The Problem of 90 kilogram (200 lb) Eagles.

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From Bioscience, December 1980:

Argentine scientists have unearthed the fossil remains of what Seems to be the world's largest known flying bird, Argentavis magnificens. The bird lived between eight and five million years ago, in the late Miocene era. With a wingspan of 25 feet, the bird measured 11 feet from beak to tail, and weighed in at l6 to 170 lbs. Its first wing bone, the humerus, was approximately 22 inches long.

Paleontologists Kenneth E. Campbell and Eduardo P. Tonni identified the fossil remains at Argentina's La Plata Museum. Working with leg, wing, and skull bones, Campbell and Tonni, have tentatively concluded that the enormous bird probably did more soaring than flapping.

They admit that it seems initially unlikely that a bird of that size could even get off the ground, but believe that the size of the wing bones and their markings indicate that Argenravis magnificens did fly. "It has the right size wing bones, and it has the markings on the wing bones of secondaries, a type of flight feathers," Campbell said. "It's unlikely that a bird would have feathers and wing bones suit- able for flight if it didn't fly."

In the past, there have been larger birds and larger flying animals, but no larger flying birds. Pterosaurs, giant flying reptiles, were the biggest creatures to take off; one pterosaur found in Texas had a wingspan of 30 to 33 feet. The largest previously known flying birds were the North American Teratornis incredibilis and a marine bird calied Osteo dontoris orri. Both had wingspans of almost 16 feet.

Based on his studies of another teratorn fossil, Teratornis merriami, Campbell believes that the teratorns were predators. "The long, narrow hooked beak and the type of jaw mechanism found in this species are similar to those that would be expected of a bird that grabbed small animals with its beak and swallowed them whole," he said.

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