When we think about frightening, deadly animals, there is a deep bench of beasts from which to choose the most terror-inducing. The first fearsome creatures in the minds of many are sharks, with the great white far and away the most dreaded fish in the sea. Other people picture a pack of wolves when thinking of scary animals. Many consider snakes or venomous spiders the most frightening animals alive. Whichever living creature you most fear, it’s a safe bet that it’s nowhere near as horrifying as a number of creatures that are, fortunately for us, no longer living.

In eons past, a plethora of truly terrifying creatures walked the earth, swam in the seas, and soared overhead. Compared to these horrifying extinct animals, the deadliest creatures of today might even seem rather tame. While I’d still rather not square off with an extant saltwater crocodile or Siberian tiger, I’d choose them and/or any other living animal before I’d want to fight one of these ancient killing machines. Fortunately, last I checked, scientists are still pretty much stuck when it comes to defying the whole space-time continuum thing, so that’s probably not a decision any of us will have to actually face.

15. Sarcosuchus, King of the Crocodilians

The largest living crocodilians today are the fearsome saltwater crocodiles native to northern Australia, southern India, and all the many islands spread out across the ocean and seas in between. But about 112 millions years ago their lived a forebear that could have eaten a saltwater croc for dinner and still asked for seconds. The sarcosuchus was twice the size of biggest crocs and alligators alive today, measuring up to 40 feet long and weighing in around eight tons. Also, a sarcosuchus packed no fewer than 132 teeth into its sizable jaws.

14. Saber-Toothed Cat, Our Ancient Foe

Saber-toothed cats (often but less accurately called saber-toothed tigers) appeared on earth some 42 millions years ago and only died out 11,000 years back, shortly before what we can fairly term the historic period of human life began. But humans — meaning us, the modern homo sapiens — and saber-toothed cats coexisted for tens of thousands of years, except not in the way those cutesy coexist bumper stickers mean, and more in the constant fight to the death way. Most saber-toothed cats were a good deal larger than extant felines, with some weighing in at more than 850 pounds. They were apex predators that would have had just one formidable foe: us. And the odds were often on the cat.

13. Megalodon Monster Shark

It’s hard to adequately stress just how terrifying a megaladon shark would be in the flesh without using lots of expletives, and I’d rather keep this family-friendly, so just insert your own cursing as needed. The name means “big tooth,” and they had around 275 of those choppers in their mouths. But the teeth were hardly all that was big about this ancient shark. Magaladons often had jaws measuring more than 6.5 feet across and could reach a length of 60 feet. Many specimens might have weighed as much as 100 tons. Which is to say 200,000 pounds of shark. Great white sharks? Why, they’re mere pups at just 20 feet in maximum length and the largest weights estimated at 5,000 pounds.

12. Arctotherium, the Giant Bear

On meeting an Arctotherium angustidens, your first thoughts would likely not have been about how cute and cuddly it looked, and more along the lines of : “Whelp, I’m dead now.” These mighty prehistoric bears could weigh as much as 4,000 pounds and may well have been the largest land-based carnivorous mammal ever discovered. On all four legs, an Arctotherium bear might have stood nearly seven feet tall. On its hind legs, it would tower over the tallest human who ever lived, who it would then swiftly murder and eat. The last of these giants lumbered off the planet around 11,500 years ago, so in fact plenty of humans surely were killed and eaten by them.

11. Jaekelopterus, the Largest Arthropod Ever

Members of the extant arthropod family include sea spiders, horseshoe crabs, scorpions, and centipedes. In other words, most arthropods are terrifying and/or gross. It’s OK to say that, because they can’t read and, even if they could, it’s not libel if it’s true. So now that you have the right tone set in terms of arthropods in general, try this out for size: the ancient Jaekelopterus, the largest known member of this phylum, could grow to more than 8 feet in length. Oh, and it had huge claws on the end of 3-foot long arms, too, so that made it even bigger.

10. Daeodon, the Monster Pig

Long before there was man-bear-pig, there was Daeodon, the prehistoric monster pig. Or is that more of a prehistoric monster buffalo? Or like… is that thing bovine? Daeodon was a member of the entelodont family, all member of which have been extinct for millions of years. And that’s good news, because entelodonts are sometimes referred to as “hell pigs” due to their overall size and, in particular, due to their massive jaws and teeth. In fact, the word “daeodon” is created by the fusion of Greek words meaning “dreadful” and “teeth.”

9. Gigantosaurus, Towering Over T-Rex

When you picture a terrifying carnivorous dinosaur, it’s almost surely the tyrannosaurus rex the comes to mind. But when a T-Rex pictured a giant killed death monster, it imagined the gigantosaurus, a mighty beast that measured up to 45 feet in overall length, making the gigantosaurus notably larger than the average tyrannosaur. The two creatures lived nearly 33 million years apart, however, with the T-Rex being the new kid on the block, so there was never a showdown, epic though that would have been. (Like its smaller cousin, gigantosaurus also had comically small arms, by the way.)

8. Pakicetus, Omnivorous and Amphibious

Alright, the pakicetus wasn’t all that large of an animal, and it is hardly the most ferocious looking creature on our list. But this ancient omnivore, which was about the size of a full-grown adult human being, had an ace up its sleeve: it was swift and deadly both on land and in the water. The creature was a swift swimmer and could dive deep while hunting prey, but also had four fully developed legs that could carry it over land at speed. Its teeth rather resembled those of a dog, albeit considerably larger. Interestingly, this legged creature was an ancestor of many of the whales alive today.

7. Pulmonoscorpius, Ancient Scorpion

While most animals that are only a little more than two feet in size are considered small, that can all be relative. Example? When a scorpion measures 28-inches in size, I’d say that’s massive. Thus it is that we can all be glad the Pulmonoscorpius died out about 300 million years ago. Its massive pinchers and venomous stinger could have easily dispatched smaller animals, and could surely deliver plenty of hurt to a human, too. Don’t look at a picture of this thing right before you go to bed.

6. The Titanoboa Super Snake

The fact that the name of this animal means “titanic boa” gives a pretty clear indication of its principal attribute: size. The titanoboa reached lengths greater than forty feet, with many animals possibly reaching fifty feet long. An average weight of a full grown titanoboa was likely 2,500 pounds. (For reference, the largest living snakes, the reticulated python, can reach 30 feet in length and weigh a maximum of approximately 350 pounds.) Don’t worry too much, though, as these reptiles have been extinct since the late paleocene epoch, which ended some 56 million years ago.

5. Dunkleosteus, the Armored Fish

Long, long before dinosaurs ever walked the earth (or swam the seas), there was another massive death dealer on the scene: the Dunkleosteus. This 20-foot long fish had huge plates of bone around the forward section of its body and could likely have endured significant damage during an attack. That is, when it wasn’t busy instantly killing any animal in its way using its huge jaws that created a bite force with 1,660 pounds of pressure. This ancient aquatic denizen didn’t have traditional teeth, but rather sharp beak-like ridges in a set of jaws that it could open and snap closed in an estimated 5o milliseconds.

4. Arthropleura, the Massive Millipede

You can file this one right under N for Nope. The Arthropleura was an ancient millipede-like creature that crawled around on its many legs some 300 million years ago. It measured up to 7.5 feet in length, which is enough to make you stand on a chair despite how many millions of years separate you from this creature. (Also, the thing would simply have climbed up the chair to say hi anyway.) The Arthropleura was an herbivore and couldn’t really have hurt an adult human even if it wanted to, but I still say the hell with this thing, it’s terrifying.

3. Gigantopithecus, the Giant Ape

I hate to be the one to tell you this, but there’s no such thing as Bigfoot. Call it Sasquatch, talk about its cousin the Yeti, or use the Floridian term Skunk Ape; any way you call it, you’re talking about a fantastic; beast. But maybe those mythical apes were inspired by a real behemoth, the Gigantopithecus. This might ape might have gone extinct only about 100,000 years ago after a run lasting nearly nine million years. The Gigantopithecus was almost ten feet tall (when standing, to be clear, which it probably did rarely) and could have weighed up to 1,300 pounds. They were herbivores, but that doesn’t mean one could not have easily pulled off your arms of it wanted to.

2.  Phorusrhacids, the Terror Bird

I’m not being cute, the Phorusrhacid is actually commonly known as the terror bird. Which makes sense, because in the years following the demise of the dinosaurs, they were the apex predator in many parts of the world. Phorusrhacids lived from about 62 millions years ago until one million years ago, an amazing span when compared to most species. They might have reach ten feet in height and could likely run at speeds over 30 miles per hour. These flightless birds had razor sharp talons and powerful beaks, and are a clear link between theropod dinosaurs (think T-Rex) and modern birds (think… African Gray parrot).

1. Phoberomys Pattersoni, Rodents of Unusual Size

You know that flurry of fear you get when a rat runs by your feet? Well, rats are very small. And they usually can’t kill you unless they’re packing a flea infested with yersinia pestis. Here’s another herbivore that probably would not have killed you, at least not for food, but that surely could have had it wanted. The Phoberomys pattersoni was a rodent that lived about eight million years ago, and that measured about ten feet long. And then add a five foot tail. It might have weighed as much as 1,500 pounds and many specimens had teeth that were up to a foot in length.