After dinosaurs became extinct, the terror birds arrived.

The fierce-looking creatures had sharp, hooked beaks and long hind legs, and could reach 10 feet in height. A new study describes the exquisitely preserved fossil of a South American terror bird and provides new details about its anatomy. Ninety percent of the fossil is well preserved.

“This is the most complete skeleton found of any terror bird,” said Federico Javier Degrange, a paleontologist at the National University of Cordoba in Argentina and one of the study’s authors.

With the fossil, found in Argentina, Dr. Degrange and his colleagues were able to reconstruct the bird’s skull, voice box, trachea, eye bones and palate.

Described in The Journal of Vertebrate Paleontology, the new species, called Llallawavis scagliai, was about four feet tall. The bird’s inner ear structure suggests it was capable of hearing low-frequency sounds, just as running birds like ostriches and emus do.