Nature sure made some awesome, and awesomely large, predators back in the day. You had your tyrannosaurus rex, megalodon shark, your sabertooth tiger, and even your marsupial lion in Australia, complete with pouch.
Not to be outdone, birds had their own pants-shittingly scary carnivorous megafauna: the terror bird, which roamed the wilds of South America and as far north as Texas and Florida for millions of years from the middle Paleocene to the early Pleistocene, terrorizing all and sundry as the apex predator of an entire continent.
"Terror bird" is the common English name given to a Family of giant, carnivorous, flightless birds, the Phorusrhacidae. This family actually contained numerous species, some as small as only 3 feet (1 meter) tall, but the ones we are really interested in were the freaking massive ones like the 9 foot (2.7 meter) tall Titanis, or the 10 foot (3 meter) tall Kelenken, the largest bird ever known to have existed.
These birds had razor sharp beaks (Kelenken's beak alone was 1.5 feet long), and judging from the contents of their stomachs, ate everything from small rodents and lizards to horses. That's right. Horses.
Oh, and did I mention that scientists have estimated that many of these birds could run up to around 30 miles per hour? Scary.