Terror birds are a group of extinct apex predators with huge skulls, long legs, and massive, hooked beaks. These carnivorous flightless birds stalked South America until a couple million years ago. And now, researchers examining exceptionally preserved fossils of a new terror bird species reveal unprecedented details about their ability to hunt and to hear. The findings were published in this month’s Journal of Vertebrate Paleontology. 

This near-complete skeleton of a previously unknown species of terror bird (or phorusrhacid) was discovered in Pliocene sediments at the Atlantic cliff of the Pampean Region in Argentina. A team led by Federico Degrange of the Universidad Nacional de Córdoba analyzed the skeleton from head to toe, literally, as well as its phylogenetic relationships. 

The predatory bird was at least 3.3 million years old, weighed about 18 kilograms (40 pounds), and stood at 1.2 meters (4 feet) tall. They named it Llallawavis scagliai. “Llallawa” is magnificent in Quechua, and “avis” means bird. Galileo Juan Scaglia was the director of the Museo Municipal de Ciencias Naturales Lorenzo Scaglia in Mar del Plata, Buenos Aires, where the skeleton is on display.

With more than 90 percent of the skeleton preserved (pictured to the right), this is the most complete terror bird ever discovered. Importantly, this discovery included rarely-preserved parts of the anatomy that played sensory roles: the auditory region of the skull, voice box, and complete trachea (or windpipe), as well as bones that help focus the eyes and the palate. This is the first time that structures indicating hearing sensitivity have been reconstructed for any terror bird. So the team created 3D models of its inner ear based on CT scans of the fossil and of living species. 

Turns out, the average hearing sensitivity of “Scaglia's magnificent bird” was about 2300 Hz. "The mean hearing estimated for this terror bird was below the average for living birds," Degrange explains in a news release. “This seems to indicate that Llallawavis may have had a narrow, low vocalization frequency range, presumably used for intraspecific acoustic communication or prey detection."

Unlike most birds, Science explains, many joints between the bones of a terror bird’s skull are fused—which may have helped them pummel their prey and rip them apart. Furthermore, this new species had a tiny bone that strengthened the connection between its beak and skull, Science News reports, which made them sturdy enough to be used as a hatchet while hunting.

Images: H. Santiago Druetta (top), M. Taglioretti and F. Scaglia (middle), F. Degrange (bottom)