Big bird terrorized South America.

Researchers working in Argentina have discovered fossils that may represent the heftiest flightless bird to ever have roamed the planet.

The fragmentary remains--a nearly complete skull and a foot bone called a tarsometatarsus--belonged to a member of a group of flightless birds called the phorusrhacids, or terror birds. The 72-centimeter-long skull, which has the stout, hooked beak characteristic of these predators, is by far the largest phorusrhacid skull ever found, says Sara Bertelli of the American Museum of Natural History in New York. That dimension suggests that the adult height of the newly identified bird, which lived in Argentina about 16 million years ago, was 2.3 meters, about the size of the tallest pro basketball player.

Although some flightless birds from the fossil record--including New Zealand's moas and Madagascar's elephant birds--were taller than the behemoth that Bertelli and her colleagues have discovered, their heads were smaller and their necks thinner.

The researchers haven't produced an estimate of the terror bird's weight, but it almost surely exceeded the weights of known elephant birds and moas, says team member Luis Chiappe of the Natural History Museum of Los Angeles County in Los Angeles. Scientists have estimated that elephant birds weighed about half a ton.

Phorusrhacids came to dominance in South America after the dinosaurs died out about 65 million years ago. At the time, the continent was an isolated landmass; the land bridge that today links it to North America didn't form until just a few million years ago. During that period of isolation, South America lacked carnivorous mammals, so the terror birds were the continent's top predators until they died out about 3 million years ago.

RUNNING IN CIRCLES

The proportions of carbon and nitrogen isotopes in the collagen extracted from layers of this young mammoth's tusk suggest that mammoths weren't fully weaned until about age 6.

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