“Big, bad-ass birds” used their beaks like hatchets

Phorusrhacids weren’t your mama’s parakeet. Known as “terror birds,” a recent biomechanical analysis of a fossilized Andalgalornis steulleti skull shows that it used its oversized, hawk-like, hooked beak as a hatchet to kill its prey.

These gigantic, flightless birds roamed South America during the Cenozoic (62-2 million years ago) before ultimately going extinct. The birds had large skulls and massive beaks, standing between 1-3 meters in height. Andalgalornis was a mid-sized terror bird, about 1.5 meters tall and weighing about 45 kg. Although paleontologists knew terror birds were carnivorous, no one knew exactly how they killed their prey.

A group of scientists led by Federico Degrange of the Universidad de la Plata in Argentina analyzed a fossilized skull of A. steulleti, which lived in Argentina approximately 6 million years ago. A CT scan revealed an unusually thick and rigid skull, which gave the skull much more strength in the front-to-back direction. Instead of being light and flexible like most bird skulls, the joints in the Andalgalornis skull were fused together into rigid beams that provided extra strength. This strength was not matched in the left to right direction or the up and down direction, which led the researchers to believe that this bird wasn’t engaging in any mad fights with their prey as their skulls and beaks weren’t strong enough to withstand any risky moves.

Artist's rendering of Andalgalornis attacking its prey. By Marcos Cenizo.

But the extra strength in the front to back direction of the skull did give scientists a clue to how Andalgalornis killed its prey. The researchers created a 3D model of the bird’s skull that could evaluate the amount of stress placed on the bones in different methods of killing. The only method that didn’t result in an overload of stress on the skull was when Andalgalornis used its beak as a hatchet, swining the massive beak down and then withdrawing.

In an interview with Wired magazine, co-author Lawrence Witmer said “CT scanning extinct animals is exciting because you never really know what you’ll find inside. But you don’t need a CT scan to tell that this was one huge, bad-ass bird.”

Indeed, Dr. Witmer. Indeed.

Degrange FJ, Tambussi CP, Moreno K, Witmer LM, Wroe S (2010) Mechanical Analysis of Feeding Behavior in the Extinct “Terror Bird” Andalgalornis steulleti (Gruiformes: Phorusrhacidae). PLoS ONE 5(8): e11856. doi:10.1371/journal.pone.0011856