They are popularly called “terror birds”, and with good reason.
The giant, flightless beasts that roamed South America for more than 50 million years following the demise of the dinosaurs were fearsome predators.
New research shows the birds’ huge beaks could deliver swift and powerful pecks, very probably killing their victims in one blow before ripping the flesh from their bodies.
“They had the full kit,” said palaeoscientist Steve Wroe.
“These birds had enormous beaks with big hooks on the end. But we’ve shown they had to use those beaks with some precision and caution,” Dr Wroe, a researcher from the University of New South Wales, Australia, told BBC News.
Dr Wroe was part of an international team that has been investigating the predatory behaviour of these extraordinary creatures.
Referred to by scientists as phorusrhacids, the birds flourished when South America was an island continent. Ranging in height from under a metre up to three metres (3ft to 10ft), at least 18 species are known to have evolved before the animals became extinct just a few million years ago.
But because nothing on Earth today resembles the terror birds, it has been difficult to say much about their life habits.
To try to get on top of the issue, the team examined the skeleton of one particular creature called Andalgalornis.
This animal lived in northwestern Argentina about six million years ago. It was mid-sized, standing about 1.4m high (4ft 6in) and weighing about 40kg (88lb). Like all the terror birds, its skull was big (37cm; 15in) with a deep narrow bill armed with a hawk-like hook.
The team scanned the skull to picture its internal architecture and then applied an engineering technique known as finite element analysis (FEA) to assess its capabilities.
FEA is a common approach in advanced design and manufacturing that allows engineers to test the performance of load-bearing materials.
It involves creating a computer model of the skull which can then be subjected to the sorts of forces a real skeleton would experience in different types of attack behaviour.
The results demonstrated that Andalgalornis was built to jab at its prey – in much the same way as a technical boxer might make a series of swift, targeted jabs.
Other strategies ran the risk of injury by putting the slender beak under too much stress, the team found.
“It would have used a repeated, rapid strike – a downward strike, using the neck muscles to drive that big spike on the beak into the prey and then pull back and rip,” explained Dr Wroe.
“It was really badly adapted for grabbing an object and shaking it.”
The research is detailed in a new paper in the journal PLoS One. Its lead author is Federico Degrange of the Museo de La Plata/CONICET in Argentina.
He commented: “No one has ever attempted such a comprehensive biomechanical analysis of a terror bird.
“We need to figure out the ecological role that these amazing birds played if we really want to understand how the unusual ecosystems of South America evolved over the past 60 million years.”
Certainly, the terror birds would have had the opportunity to use their particular attack strategy on a remarkable array of animals.
Like the birds themselves, many other heavyweight and unusual-looking beasts emerged during South America’s separation from the North.
These included giant sloths, huge armadillo-like creatures and even 3m-long rodents.