Evrim Yazgin
Cosmos science journalist
The 12-million-year-old fossil of an extinct, giant, carnivorous bird found in Colombia’s Tatacoa Desert could be the largest member of its kind.
But it was probably killed by something much bigger.
Ancient South America was home to a group of birds known as “terror birds”. These ferocious, feathered hunters belong to the phorusrhacid (FOR-us-RAH-kid) family. They ranged from 1–3m tall. The largest specimens grew up to 350kg – the size of a large Siberian tiger.
Ancestors of terror birds emerged in the Palaeocene period (66–56 million years ago) immediately after the mass extinction at the end of the Cretaceous, taking advantage of the lack of competition from their larger dinosaur cousins.
The oldest terror bird fossils date to 43 million years ago.
Large predatory birds were also prominent in Europe, Australia, Africa and North America.
South America’s terror birds were the apex predators on the isolated continent. But South America’s isolation ended about 3 million years ago. This saw the migration south of North America’s sabre-toothed cats.
There were mammalian predators prior to this, but none reached the size and power of the lion-sized Smilodon. The terror birds weren’t able to adapt fast enough to the new predators on the block. Their numbers dwindled and terror birds disappear from the fossil record about 100,000 years ago.
Seriema are the closest living relatives of the terror birds. At 1–2kg these crane-like birds are large compared to most living today, but are minnows compared to the terror birds.
The new terror bird fossil is described in a paper published in the journal Palaeontology. Its leg bones indicate a bird 5–20% larger than known phorusrhacids. The fossil was discovered nearly 20 years ago but wasn’t recognised as a terror bird until now.
It lived in the middle of the Miocene epoch (23–5.3 million years ago).
“Terror birds lived on the ground, had limbs adapted for running, and mostly ate other animals,” says study lead Siobhán Cooke, an associate professor at John Hopkins University in the US.
But, in a turning of the tables, this bird appears to have been the prey.
The researchers noticed teeth marks in the terror bird’s bones. The likely culprit is an extinct caiman Purussaurus. This species would have been one of the biggest crocodilians ever, growing to about 10 metres long.
“We suspect that the terror bird would have died as a result of its injuries given the size of crocodilians 12 million years ago,” Cooke says.
Most terror bird fossils come from further south on the continent in modern-day Uruguay and Argentina. Finding such a large phorusrhacid so far north helps researchers understand the wildlife of the region 12 million years ago. Now a desert, scientists believe it was once an environment full of meandering rivers.
Alongside the terror bird would have lived primates, hoofed mammals, giant ground sloths and armadillo relatives, glyptodonts, that were the size of cars.
“It’s a different kind of ecosystem than we see today or in other parts of the world during a period before South and North America were connected,” Cooke explains.
Being the first terror bird found in the region suggests the species would have been relatively uncommon among the animals, Cooke says.
“It’s possible there are fossils in existing collections that haven’t been recognised yet as terror birds because the bones are less diagnostic than the lower leg bone we found,” she adds.
