Phorusrhacids ("Rag-Bearers"), or terror birds, were a family of large carnivorous flightless birds that were the dominant predators in South America during the Cenozoic, 62–2 million years (Ma) ago. They were roughly 1–3 meters (3–10 feet) tall. Their closest modern-day relatives are believed to be the 0.8 m-tall seriemas. Titanis walleri, one of the larger species, is known from Texas and Florida in North America. This makes the phorusrhacids only known example of large South American predators migrating north during the Great American Interchange (which occurred after the volcanic Isthmus of Panama land bridge rose ca. 3 Ma ago). It was once believed that T. walleri only became extinct around the time of the arrival of man in North America[1], but subsequent datings of Titanis fossils have failed to provide evidence for their survival more recently than 1.8 Ma ago.[2][3]

A new specimen discovered in Patagonia in 2006 represents the largest bird skull yet found. The fossil has not been formally described but may belong to a new genus or species.[4]

Phorusrhacids are colloquially known as "terror birds", because their larger species were apex predators and the most fearsome carnivores of their habitat (before the arrival of saber-toothed cats 2.5 Ma ago). Their wings had evolved into meathook-like structures that likely could be stretched out like arms to perform a hacking motion which theoretically would help in bringing down prey. Most of the smaller and some of the larger species are believed to have been fast runners.