You'd be forgiven for looking at a pigeon and straining to believe that its ancestors were dinosaurs. This is a creature, after all, that descended from some of the finest killing machines evolution has ever produced to now drink gutter water and assault old people for bread crumbs. But millions of years before birds were bumming for handouts in parks, they had risen right to the top of the food chain. In fact, they filled the vacated niches of their menacing theropod forebears like Velociraptor.

These are the terror birds: scrappy, powerful critters that drove their enormous hooked beaks through small mammals as easily as that guy who put a pickax through my crazy uncle's skull in a bar fight that one time (he survived, and no, I'm not even kidding). The 18 known species, the tallest growing to a staggering 10 feet tall, didn’t bother with flying, instead opting to chase down all those creatures that had only just thrown their good-riddance-to-the-massive-carnivorous-dinosaurs party. The poor things woke up with a hangover, and the hangover was the terror bird.

It was 60 million years ago in South America, which had not yet joined with its northern counterpart, where the terror birds rose to power in isolation as apex predators. Even given their success, their fossils are fragmentary and extremely rare, according to paleontologist Luis Chiappe, who in 2007 described the titanic, strangely boxy noggin of the biggest terror bird ever: Kelenken, named after the fearsome bird spirit of Patagonia’s native Tehuelche people.

To the best of paleontologists' knowledge, terror birds weren't see-through. But then again, no one has definitively disproved that they were see-through. Image: Stephanie Abramowicz, Natural History Museum of Los Angeles County

“It's the largest known skull for terror birds,” he said. “As a matter of fact, it’s the largest known bird skull, period. It’s about two-and-a-half feet long, an enormous, colossal beast with a very big hook at the end of the beak like an eagle.”

From fossils like these, paleontologists reckon that terror birds were no crumb-loving pigeons, and not just because there was no bread back then. While a skull can’t tell us exactly how it killed, for Chiappe, this is clearly the beak of a carnivore.

“I mean, we know that a little parrot, a cockatoo, can take your finger out,” he said. “Imagine what a bird like this could have done, the damage it could have done with just a strike of this massive skull and beak. So that's obviously one very easy way of imagining this is how these animals killed their prey.”

The terror birds called forests their home, likely lying in wait to ambush the many small mammals that proliferated in South America after the fall of the dinosaurs. But their skulls and beaks probably weren’t strong enough to tackle large prey, biomechanical studies have shown. With their massively developed legs, they would have been more than capable of chasing down scampering critters: These were extremely nimble, swift predators, hitting speeds of perhaps 30 mph. (This shouldn’t come as a surprise to anyone who has witnessed the surprisingly frantic, not to mention hilarious, way that ostriches run, like giant 40-mph feather dusters having panic attacks.)

The 2.5-foot-long skull of Kelenken, the largest known species of terror bird. That massive hook led *Kelenken'*s prey to disparagingly refer to the predator as "Captain Hook." The terror bird, they knew, was real sore about being rejected from the armed forces, what with its lack of arms. Image: Luis Chiappe, Natural History Museum of Los Angeles County

At the end of terror bird legs were talons, so it could have been that the beasts fired an initial jab with their beaks, then stood on their prey and rapidly shivved it to death. Or perhaps chomped down on their quarry and shook it until its spine snapped.

And we might also look for clues in the terror birds’ living cousins, the seriemas, for further speculation. These South American birds are only a couple of feet tall, but are nonetheless adept hunters, snagging lizards and rodents and such with their talons and bashing them on rocks to shatter their bones.

I included this fairly ugly photograph because it’s so crummy that it almost makes the terror bird look real, like bigfoot in that grainy video. Also, I like how disgusted this guy is by his creation. Such is the tortured existence of the artist, I suppose. Image: Wikimedia

It’s even been suggested that the terror birds weren’t terrors at all. Instead, they were full-blown vegetarians, terroir birds, if you will. Last year, German scientists announced the results of a geochemical analysis of terror bird bones, finding that their calcium isotope compositions aligned them more with herbivores than carnivores.

But Chiappe dismisses the notion that such a powerfully built creature was anything but a predator. The terror birds, he argues, sported truly massive heads relative to body size, much like modern eagles and very much unlike modern omnivorous terrestrial birds like emus and ostriches and cassowaries.

“I think that personally you can come up with all these very rather innovative views, but I think that it makes a lot of sense that these animals were predators,” he said. “It’s just the same when someone came up with the idea that T. rex was a scavenger. I'm sure they ate dead meals, but I'm sure it killed.”

“Maybe [the terror birds’] bite force was not strong enough,” he added, “maybe they were limited to preying on certain animals, but that doesn't make them in my opinion a non-predatory bird.”

A terror bird freaks right out about how poorly its shadow was drawn. Image: Wikimedia

Whatever their diet, and whatever their methods of feeding, the empire of the terror birds entered a slow decline starting around 4.5 million years ago, when the Central American isthmus formed, joining two heretofore self-contained continents. All those creatures that had evolved in isolation for millions of years now found themselves mingling and schmoozing and shaking hands – with their teeth.

Terror birds made their way up into what is now the southern United States, while North America’s top predators – bears and big cats – colonized South America. “So they had to face new competition for the same resources,” said Chiappe, “and that combined with perhaps changes in climate they may not have been able to cope with and that may have impacted their hunting strategies, probably drove them to extinction.”

And so it is that there’s never been a bird, no matter how terrifying, that a cat couldn’t somehow keep in check. In a way it was a lot like the eternal struggles of Sylvester and Tweety, only with, you know, more murder and fewer speech impediments.

Browse the full Absurd Creature of the Week archive here. Have an animal you want me to write about? Email matthew_simon@wired.com or ping me on Twitter at @mrMattSimon.

References:

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

Bertelli, S., Chiappe, L. M., Tambussi, C. P. (2007) A new phorusrhacid (Aves, Cariamae) from the middle Miocene of Patagonia, Argentina. Journal of Vertebrate Paleontology 27:409–419.