Following the extinction of the dinosaurs 65 million years ago, surviving species rapidly radiated across the planet, evolving into myriad bizarre and beautiful forms. In South America, an island continent until three million years ago, many weird and wonderful species emerged and disappeared. Three-toed horses, giant ground sloths, weird-hoofed mammals, giant rodents, and marvelous marsupials called South America home for millions of years.
In this environment, one family of dinosaurs – the birds – ascended to the summit of the food chain. The Phorusrhacids – or “terror birds” – armed with hooked wings, curved beaks, razor-sharp talons and attitudes to match, swiftly filled the niche of the predatory theropod dinosaurs. The earliest species, the Psilopterinae, stood up to three feet tall and hunted small mammals. By 15 million years ago, enormous terror birds prowled the Pampas. Giants like Kelenken guillermoi, Phorusrhacos, and Titanis were the Tyrannosaurus rex of their day. Kelenken stood 10 feet tall, weighed 300 pounds, and wielded an 18-inch-long beak. Its 28-inch skull was so large that it could easily wolf down a pony-size three-toed horse. The large terror birds aggressively pursued the hoofed mammals – the camel-like liptopterns, the horses, and the rhino-sized toxodonts – with lightning speed. It is believed that the largest terror birds could accelerate to 30 miles per hour, and would often do so when hunting their prey. Active predators, they hunted the herds of hoofed mammals and the giant rodents unchallenged for millions of years.
Unchallenged, that is, until the Great American Interchange. The GAI 3 million years ago was one of the most important events in American prehistory, the product of the volcanic formation of Central America. Species from North America, like camels, jaguars, dogs, and saber-toothed cats crossed the new land bridge into South America, resulting in the displacement of many South American species. Unlike South America’s unfortunate marsupials, terror birds, armadillos, and ground sloths endured the interchange, becoming some of the only species to migrate northward into the United States. Titanis fossils have been found in places as distant as Argentina and Florida, a testament to a successful evolutionary design. Despite this success, the last of the terror birds went extinct 1.8 million years ago, though some unproven evidence suggests that they survived until the mass extinction 10,000 years ago.