For generations, local legend in the central highlands of Bolivia spoke of colossal, three-toed footprints believed to be the work of supernatural beasts, creatures so powerful they could embed their claws into solid rock. These tales spurred both fear and awe, painting a picture of mythical monsters roaming the Andes.

However, the mystery of these ancient tracks was unraveled in the 1960s when scientists arrived in the region. They dispelled the myths, revealing that these peculiar footprints were actually the remnants of enormous, bipedal dinosaurs. These prehistoric giants had once trampled and splashed through the waterways of what is now Toro Toro, a quaint village nestled within a popular national park in Bolivia.

In recent times, a dedicated group of paleontologists, primarily from California’s Loma Linda University, made a groundbreaking discovery. Over six years, they meticulously cataloged 16,600 footprints left by theropods, the dinosaur lineage that includes the formidable Tyrannosaurus rex. This extensive study, published in the peer-reviewed journal PLOS One, highlights that this location boasts the world’s largest collection of theropod footprints ever recorded.

“There’s no place in the world with such an abundance of theropod footprints,” stated Roberto Biaggi, a co-author of the study spearheaded by Spanish paleontologist Raúl Esperante. “We have all these world records at this particular site,” he added, emphasizing the significance of their findings.

Prints record dinosaur behavior — including attempts to swim

The study also sheds light on the behavior of these ancient creatures, suggesting that these dinosaurs not only dominated the land but also made clumsy attempts to swim. Their efforts left behind 1,378 additional traces, etched into what was once the soft sediment of a lake bottom, narrating a story of a bygone era when these giants roamed freely.

They pressed their claws into the mud just before water levels rose and sealed their tracks, protecting them from centuries of erosion, scientists said.

“The preservation of many of the tracks is excellent,” said Richard Butler, a paleontologist at the University of Birmingham who was not involved in the research. He said that, to his knowledge, the number of footprints and trackways found in Toro Toro had no precedent.

“This is a remarkable window into the lives and behaviors of dinosaurs at the end of the Cretaceous,” Butler added, referring to the period around 66 million years ago at the end of which an asteroid impact abruptly extinguished all dinosaurs and 75% of living species along with them, according to scientists.

Footprints face preservation threats

Although they’ve survived for millions of years, human life has threatened these traces. For decades, farmers threshed corn and wheat on the footprint-covered plateaus. Nearby quarry workers didn’t think much of the formations as they blasted rock layers for limestone. And just two years ago, researchers said, highway crews tunneling through hillsides nearly wiped out a major site of dinosaur tracks before the national park intervened.

Such disturbances may have something to do with the area’s striking absence of dinosaur bones, teeth and eggs, experts say. For all of the footprints and swim traces found across Bolivia’s Toro Toro, there are virtually no skeletal remains of the sort that litter the peaks and valleys of Argentine Patagonia and Campanha in Brazil.

But the lack of bones could have natural causes, too. The team said the quantity and pattern of tracks — and the fact they were all found in the same sediment layer — suggest that dinosaurs didn’t settle in what is now Bolivia as much as trudge along an ancient coastal superhighway stretching from southern Peru into northwest Argentina.

The range in footprint sizes indicated that giant creatures roughly 10 meters (33 feet) tall moved in a herd with tiny theropods the size of a chicken, 32 centimeters (1 foot) tall at the hip.

In presenting a snapshot of everyday behavior footprints “reveal what skeletons cannot,” said Anthony Romilio, a paleontologist at the University of Queensland in Australia who also did not participate in the study. Just from footprints, researchers can tell when dinosaurs strolled or sped up, stopped or turned around.

It’s not clear why so many dinosaurs roamed the site

But the reason they flocked in droves to this wind-swept plateau remains a mystery.

“It may have been that they were all regular visitors to a large, ancient, freshwater lake, frequenting its expansive muddy shoreline,” offered Romilio.

Biaggi suggested that they were “running away from something or searching for somewhere to settle.”

What’s certain is that research into this treasure trove of a dinosaur tracksite will continue.

“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,” Biaggi said.