This animal belongs to a family of birds known as the Phorusrachids,a group of Cenozoic aves that grew to massive proportions. Andalgalornis is one of the better known examples of these birds and hails from Argentina.

Another larger Terror Bird, as they have come to be called, was found in North America. Titanis walleri was the first of these animals to be found with an intact wing. Instead of the extensively fused carpus of most modern day birds Titanis had a mobile thumb with a large claw at it's tip.This may have helped the bird subdue it's prey.

The Phorusrachids are believed to have been predators of the South American pampas.They would have used their massive blade like beaks to slice though the flesh and bone of the hoofed prey animals. They used their clawed wings and powerful legs to help them hold those animals down. Some Terror birds also had a modified inner toe similar to the type found in Dromaeosaurids.

Although it lacked the ability to flex strongly upward it could have conceivably been used to subdue mammalian prey. Terror birds such as Andalgalornis went extinct shortly after the Panamanian land bridge linked North and South America 2.5 million years ago. The last Phorusrachid known is Titanis of the southeastern United States.

And what we think...

It might be the ancestor of ostriches and most larger species of birds that exists today.

Ostriches--- long necks!