Kelenken the Largest of the Terror Birds

Kelenken Terror BirdKelenken was a large bird (part of the “terror bird” group and the largest of all of them) from South America about 15 million years ago. They stood 10 feet tall and weighed almost 500 pounds. They are the only species of their genus, with their full scientific name being Kelenken guillermoi, named after Guillermo Aguirre Zabala, who discovered the species in 1999 in Argentina. The species wasn’t closely examined and classified until five years later after being taken out of storage. Kelenken is the name of a flying winged demon god in the local Native American religion of the Tehuelche people.


These birds could not fly. They were too large and too heavy for that. They did run quickly, though, and might have hunted in groups, chasing down smaller animals. They were definitely carnivores and has a sharp hook on the end of their beak, the use for which was probably to be able to eat as effectively as animals with sharp canines and incisors could. It is also possible that Kelenken was not a hunter at all, just like recent debates around T. rex suppose that they might not have hunted either. It is possible that they were scavengers and scared other animals away with their large size and threatening characteristics. Scientists have learned from studying their skull, though, that their eyesight would have been sharper than their sense of smell, so they could have had more luck chasing than finding. Nevertheless, specimens of leg bone fossils have shown that they were probably quite fast, even faster than other terror birds.

Kelenken Fossil Skull

Kelenken currently holds the record for the largest skull of the terror birds, at over 2 feet long. More than half of that is beak. This is bigger than their leg bone (the one you can see right above their foot, the tarsometatarsus), which was already elongated for running. They were also slimmer and more graceful than other terror birds, meaning they were more agile.


If you remember a few weeks ago, we talked a little bit about the Great American Interchange, where North and South America were connected via Panama when the isthmus formed volcanically and fauna traveled between the two. Animals from North America, such as bears and cats, increased competition for the birds and so their numbers decreased. There is some evidence that instead of going extinct at this point, the terror birds became smaller (and, presumably, less terrifying) and moved into some lower parts of North America. It is possible (and not unlikely, given our track record) that humans were responsible for their extinction at this point, roughly 6 million years ago.

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by Gypsea

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