After the extinction of the non-avian dinosaurs about 65 million years ago, the terror birds were the closest the world has ever come to seeing the imposing, predatory “raptors” of the Mesozoic return. One of the most recently-described species, the approximately 15 million year old Kelenken guillermoi, was a roughly ten-foot-tall carnivore with a two-foot skull tipped in a long beak well-suited to tearing flesh. Not every species grew quite so large, but, as a whole, these flightless, hatchet-headed avians came in a variety of sizes and were among the chief predators in prehistoric South America before the coalescence of the Panama land bridge allowed the formidable dogs, bears, and