The extinct group of large, mostly flightless predatory birds from Cenozoic South America was known as the terror birds.
Terror birds are the informal name for the family Phorusrhacidae. They occupied the role of major terrestrial predators while South America was geographically isolated for much of the Cenozoic. Members varied greatly in size, from relatively small forms to giants several metres tall. Their large hooked beaks, powerful legs, and strong claws made them well suited to hunting or scavenging.
The group was not made up of one single species. It included several lineages, including the giant Phorusrhacinae and smaller, more lightly built Psilopterinae. Their closest living relatives are thought to be seriemas, long-legged South American birds that still survive today. When the Isthmus of Panama formed about 2.7 million years ago, northern predators entered South America, but competition alone is not considered a settled explanation for terror-bird extinction. Fossils show that some smaller forms survived much later than the largest species.