7 Scary Extinct Animals That Were Absolute Terrors

One of the most dangerous extinct animals was the giant short-faced bear (Arctodus simus). A formidable predator of North and South America, it weighed more than 1,500 pounds (680 kilograms) and stood up to 12 feet tall (3.7 meters) on its hind legs.

The giant bear's massive size and powerful jaw made it one of the most dangerous predators of its time, capable of taking down large prey and competing with other apex predators.

Experts say the animal could probably run faster than 40 mph (64 km/h) to catch its meals. That's similar to the top speed of present-day racehorses, meaning human beings would have had no chance at escaping this prehistoric nightmare.

Paleontologists call the extinct birds of the Phorusrhacidae family in South America the "terror birds," ranking them among the planet's scariest extinct animals.

With powerful beaks and sharp teeth capable of inflicting deadly wounds, these creatures were natural predators, preying on other animals and almost certainly instilling fear in the earliest aboriginal people who might have encountered them.

Imagine a 10-foot-tall (3-meter-tall) Phorusrhacos using its huge beak like a hatchet against its victims. (We'll pass on that experience, thanks.)

The terror birds were mostly flightless, but they made up for their lack of flight with the ability to run up to 60 mph (97 km/h). For reference, ostriches, which are the tallest living birds, max out at 9 feet (2.7 meters) tall and can sprint up to 43 mph (69 km/h).

Among the largest snakes to have ever existed, Titanoboa cerrejonensis is a prehistoric animal straight out of your darkest nightmares. It belongs to the Boidae family of animals, which evolved in North and South America during the Cretaceous period.

This giant snake could reach lengths of up to 42 feet (nearly 13 meters) and weighed over a ton (more than 1,000 kilograms). For reference, even the longest anacondas ever discovered have never surpassed 30 feet (9 meters). The mouth and head alone of the extinct animal may have been longer than 2 feet (0.6 meters).

Titanoboa likely lived in or very near the water, where these extinct animals could ambush and kill other species. Their huge size and powerful bite force allowed them to constrict and consume large prey, making them one of the most dangerous extinct animals of the prehistoric world.

Saber-toothed cats, including the famous saber-toothed tiger (Smilodon fatalis), were powerful predators that lived during the early Miocene and Pliocene epochs. With intimidating incisors measuring about 1 foot (0.3 meters) and a powerful jaw, these creatures were adept at taking down large animals.

Weighing up to 750 pounds (340 kilograms), this extinct animal was a superior hunter, electing to catch its prey off guard versus running it down. While it held the prey with its front legs, it used its sharp teeth to slash the animal's throat or stomach. Then it left its prey to bleed out, returning to feast once the animal was dead.

When thinking about the most dangerous extinct animals, you can't overlook the Megalodon (Otodus megalodon), a giant shark that could reach lengths of up to 60 feet (18 meters), making it a truly formidable predator of the oceans.

This prehistoric shark, which swam in the same waters as large whales, possessed the most powerful bite force of any marine creature in history.

Paleontologists have found its teeth marks on fossilized whale bones, suggesting Megalodon ate the faces off prehistoric sperm whales. And Megaladons weren't picky eaters: These distant relatives of today's great white shark also preyed on baleen whales.

Deinosuchus rugosus, which paleontologists refer to as the "terrible crocodile" or "terror crocodile," easily earns a place on this list of the most dangerous extinct animals. It lived during the Cretaceous period and was once the largest predator in North America.

Deinosuchus grew up to 40 feet (12 meters) long and could range from 13,000 to 15,000 pounds (roughly 6.5 to 7.5 tons), or about the same weight as a fully grown Tryannosaurus rex — another scary extinct animal (although the timelines for these two extinct species did not overlap).

With an incredibly powerful bite force, the Deinosuchus was capable of crushing the bones of even the biggest dinosaurs. It also likely fed on prehistoric birds, turtles, fish and other extinct animals.

In the Carboniferous period, the Arthropleura (Arthropleura armata), a gargantuan millipede, roamed the Earth with between 32 and 64 jointed legs.

This terrifying creature is the largest land invertebrate ever discovered, capable of growing up to 8 feet (2.4 meters) long and nearly 2 feet (0.6 meters) wide, with articulated armored plates covering its entire body. It may have weighed close to 110 pounds (50 kilograms).

Although Arthropleura likely fed primarily on plant matter and maybe smaller invertebrates, its massive size and intimidating appearance make it one of the scariest extinct animals to have ever existed.

We created this article in conjunction with AI technology, then made sure it was fact-checked and edited by a HowStuffWorks editor.