Ancient 'terror birds' were giant apex predators. Suspected new species is among the largest ever known

Colombia's Tatacoa Desert is believed to be the northernmost known location for terror birds in South America. (Lokman Ilhan/Anadolu Agency/Getty Images via CNN Newsource)

Millions of years ago, long-legged, big-beaked, meat-eating "terror birds" stalked the Americas. The imposing creatures ruled the roost as top predators of their terrestrial ecosystems, and scientists recently discovered one of the largest terror birds ever unearthed.

When paleontologists analyzed a leg bone from a fossil site in Colombia called La Venta, they identified a terror bird — perhaps a new species — that lived about 12 million years ago and dwarfed many of its South American cousins. It would have topped 8 feet (2.5 metres) in height and weighed about 344 pounds (156 kilograms), scientists reported Monday in the journal Papers in Palaeontology.

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Most of the fossils of extinct terror birds, or phorusrhacids, come from sites in Argentina, and most species weighed between 11 pounds (5 kilograms) and 220 pounds (100 kilograms). "They are the only group of birds that achieved the role of terrestrial apex predators, evolving species that basically conquered South America during the Miocene (about 23.03 million to 5.33 million years ago)," said paleontologist and lead study author Federico Javier Degrange, an independent researcher at the National University of Córdoba in Argentina.

The suspected new species was slightly taller than a terror bird from what's now Brazil called Paraphysornis brasiliensis, which stood nearly 8 feet (2.4 metres) tall. But P. brasiliensis was heavier than the La Venta giant, weighing more than 397 pounds (180 kilograms).

A tropical home

A curator at the Museo La Tormenta in Colombia discovered the leg bone in the Tatacoa Desert nearly two decades ago, but paleontologists were uncertain about what type of animal to which it belonged. However, when Degrange saw the bone for the first time in 2023, the answer was obvious, he told CNN. Degrange has studied terror birds for almost 20 years, and he immediately recognized a structure in the front part of the bone that is only found in birds. And the oblique slant of the structure, among other features, told him that the bone belonged to a terror bird.

While some terror bird fossils have been found in Florida and Texas, the specimen from La Venta is believed to be the northernmost terror bird from South America documented by scientists. The discovery in Colombia suggests that terror birds could thrive in diverse habitats and could help explain how and when phorusrhacids diversified northward, Degrange said.

"Until the recovery of this animal, we had a huge geographical gap between Argentina and Brazil, where other terror birds are known, and in the States," Degrange told CNN. "It tells us that, for terror birds, some species lived in more tropical environments," he added.

The fossil leg bone of an extinct terror bird that was found in Colombia's Tatacoa Desert is shown. (Degrange et al. via CNN Newsource)

Placing terror birds in La Venta "is one step closer to understanding how terror birds finally got to North America," Degrange said.

During the Miocene Period, La Venta's ecosystem was green, lush and humid, with large bodies of water, swamps, forests and grasslands. Hoofed mammals, which massive terror birds would likely have eaten, were common there.

Other neighbors of terror birds would have included armadillo relatives called glyptodonts, a variety of perching and wading birds, and large crocodilians, according to the study.

One such croc, a species of giant caiman measuring about 30 feet (9 metres) long named Purussaurus, left tooth marks gouged into the terror bird's fossilized limb. But it's impossible to say whether the croc chomped on the living bird or scavenged a meal after the bird was dead, Degrange said.

Apex predators

Finding a terror bird in La Venta raises hope for unearthing more terror bird fossils in additional South American locations — perhaps in Chile, said Karen Moreno, an adviser on paleontology at the National Monuments Council in Chile and an assistant professor at the Austral University of Chile's Institute of Earth Sciences. Moreno was not involved in the study.

The find also sheds new light on predator-prey relationships and ecological balance in La Venta's tropical habitat, she added. "We could say that dinosaurs (birds, as such) are still at the top of the food chain in the Miocene of South America," Moreno said in an email.

However, even top predators such as terror birds could still be vulnerable to environmental shifts, which may have eventually wiped out these avian giants.

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"The Miocene is an interesting period with huge climatic, oceanographic and paleogeographical changes," Moreno said. "I think we are still far from answering what caused their extinction."

Another question that researchers are hoping to answer about the bird uncovered in La Venta — and terror birds in general — is how they evolved to become so massive, Degrange said.

"We know that probably one of the drivers that led terror birds to get larger and larger was the competition between species of terror birds — but why that big?" he said. "I really hope to find more parts of the skeleton to better analyze the body size of this animal and the evolution of the whole terror bird group. Because everything about terror birds is fascinating."