Teen in Argentina finds fossil skull of ancient "terror bird"

LOS ANGELES — A teenager in Argentina has discovered the fossil skull of the biggest bird ever found — a swift, flightless predator 10 feet tall that pursued its prey across the steppes of Patagonia 15 million years ago, researchers at the Natural History Museum of Los Angeles County announced Wednesday.

The skull, tapering to a beak curved like a brush hook, belongs to a previously unknown offshoot of extinct birds known as phorusrhacids, or "terror birds."

Weighing perhaps 400 pounds, the bird most likely preyed on rodents the size of sheep that once grazed on the South American grasslands.

"It is an unbelievable creature," said paleontologist Luis Chiappe, director of the museum's Dinosaur Institute, who documented the find in the journal Nature. "This is the largest known bird, with a skull bigger than a horse's head."

Measuring more than 28 inches long, the fossil skull is at least 10 percent bigger than the largest previously known species, Chiappe and his colleagues reported.

Guillermo Aguirre-Zabiala, a high-school student, found the fossil two years ago among the rock outcrops between two houses by the railroad station in his village east of Bariloche, Argentina.

The fossil also is altering how scientists understand the evolution of South America's largest prehistoric predators. Until now, scientists thought that these unusual flightless birds had become more portly and less agile as they evolved into larger carnivores.

The slender leg and foot bones found with the skull, however, closely resemble those of a typical running bird such as an ostrich, the scientists reported.