Friday, October 11, 2013

Really Weird Birds: The Terror Bird

Terror Birds were very large, flightless, carnivorous birds which are now all extinct.  They were the largest group of top predators in South America during the Cenozoic Era (62-2 million years ago). 

Terror Birds ranged in height from about 3 to 10 feet tall.

Image of Terror Bird species Paraphysornis brasiliensis, measuring about 6 feet tall 
These birds had unusually massive skulls and beaks.  The largest bird skull yet found belongs to the Terror Bird species Kelenken guillermoi.  This bird’s skull measures 28 inches long, including its 18 inch beak.  It stood about 9.8 feet tall!

Image of Kelenken guillermoi, largest head of any known bird 
What was the purpose and benefit of having such a large head and large beak?  Surely to capture and kill prey, but how?  One opinion is that they captured prey with their beak and in order to kill it, shook it vigorously until its neck or back broke.  A second opinion is that after capture they would bite straight down on the animal in order to kill it.  A third opinion is that when in pursuit of prey, the bird would hammer and jab its prey at the opportune moment.
In order to figure out which method Terror Birds most likely used, scientists used CT scans of the bird’s skulls and biomechanical computer models highlighting the physical stress put on the bones when executing the different methods of kill.  The method that showed the least stress was pulling back with the neck and hammering prey with the beak.  The scan showed the skull to have rigid beam-like bones where almost all other known birds have flexible joints.  The beams strengthen the skull and beak, making them extremely powerful for up and down jabbing motions.  Scans also revealed a hollow beak.  Models showed that thrashing the head back and forth with a wiggling prey item makes the hollow beak susceptible to breaking; therefore a method most likely not used.

Skull of terror bird species Paraphysornis brasiliensis
The Terror Bird’s legs were well adapted for quick, agile movement.  They most likely chased prey until either it was cornered or worn out; then the Terror Bird would swing its beak down on the animal like a hatchet, over and over again!

All in all, one could easily see how this bird got its name, for it must have been a truly terrifying creature!

Submitted by Sara Oliver, World Bird Sanctuary Naturalist

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