Like humans, many animal species have evolved over time to adapt to the changing environments around them. Over the millennia, camels that lived in the desert learned how to store fat, some frogs in colder climates could survive getting frozen and revive themselves after thawing, and animals that were once much bigger got smaller due to less oxygen in the atmosphere. Unthinkably, there are a merry band of creatures we would now consider to be harmless or even "cute" that have been transformed from something far more terrifying thanks to that change. Some of even the most famously timid animals were once mighty behemoths, probably capable of beating a fully grown human in a fist-fight, given that they were once all bigger than men. Most of the giant animals on this list roamed the earth long before early Homo Sapiens even began settling into permanent locations. Some of the creatures on this list died millions of years ago, while others survived up until their encounters with humanity. Most of them, however, lived during a period known as the Pleistocene era, which was known for its Megafauna - literally giant animals. Thankfully.