Why are the Phorusrhacids the most feared predator of prehistoric times?

The ancient world is full of terrifying monsters. But while most people know a thing or two about the dinosaurs, who ruled the animal kingdom until they went extinct about 65 million years ago, little is known about the predators that replaced them. : the bird of terror.

Officially known as Phorusrhacids, they were famous birds of terror about 60 million years ago in South America. Although many different species have been discovered, the largest species ever discovered can be more than 10 feet (3 meters) tall and weigh more than 1,000 pounds (454kg). They were a nimble predator with a sharp beak, and over time, this raptor quickly became the top hunter of the food chain of their time.

However, like the dinosaurs, the reign of the bird of terror has finally come to an end.

Phorusrhacids terror bird skeleton.

Discovering Phorusrhacids

According to an article published in the Cambridge University Journal of Paleontology, the bird of terror was first described by an Argentine paleontologist named Florentino Amegino in 1887. He and his brother. found several "incomplete" fossils in the Santa Cruz Formation of Patagonia.

Darwin's Door reports that Ameghino named his discovery Phorusrhacos longissimus, believing it to be a raptor akin to an eagle or hawk. However, further discoveries revealed that the terror bird was more closely related to the serima, a South American bird.

Since then, about 20 different species of terror birds have been discovered. Some, like Llallawavis scagliai, discovered in 2010, are relatively small and only 4 feet (1.2 meters) tall. But others, like Kelenken guillermoi, discovered in 2004, are far more terrifying. Kelenken has an amazing height - 10 feet and can weigh over 1,000 pounds.

According to paleontologist Luis Chiappe, who described Kelenken in 2007, its massive skull is 'the largest known skull for terror birds'. "In fact, it was the largest known bird skull of this period," he said.

The Age of Terror Birds

About 60 million to two million years ago, the terror birds once dominated South America, using their size, speed, and powerful beaks to dominate the entire continent.

According to the National Audubon Society, terror birds can't fly, but they can reach speeds of up to 60 miles (nearly 100 kilometers) an hour above ground.

Some scientists have suggested that the terror birds may be vegetarians rather than carnivores. According to Wired, German scientists studied the calcium isotope composition in the bones of terror birds and found that they resembled herbivores rather than carnivores.

The bones of this bird were found in the Santa Cruz Formation in Patagonia.

However, Chiappe told Wired he believes the terror birds are predators. 'It is possible that the biting power of the terror birds is not strong enough, however this makes sense that they may be limited to preying on certain animals, but in my opinion that does not make them become a non-prey bird'.

Scientists may not know exactly what the terror birds ate. But they know better the sound of these giant prehistoric beasts. Researchers were able to reconstruct the bird's inner ear after discovering a well-preserved fossil of Llallawavis scagliali in 2010.

Federico Degrange, co-author of the study on Llallawavis scagliali, explains that he and other researchers compared the inner ear canals of terror birds with those of birds alive today. They found that the cries of the terror birds could sound like the calls of an emu or an ostrich. The Audubon Society describes their call as a 'light growl'.

"We can say that terror birds have low frequency sensitivity - so it seems reasonable to assume that they also produce low frequency sounds," Degrange said.

What happened to the terror birds?

As far as paleontologists know today, the terror bird began to disappear about two million years ago. Many researchers believe that their decline, and eventual extinction, coincided with the formation of the Isthmus of Panama, which connects North and South America.

There is strong evidence that terror birds migrated north, as their fossils have been discovered in Texas and Florida. But then, some suspect, the terror birds met other predators like jaguars and saber-toothed cats and then competed for survival.

'So they face new competition for the same resources,' Chiappe explains. "And combined with changes in climate, they may not have been able to compete with predators from North America and lead to extinction."

These birds can reach speeds of up to 60 miles (nearly 100km) an hour on land.

But not everyone thought that the extinction of the terror bird was as simple as that. Degrange believes the discovery of Llallawavis scagliali is complicated because he thinks the bird is more diverse than researchers previously knew.

'The previous idea was that they lost the competition with mammals from North America. But that was largely based on the low diversity of terror birds known at the time. But with the discovery of Llallawavis, everything is showing the opposite."

In other words, he explains, paleontologists need to start thinking about other reasons why the terror birds went extinct.

Currently, there are still many mysteries about the terrorist bird. Is it really a fearsome carnivore - or is it merely a large, growling herbivore? Does the fusion of North and South America make it obsolete? Or are more complicated factors at play, like climate change?