Think of a ostrich on steroids, then put in an eagle’s hunting skills. That the image of South American birds called terror birds, that dwelt from 60 million to 2 million, or phorusrhacids. This week at Nature, two paleontologists describe the largest known skull of a terror bird and state that one of the bird’s leg bones indicates that the predator was fast on its feet as well as deadly.
A high school student in Comallo, Argentina’s Patagonian town discovered in 2004 the specimen. It was brought by him into the Paleontology Museum of Bariloche, which contacted Luis Chiappe of the Natural History Museum of Los Angeles County, who has done extensive fieldwork at Patagonia. At 71.6 centimeters long, the skull is about 10\% bigger than that of the previous record holder, a giant terror bird named Brontornis. Like terror birds, the tip of the beak curves into a deadly hook. “There’s very little doubt it had been used for killing prey and ripping apart chunks of flesh,” Chiappe says.
A leg bone, called the tarsometatarsus, was discovered using the skull. Whereas the same bone at a terror bird named Paraphysornis is simply 31.5 cm long, the leg fossil steps 43.7 cm long. The bone slenderness signals that the monster was “a comparatively swift runner,” Chiappe says. The new uncover counters if they evolved to bigger dimensions, the notion that terror birds constantly became stockier, he adds. And it had been: Extrapolating from Chiappe the leg bone and colleague Sara Bertelli estimate that the bird stood 3 meters tall.