offer a rare behavioral snapshot. Many scratches and partial prints appear to show theropods pawing or scrambling in soft lake‑bottom sediment as water levels rose and sealed their tracks, protecting them from subsequent erosion. From track spacing and depth, researchers can tell when animals walked slowly, sped up, stopped or changed course.

Richard Butler of the University of Birmingham, who was not involved in the study, praised the quality of preservation:

“The preservation of many of the tracks is excellent,”

and added that the sheer number of footprints and trackways at Toro Toro is unprecedented.

Footprint Sizes, Dating And What They Reveal

Tracks in the same sedimentary layer indicate these footprints date to the end of the Cretaceous period (roughly 60–66 million years ago). The range of sizes recorded — from giant theropods estimated at about 10 meters (33 feet) tall to tiny relatives about 32 centimeters (1 foot) tall at the hip — suggests groups containing both enormous and chicken‑sized individuals moved through the area together.

Preservation Threats And The Mystery Of Missing Bones

Despite surviving for tens of millions of years, the tracks have been endangered by modern human activity. Farmers have traditionally threshed crops on footprint‑covered plateaus, quarry workers blasted limestone layers, and, until the national park intervened, highway crews nearly destroyed a major concentration of tracks during tunneling operations.

These disturbances may partly explain why the region yields very few bones, teeth or eggs compared with fossil‑rich regions such as Argentine Patagonia and some parts of Brazil. The research team also suggests a natural explanation: the concentration and alignment of tracks across a single layer imply many dinosaurs were moving along an ancient coastal corridor that stretched from southern Peru into northwest Argentina, rather than settling permanently at Toro Toro.

Why So Many Dinosaurs? Ongoing Research

The reason large numbers of theropods congregated here remains unclear. Some scientists suggest repeated visits to a broad freshwater shoreline; others propose they could have been fleeing a threat or searching for new habitat. Whatever the cause, Toro Toro’s record provides unique behavioral insight that skeletons alone cannot convey.

“I suspect that this will keep going over the years and many more footprints will be found right there at the edges of what’s already uncovered,” said Biaggi. Continued fieldwork and protective measures by the national park will be critical to preserve and expand knowledge of this exceptional site.