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Terror Birds: Bigger and Faster

25 October 2006 (All day)
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STEPHANIE ABRAMOWICZ

Eeek!
A newly described terror bird munches on a lamb-sized mammal.

Think of an ostrich on steroids, then add the ferocious hunting skills of an eagle. That's roughly the picture of extinct South American birds called phorusrhacids, or terror birds, that lived from 60 million to 2 million years ago. This week in Nature, two paleontologists describe the largest known skull of a terror bird and say that one of the bird's leg bones shows that the predator was quick on its feet as well as deadly.

The specimen was found in 2004 by a high school student in the small Patagonian town of Comallo, Argentina. He brought it to the Paleontology Museum of Bariloche, which contacted Luis Chiappe of the Natural History Museum of Los Angeles County, who has done extensive fieldwork in Patagonia. The skull is complete--a first for giant terror birds. At 71.6 centimeters long, the skull is about 10% larger than that of the previous record holder, a giant terror bird called Brontornis. Like other terror birds, the tip of the beak curves into a deadly hook. "There's little doubt it was used for killing prey and tearing apart chunks of flesh," Chiappe says.

A leg bone, called the tarsometatarsus, was found with the skull. Whereas the same bone in a terror bird called Paraphysornis is only 31.5 cm long, the new leg fossil measures 43.7 cm long. The bone's slenderness indicates that the creature was "a relatively swift runner," Chiappe says. The new find counters the traditional notion that terror birds always became stockier when they evolved to larger sizes, he adds. And big it was: Extrapolating from the leg bone, Chiappe and colleague Sara Bertelli estimate that the newly discovered bird stood 3 meters tall.

Chiappe and Bertelli say the 15-million-year-old fossil is a novel species, but they haven't yet disclosed the name they've picked for it. They'll do that in a longer paper, which they have submitted to the Journal of Vertebrate Paleontology.

Julia Clarke of North Carolina State University in Raleigh notes that the new fossil adds to the diversity of terror birds. "You can have a large animal that's built for speed," she says. Herculano Alvarenga of the Museu de Historia Natural de Taubaté in São Paulo, Brazil, says that terror birds such as Brontornis probably ate carrion, but that the longer-legged ones were good runners and hunters.

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