Phorusrhacidae (or 'Terror Birds')

In the wake of the mass extinction 65 million years ago that left all of the non-avian dinosaurs for dead, the Cenozoic period saw the first and only time in Earth's history that BIRDS were the #1 predators on the planet. And no bird was more terrifying than Phorusrhacidae (or Terror Bird, if like me you can't pronounce that mess of consonants either) ---->

With the largest fossil found measuring one of these bad boys at 9.8 feet tall, and beaks at an estimated 18 inches long, scientists have also reached the terrifying consensus that the Terror Bird was carnivorous, and an extremely fast and nimble runner. They inhabited South America and preferred ambush tactics to hunt their prey.

They disappear from the fossil records 1.8 million years ago, and their demise is thought to be the result of climate change in the Andes' Mountain Range, which meant that the forests became open savannahs with less places to sneak around, rendering the Terror Bird's ambush tactics less effective. Just to add to their problems, 3 million years ago the 'Great American Interchange' - the moment where the landbridge betweeen North and South America finally joined - meant that species previously separated by separate land masses were now free to mingle, and predators like Smilodon (see below) challenged the Phorusrhacidae, in what is one of countless examples in the Animal Kingdom of a Whitney/Mariah situation emerging.