César Perdomo, a rancher and fossil hunter in the Tatacoa Desert in Colombia, with a terror bird fossil. Until his find, little was known about how these carnivores spread across the Americas millions of years ago. 

Where There’s Joy in a Terror Bird

by · NY Times

César Perdomo’s small paleontological museum, La Tormenta, is a work in progress. A bare cement structure built on a windswept platform in the Tatacoa Desert, it offers a panoramic view of shallow, craggy canyons carved from soft mudstone.

Inside the museum, fossils are laid out on tables and shelves. The rest of Mr. Perdomo’s collection sits in boxes stacked to the ceiling; a saddle hangs haphazardly above a fossil turtle carapace parked on the floor. Also on-site are a restaurant and several rustic cabins, but weeks can go by without a guest.

Mr. Perdomo, 44, is a longtime rancher who, like many people in this region, has collected fossils all his life. The Tatacoa Desert is home to rich deposits of fossils from about 13 million years ago, the height of the Middle Miocene epoch.

The non-avian dinosaurs were long dead by then, and South America was an island continent, not yet connected to North America. It belonged to oversize hoofed mammals like toxodonts, distant relatives of today’s rhinoceroses and tapirs; tall crocodiles that walked on land; thickly armored armadillo-like creatures called glyptodonts; and giant, flightless birds known as terror birds, with powerful legs and flesh-ripping beaks.

It was a unique time in geological history when birds enjoyed a glorious role as top predators. About 20 terror bird species have been identified from the fossil record. The smallest were no bigger than dogs, while others reached 10 feet tall. Some hunted by ambushing their prey, while others outran it.

Fossils of terror birds have been found in the southern cone of South America, mostly in Argentina, and also in Florida and Texas. Yet despite a century of intensive explorations by paleontologists, they had never been found in between. Their movements and whereabouts were a mystery until Mr. Perdomo decided to build La Tormenta.

‘Rocks’ and toxodont teeth

Mr. Perdomo with a digging bar used to excavate fossils. He learned his techniques from Japanese and American paleontologists who visited in the 1980s and 1990s.

As a young boy in the desert, already herding his own goats, Mr. Perdomo tagged along with two long-running research expeditions led by Kyoto University, in Japan, and by Duke University, in North Carolina. During the 1980s and 1990s, Mr. Perdomo helped the scientists on their annual visits, and in turn learned their digging and preserving techniques. He kept his growing collection of ancient turtle scutes and curved toxodont teeth under his bed. Every so often, his mother threw out his “rocks.”

In the mid-1990s, the foreign paleontologists pulled out of Colombia, fearful of worsening guerrilla and paramilitary activity in the region. “I was excited when they left, knowing that when they came back, I would have new material to show them,” Mr. Perdomo said of the researchers. “But they never came back, never. I held on for a long time to the hope that they would.”

Mr. Perdomo continued collecting, alone, with no books or references to guide him — just memories from the expeditions. As a grown man, he raised cows and kept bees that produced a dark, delicious desert honey. He hunted for fossils in the afternoons, when the heat abated. His techniques grew more refined and his finds more intriguing, although most of them stayed under his bed.

Eventually, professional paleontologists did return, but this time they were Colombian. In 2010, Andrés Link of the Universidad de Los Andes in Bogotá started coming with colleagues and students, and raising funds for different projects. A few years later he met and befriended Mr. Perdomo. “I couldn’t believe that here was this guy, who at age 8 or 9 went around with the Kyoto and Duke expeditions,” Dr. Link recalled. “But he knew where the fossils were.”

In 2015, the Tatacoa Desert was hit by a catastrophic drought that killed more than 10,000 cows. The painful experience of watching his herd wither and die caused Mr. Perdomo to seek other ways to make a living. And as it happened, a local paleontological renaissance was underway.

Two fossil-hunting brothers had opened a small but sophisticated natural history museum in La Victoria, a town on the desert’s northern edge. In the town of Villavieja, to the south, a municipal museum was revamping its fossil displays to make them more scientific and appealing.

Dr. Link and Mr. Perdomo decided to organize, catalog and display Mr. Perdomo’s growing collection, opening it to scientists and anyone else who wanted to see it. In 2019, they began building La Tormenta. Before they were done, a storm whipped through and carried off the museum structure, “like in ‘The Wizard of Oz,’” Dr. Link recalled. The fossils were left soaked but salvageable.

They started over, this time with sturdier materials. The museum wasn’t yet finished last November when Rodolfo Salas, a crocodile specialist from Peru, came by with Dr. Link to check out Mr. Perdomo’s bones.

“César and I were sitting there,” Dr. Link recalled, when a chunky specimen, about five inches long, caught the visiting researcher’s attention. It wasn’t from a mammal, Dr. Salas assured his hosts, and it wasn’t from a reptile. The fossil, which Mr. Perdomo had collected 15 years earlier while repairing a fence, was the tibiotarsus, or upper leg bone, of a bird. An enormous, powerful bird.

An apex predator

The Tatacoa Desert is flanked by two Andean mountain ranges, the Central and Eastern Cordilleras. During the Middle Miocene, the region was a mostly humid landscape of forests, swamps and rivers. As the Andes began emerging 10 million years ago, the rivers were cut off and the region dried up. Sediments flowing from the rising mountains created exceptional conditions for fossils.

The fossil beds, known to paleontologists as the La Venta deposits, offer a rare snapshot of South American life before the animals of this formerly isolated world met those of North America in what scientists call the Great American Biotic Interchange. This took place about five million years ago, as animals began moving in both directions across the fully formed Isthmus of Panama. Terror birds held on for several million more years before becoming extinct, most likely outcompeted by big cats and canines.

When Dr. Link first called about Mr. Perdomo’s specimen, Federico Degrange, a paleontologist at the Argentine science agency CONICET who is the world authority on terror birds, didn’t need to go to Colombia to know that he was dealing with something remarkable.

From the 3-D images that Dr. Link sent, Dr. Degrange determined that the fossil had come from a bird at least 10 percent larger than the two biggest cursorial, or running, terror bird species known to date: Titanis walleri, from North America, and Kelenken guillermoi, from Patagonia.

Dr. Degrange was not sure if this was an extra-large Titanis or Kelenken, or if it was a new species — though he suspected it was new. Amazingly, the leg bone also had marks from a crocodile bite. It was unclear whether the terror bird died in a battle or the crocodile had happened upon its dead remains.

The finding offers a new perspective on the La Venta ecosystem, said Dr. Degrange, who is the lead author, along with Dr. Link and Mr. Perdomo, of a new paper describing the fossil, published in the journal Papers in Paleontology.

“This was an apex predator,” Dr. Degrange said. “It preferred open areas. Before this discovery, most of the remains from La Venta indicated that it was a tropical forest environment. This suggests it was instead a mixture of open areas, shrubbery and forests” — much like Southern Argentina during the Middle Miocene.

Siobhan Cooke, a paleontologist at Johns Hopkins University who is also an author on the paper, said the finding “confirms that terror birds were part of the faunal community at La Venta for some time, not something transient.” The fossils found in Texas and Florida, in other words, “weren’t birds from Patagonia that decided to walk north 5,000 miles.”

This bird’s enormous size “also speaks to us about the trophic levels” — or food chain — “present at La Venta, and the selective pressures that would allow for ever-increasing body size,” Dr. Cooke said.

Thomas LaBarge, a researcher at Indiana University Bloomington who was not involved with this paper, recently published a study exploring size evolution in terror birds. Using measurements from every fossil he could identify, he tried to discern what factors had contributed to their massive proportions.

The expansion of open grasslands during the Middle Miocene has long been thought to be one of them, along with the absence of large mammalian predators. But it was more than environment and opportunity that drove terror birds to become behemoths, Mr. LaBarge found — it was competition with other terror birds.

“Body size controlled the diversity of birds in terms of how many species could coexist and what roles they were taking,” he said. Two terror bird species of similar size with the same hunting style “could not coexist for more than a couple million years. One or the other would become extinct.”

Terror bird fossils are rare to begin with. To find such a large one, from a site where they have never been recorded, “is incredibly important to understanding how terror birds evolved and spread across the Americas,” Mr. LaBarge said.

Rumors of a skull

For a full week in June, Dr. Link’s students and colleagues, visiting from Bogotá, worked to catalog Mr. Perdomo’s fossils. They spent their afternoons hunched over long tables in the half-finished museum, sorting and labeling as they swatted wasps from their sweaty faces.

While the students toiled, Dr. Link went to grab a plastic box from the stacks. He removed the terror bird fossil, which looked like a knobby turkey leg that had been cut in half. The indentations from the ancient crocodile bite resembled two neat punch-holes.

After his fossil was identified as a terror bird late last year, Mr. Perdomo remembered something from his childhood: He had seen the fossil skull of what he now realized was a terror bird. One of his second cousins, with the help of a local priest, had dug it out and taken it to the museum in Villavieja.

“I was 6 years old, how was I to know what it really was?” he said. But it was obvious that it was some sort of bird. The skull, with its formidable curved beak, had sat for months or maybe longer, unprotected, on the museum’s open tables. And then it disappeared.

The professional paleontologists trusted Mr. Perdomo’s memory; they had relied on it for years to guide their searches. “If César says he saw a beak, he saw it,” said Dr. Cooke, who has worked in the field with Mr. Perdomo and Dr. Link.

Many older desert dwellers remember the Duke and Kyoto University expeditions with mixed feelings. The foreign paleontologists had hired the ranchers as assistants but had not shared much information with them. Valuable fossils had been removed. The Japanese team had even hoisted one very large specimen off the ground with a helicopter, an incident so notorious that local musicians wrote a folk song about it.

But the terror bird skull couldn’t have been taken by the foreign teams, Dr. Link concluded, “because if so, they would have published something.” So what happened to it?

A lifelong torment

Abelardo Soto, Mr. Perdomo’s second cousin, lives alone on a farm where the desert meets the foothills of the mountains.

Mr. Perdomo recommended paying his cousin a visit, but warned that he would try to dodge the subject of the missing fossil because the story embarrassed him. And, indeed, Mr. Soto appeared more interested in walking around his property with a lime attached to a string and dangling it over the ground. He was divining the presence of Indigenous burial sites, he explained. “Look — here’s one,” he said, as the lime bobbed.

After further prodding, Mr. Soto acknowledged having collected the skull, in the late 1970s or early 1980s, with his friend, a priest named Jesús Antonio Munar. They placed it in the museum in Villavieja, a project that he and Mr. Munar started together. “We put them there on the tables,” he said. “And then everyone started donating their fossils. And then there was the whole issue with Munar.”

The fossil-hunting priest, as it happened, was a political militant who stockpiled weapons, kept a mini-Uzi in his car and said Mass wearing a pistol. Eventually he was jailed for his activities. “When he left, everything was stolen, everything was taken,” Mr. Soto said.

Mr. Soto went on to describe the prehistoric creature whose skull he had found. It had huge leathery wings, he declared, and fed its young on cliffs. After a while it became clear that Mr. Soto believed he had found a pterodactyl.

It seemed futile to try to get to the bottom of what had happened to the terror bird skull. Fossils, even obscure ones, were lost or stolen all the time. And in the 1980s in Colombia, with people like Mr. Munar running amok, no one was really paying attention. It could just as well be under some rancher’s bed right now, Dr. Link and Mr. Perdomo agreed.

Before the week was over, Mr. Perdomo, Dr. Link and their colleagues had excavated a beautiful, nearly intact fossil glyptodont from a nearby ranch. Part of its shell had been sticking out of a creek, and the owners of the ranch had covered it with half of a plastic drum to keep their cows from stepping on it.

Anyone who wanted to see or work with this fossil, or that of the terror bird, would have to come to La Tormenta, Dr. Link noted — not like in the old days, when the good fossils left the country.

Soon Dr. Link and his students would return to Bogotá, and Mr. Perdomo would be alone with his fossils. On hot nights, he came out to the museum and slept next to them, just as he had as a child. “That’s how crazy he is,” Dr. Link said admiringly. He added: “Ask him why he calls the museum La Tormenta.”

Mr. Perdomo smiled. It wasn’t just a reference to violent storms, like the one that had carried away the first building, he explained. It was about his lifelong relationship with the fossils all around him.

“Why is it here?” he said. “Am I damaging it? How do I get it out? How do I identify it? You stay awake thinking about these questions. That, to me, is torment.”

Discover More in Health and Science