Some prehistoric creatures look like they come straight from your nightmares. But of course, those are the COOLEST prehistoric animals! From dinosaurs like the T-Rex and the Triceratops, to underwater monsters like the monster shark himself Megalodon, to other famous extinct animals like the Woolly Mammoth and the Saber-Toothed Tiger, WatchMojo takes a look at the many terrifying prehistoric creatures that make us glad we’re alive today.