1. Duck-faced Elephant (Platybelodon grangeri)
Have you ever wondered what an elephant mixed with a duck looked like? Me neither. Way back when (about 4 million years ago), these guys roamed all over the world. Luckily, these elephant-relatives used their scary jaws for good: they used them as shovels to scoop leaves.
2. Super Snake (Titanoboa cerrejonesis)
What's scarier than a 13-foot Boa constrictor? The Titanoboa. Found in Colombia, this terrifying genus of snake lived approximately 60 million years ago. Researchers estimate that the snake, at its largest, could reach 42 feet long and weigh 2,500 pounds.
3. Super Fly (Meganeura monyi)
Most dragonflies are little flying rainbows. Not this guy. These flying terrors had a foot-long wingspan. This monster of a fly was larger than your head.
4. The Colossal Sea Scorpion (Jaekelopterus rhenaniae)
This 8-foot monster was only recently discovered in Germany. Not only did this crocodile-sized scorpion have 18-inch spiked claw, but it also enjoyed eating its own kind. Eat or be eaten, right?
5. Real Big Bird (Dinornis robustus)
Known as the Giant Moa, this bird is said to be the tallest bird to have ever existed. Previously thought to have been related to its miniature doppelgänger, the kiwi, this flightless bird stands alone — at 12 feet tall. With its rending talons, sharp beak, and long legs, let's thank our lucky stars this thing doesn't exist anymore.
6. Devil Dragon (Megalania prisca)
It's no surprise that this guy's nickname is "the devil dragon." Maxing out at 25 feet, this bad boy is said to be the largest ground-dwelling lizard that's ever lived. The bones that were found in Australia were determined to be only 300 years old and some locals claim some are still out there. Did you just get shivers too?
7. Super Centipede (Arthropleura)
Meet the original Mr. Centipede. Known as the largest land invertebrates ever, these guys could grow up to over 8 feet in length. It could stand up, anchored by its bottom half. Time to look fear in the face. Literally.
8. Gentle Giant Sloth (Megatherium americanum)
These giant versions of the cuddly sloths we know today were also considered herbivorous, though some specialists believe that their long forearms and long, sharp talons could have meant it ate meat. This cuddly giant went extinct about 2,000 years ago and stood 20 feet tall, weighed in at almost 4 tons, and walked on its hind legs. It's kind of hard to believe this guy is related to the armadillo.
9. Swimming Nightmare (Dunkleosteus terrelli)
This giant fish was not only 30 feet long, it's known as one of the fiercest and most terrifying creature to have ever lived. It was so badass that it didn't need teeth, just huge, razor-sharp jaws that could snap any prehistoric shark in two. Oh, and while this guy wasn't eating, he would rub his jawbones together like self-sharpening scissors. Yikes!
10. Titan Of Turles (Protostega gigas)
These guys aren't exactly your first grade pet. The Super Turtle was more than 10 feet in length. Their sharp beaks and strong jaws helped them munch on slow-moving fish, but they weren't much faster themselves; most of the time they were shark bait.
11. Nightmare Bear (Arctodus Simus)
The short-faced bear was a monstrous 11.5 feet tall on its hind legs. This killer had a hunting range of over 200 square miles and 8-inch-long claws. Better start running!
12. Super Croc (Sarcosuchus imperator)
Sarcosuchus imperator is Latin for "flesh crocodile," but now it simply goes by the name "SuperCroc." Now, the crocs in the Nile are plenty scary, but they've got nothing on this 40-foot beast. Oh, and they ate dinosaurs.
13. Steroid Shark (C. megalodon)
If its 7-inch teeth give you any indication, the great white shark's older brother is not one you would want to mess with. Bigger than a bus, the 50-foot C. megalodon is the largest, meat-eating fish to have ever existed. Picture a bus. Now picture this guy being able to swallow it whole.