Even Apex Predators Like ‘Terror Birds’ Had Enemies, Research Suggests

Bite marks on a fossilized leg bone found in South America suggest a crocodile-like creature attacked a massive, meat-eating bird 12 million years ago

Sarah Kuta | Daily Correspondent

July 28, 2025

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“Terror birds” were giant, flightless, meat-eating creatures that roamed what is now South America for millions of years. As their threatening name suggests, these birds were apex predators, using their strong legs and hooked beaks to hunt down prey.

However, even the most fearsome beasts were never totally safe, new research suggests. Writing in the journal Biology Letters last week, researchers described how one “terror bird” that lived 12 million years ago was likely attacked by an enormous crocodile-like creature called a caiman.

The findings are based on a new analysis of fossilized bite marks on the leg bone of a massive terror bird. The bone was initially discovered by a fossil hunter in Colombia nearly 20 years ago, but it wasn’t studied by scientists until more recently. Last year, a team of paleontologists described the fossil for the first time in the journal Papers in Paleontology.

The leg bone, called a tibiotarsus, had four distinctive indentations that researchers assumed were bite marks. Now that they’ve had a chance to investigate the dents more thoroughly, they’ve concluded they were probably made by the teeth of a medium-sized caiman.

They suspect the caiman responsible was probably Purussaurus neivensis, a large, extinct creature that could grow up to 33 feet long, reports Live Science’s Patrick Pester. This particular individual, however, was probably not yet fully grown and measured around 15 feet long.

To evaluate the pits, researchers made a detailed, digital, 3D model of the bone. They also took measurements of the marks, then compared them with the skulls and teeth of various animals that lived in the area at the time.

The researchers didn’t find any evidence of gnawing, which further supports the hypothesis that a caiman had chomped down on it. “Mammals tend to gnaw, whereas reptiles tend to dismember and swallow,” according to a summary of the paper in Nature.

Since the pits showed no signs of healing, the team suggests the bird did not survive the attack. However, it’s also possible that the caiman scavenged the terror bird’s carcass after it had already died from some other cause.

If the caiman did kill the bird, it was probably lying in wait near the edge of a body of water, using a hunting method similar to how modern crocodiles ambush their unsuspecting victims. “I would imagine it was waiting for prey to be nearby,” says lead author Andres Link, a biologist at Colombia’s University of the Andes, to BBC News’ Victoria Gill.

Paleontologists suspect terror birds spent most of their time on land, whereas caimans mostly stuck to the water. However, “nature is always messier than our nice, little, neat boxes,” says Stephanie Drumheller, a paleontologist at the University of Tennessee, Knoxville, who was not involved with the research, to New Scientist’s Jake Buehler.

At some point, the research suggests, the two creatures must have crossed paths, even though they mostly inhabited different ecosystems. In this way, bite marks can provide scientists with “amazing little snapshots into life in the past,” Drumheller adds.

Speaking with BBC News, Link expressed a similar sentiment, adding that “every piece of [an animal’s] body helps us to understand so much about life on the planet in the past.”

“That’s something that amazes me,” he adds, “how one tiny bone can complete the story.”

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.