Fossil footprints found in Bolivia reveal dinosaurs

Legend said that the enormous three-toed footprints scattered across the central highlands of Bolivia came from supernaturally strong monsters, capable of sinking their claws even into solid stone.

Then scientists came here in the 1960s and allayed the children’s fears, determining that the strange footprints actually belonged to gigantic two-legged dinosaurs that stomped and splashed more than 60 million years ago, in the ancient canals of what is now Toro Toro, a town and popular national park in the Bolivian Andes.

Now, a team of paleontologists, mostly from Loma Linda University in California, has discovered and meticulously documented 16,600 footprints left by theropods, the group of dinosaurs that includes Tyrannosaurus rex. Their study, based on six years of regular field visits and published last Wednesday in the peer-reviewed journal PLOS One, reports that this find represents the largest number of theropod footprints recorded anywhere in the world.

“There is no place in the world where there is such an abundance of (theropod) footprints,” said Roberto Biaggi, co-author of the study led by Spanish paleontologist Raúl Esperante. “We have all these world records at this particular site.”

Impressions record dinosaur behavior, including attempts to swim

The dinosaurs that ruled the Earth and roamed this region also made awkward attempts to swim here, the study found, scraping up what was soft sediment from the bottom of the lake to leave another 1,378 tracks.

The longest swimming lane studied by the researchers measured more than 130 meters in length. “To date, it remains the longest exposed swim lane in the world,” the authors write in the study.

They pressed their claws into the mud just before the water level rose and sealed their footprints, protecting them from centuries of erosion, the 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, as far as he knows, the number of footprints and trails found in Toro Toro is unprecedented.

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

Footprints face preservation threats

Although they have survived for millions of years, human life has threatened these traces. For decades, farmers threshed corn and wheat on the track-covered plateaus. Workers at the nearby quarry didn’t give the formations much thought as they blasted away layers of rock in search of limestone. And just two years ago, researchers said, crews tunneling through the slopes nearly erased a major dinosaur footprint site before the national park intervened.

According to experts, such disturbances may have something to do with the surprising absence of dinosaur bones, teeth and eggs in the area. Despite all the footprints and swim tracks found in Bolivia’s Toro Toro, there are virtually no skeletal remains of the type that cover the peaks and valleys of Argentine Patagonia and Campanha in Brazil.

But lack of bones could also have natural causes. The team said the number and pattern of the footprints – and the fact that they were all found in the same layer of sediment – suggest that the dinosaurs did not settle in what is now Bolivia but trudged along an ancient coastal superhighway that stretched from southern Peru to northwestern Argentina.

The range in size of the footprints indicated that giant creatures about 10 meters (33 feet) tall moved in packs with small chicken-sized theropods, 32 centimeters (1 foot) tall at the hip.

By presenting a snapshot of everyday behavior, the footprints “reveal what skeletons cannot,” said Anthony Romilio, a paleontologist at the University of Queensland in Australia, who was also not involved in the study. Only from the footprints can researchers tell when dinosaurs walked, sped up, stopped or turned.

It’s unclear why so many dinosaurs roamed the site

But why they flocked to this windswept plateau remains a mystery.

“It is possible that they were all regular visitors to a large, ancient freshwater lake, frequenting its extensive muddy shoreline,” Romilio suggested.

Biaggi suggested that they were “running away from something or looking for a place to settle down.”

What is certain is that research into this treasure trove of dinosaur footprints will continue.

“I suspect this will continue over the years and many more footprints will be found right there on the edges of what is already discovered,” Biaggi said.

Recent discoveries of dinosaur footprints

Researchers have recently unearthed other dinosaur footprints.

In March, scientists in England discover a 650-foot trail of dinosaur footprints made 160 million years ago by enormous sauropod dinosaurs.

In January, British researchers unearthed some 200 dinosaur footprints dating back 166 million years in a find believed to be the largest in the UK. “This is one of the most impressive footprint sites I have ever seen, in terms of the scale and size of the footprints,” Professor Kirsty Edgar, a micropaleontologist at the University of Birmingham, told the BBC. “You can go back in time and get a sense of what it would have been like, these huge creatures just wandering around, minding their own business.”

That discovery was announced just a few months after a team of paleontologists found matching dinosaur footprints on what are now two different continents, separated by thousands of kilometers of ocean.

In October 2023, engineers in the United Kingdom made a “dramatic discovery” of dinosaur footprints that experts believe could be from a mantellisaurus, a type of dinosaur that had only three toes on each foot and moved on its hind legs.