This Is the Most Complete 'Terror Bird' Ever Discovered

For tens of millions of years, South American ecosystems were dominated by an extraordinary family of predators known as phorusrhacids—or terror birds, as they are aptly nicknamed.

These formidable flightless carnivores bore a striking resemblance to meat-eating dinosaurs and ultimately, shared the same fate. About two million years ago, terror birds vanished from the planet, and only fragmentary skeletons from this exotic group have been recovered.

That's what makes the discovery of a new species of terror bird—dubbed Llallawavis scagliai—so exciting. Over 90 percent of this animal's remains were recovered from a beach near the Argentinian resort town of Mar del Plata, making it by far the most complete skeleton of a terror bird ever found. The specimen is described in a comprehensive study published in the most recent Journal of Vertebrate Paleontology.

"The discovery of this species reveals that terror birds were more diverse in the Pliocene than previously thought," said paleontologist Federico Degrange, the lead author of the study, in a statement. "It will allow us to review the hypothesis about the decline and extinction of this fascinating group of birds."

Not only was the majority of the bird's 1.2-meter-tall frame recovered, but several subtle features were also exquisitely preserved in the fossilization process. For example, though the animal died some 3.5 million years ago, much of its vocal anatomy remains intact, including "the first complete palate" ever found, Degrange told me over Skype.

"It's beautifully preserved for a terror bird," he said. "The complete trachea was found completely ossified—that's also one of the most outstanding discoveries."

Unfortunately, that doesn't mean paleontologists can reconstruct the song of the terror bird per se (if only). But by studying the bird's vocal and auditory anatomy, Degrange and his team concluded that the bird had a mean hearing sensitivity of around 2,300 Hz, suggesting that they may have sung at more baritone pitches than extant birds.

"We cannot know for sure how they sound, but we are able to estimate how precise their hearing was," he told me. "We can say that if a pitch or a tone produced the low frequency that terror birds were capable of hearing, they probably heard it."

"But we will be never sure that that tone corresponds to the song of the Llallawavis because we also need a structure that was not preserved—the syrinx, the singing structure that birds have," Degrange continued. "It seems that in Llallawavis, it was made of soft tissue, and was not preserved."

The most metal digital reconstruction of an extinct animal ever. Credit: Eloy Manzanero/YouTube

While this individual Llallawavis can't sing to us from the Pliocene, other details of its life can be reconstructed from the impeccably preserved fossils. "We have CT scans of [the skull], so we are studying the brain, blood vessels, and nerves of Llallawavis and other phorusrhacids," Degrange told me.

"Another thing we are trying to work with is the flight capabilities of smaller terror birds," he continued. "There is a group of terror birds that weighed ten kilograms at the most, and they have larger wings, proportionally speaking. We want to know if they were able of doing small flights, similar to modern seriemas, the closest [living] relative of the terror birds."

On a broader scale, Degrange hopes that the new species will challenge the prevailing consensus that invading mammals were responsible for ending the great reign of the terror birds.

"The previous idea was that they kind of lost the competition against placental mammals when placental mammals arrived in South America," he said. "But that was based mainly on the low diversity of [terror bird] species that were known at the time."

"But Llallawavis is showing the opposite, that there was high diversity," he added, "so we have to start looking at new hypotheses to evaluate the causes of their extinction."

It's hard to imagine what could be capable of edging out these magnificent avian predators, some of which weighed over 450 pounds and stood ten feet tall. But whatever the cause of their ultimate demise, it's undeniable that terror birds, like dinosaurs, had an incredibly successful run on the planet—and one that paleontologists have only just begun to decipher.