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About 3.5 million years ago, 10-foot-tall carnivorous birds with hooked beaks roamed parts of South America in search of prey. Now, researchers have found a nearly complete skeleton of a new species of these so-called terror birds, and are learning surprising details about their hearing and anatomy.

Researchers found the fossil in 2010 on a beach in Mar del Plata, a city on the eastern coast of Argentina. To their delight, the fossil is the most complete skeleton of a terror bird ever found, with more than 90 percent of its bones preserved, said the study's lead researcher, Federico Degrange, an assistant researcher of vertebrate paleontology at the Centro de Investigaciones en Ciencias de la Tierra and the Universidad Nacional de Córdoba in Argentina.

The scientists named the new species Llallawavis scagliai: "Llallawa" because it means "magnificent" in Quechua, a language native to the people of the central Andes, and "avis," which means "bird" in Latin. The species name honors the famed Argentine naturalist Galileo Juan Scaglia (1915-1989). [Images: 25 Amazing Ancient Beasts]

The skeleton of the new species of terror bird, known as Llallawavis scagliai, is on display at the Museo Municipal de Ciencias Naturales Lorenzo Scaglia in Mar del Plata, Argentina. M. Taglioretti and F. Scaglia

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The specimen is the first known fossilized terror bird with a complete trachea and complete palate (the roof of the mouth). It even includes the intricate bones of the creature's ears, eye sockets, brain box and skull, providing scientists with an unprecedented look at the flightless bird's sensory capabilities.

An analysis of L. scagliai's inner ear structures suggests the terror bird heard low-frequency sounds, an advantage for predators that hunt by listening for the low rumble of their prey's footsteps hitting the ground, the researchers said. The new findings also suggest that the terror bird communicated using low-frequency noises, the researchers added.

"That actually tells us quite a bit about what the animals do, simply because low-frequency sounds tend to propagate across the environment with little change in volume," said Lawrence Witmer, a professor of anatomy at Ohio University who has worked with Degrange before, but was not involved in the new study.

More Video: How a Terror Bird Used Its Beak

This skill puts L. scagliai in good company. Other animals that can or could hear low-frequency sounds include Tyrannosaurus rex, crocodiles, elephants and rhinos, Witmer said.

The researchers also found that the bird's skull was more rigid than those of other birds. Such a skull could have helped the terror bird slam prey with its large beak.

The findings were published Thursday in the Journal of Vertebrate Paleontology.

— Laura Geggel, LiveScience

This is a condensed version of a report from LiveScience. Read the full report. Follow Laura Geggel on Twitter. Follow LiveScience on Twitter, Facebook and Google+.