A quick look at the skeleton of a terror bird – standing up to 3m tall and topped with a mighty beak that looks like it was built for slicing through girders – will leave nobody wondering how they got their name.
Skeletons are all that remain of these giant, flightless, walking bolt cutters, which stalked South America for 45 million years, until they disappeared about 100,000 years ago. They are not the biggest birds ever to have existed – that title probably goes to the elephant birds of Madagascar or the moas of New Zealand, extinct relatives of ostriches and emus. While terror birds bear a superficial similarity to this group, their closest living relatives are, in fact, two species of seriema, crane-like predatory birds from South America.
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Terror birds, like seriemas, were almost certainly carnivorous. Perhaps the biggest of them all, Kelenken guillermoi, a species unearthed in Argentina, wielded a 72cm-long skull (the biggest of any bird, past or present), of which more than half was made up of a hefty beak with a vicious hook at the tip. It’s not entirely clear how they wielded these enormous protuberances.
They may have used them to kill prey and tear off manageable hunks of flesh and bone in the manner of modern-day raptors. But terror birds’ beaks are remarkably narrow considering their spectacular length and depth. An analysis of their mechanical properties suggests that, while they would have been able to deliver a powerful bite, they were far more fragile in the face of sideways forces.
This has seeded the idea that the birds used their beaks as daggers, immobilising prey with repeated downward stabs. Another possibility is that they specialised in chasing down smaller prey that could be swallowed whole. Either way, they were probably very fast over the ground. Based on anatomical evidence, one species, Mesembriornis milneedwardsi, might have reached 97kph, which is up there with a cheetah.
Did humans meet terror birds?
Biologists have long wondered whether the last of the terror birds would have crossed paths with the earliest humans. Indeed, some have argued that humans hunted them to extinction but, as more fossils are found, it is becoming clear that most of them disappeared before humans arrived in the Americas. A more likely scenario is that they were driven to extinction by competition with large carnivorous mammals, such as dogs, cats and bears, which migrated south from North America when the land bridge between the two continents appeared 2.5 million years ago.
Main image: the terror bird species Titanis/Getty
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