The 10 Deadliest Prehistoric Mammals

National Geographic specials often show a pack of fleet, deadly cheetahs preying on a herd of wildebeest. As dangerous as they are, though, these cats would be no competition for the much bigger, deadlier, yet markedly less intelligent mammals of the Cenozoic Era, which ranged from enormous rhinoceroses, pigs, hyenas, and bears to giant whales and saber-toothed tigers. Here's a list of the 10 deadliest mammals of the Cenozoic Era and one Cretaceous beast as well.

01
of 10

Andrewsarchus

Andrewsarchus

Dmitri Bogdanov

Measuring 13 feet from snout to tail and weighing at least half a ton, Andrewsarchus was the largest terrestrial meat-eating mammal that ever lived; its skull alone was two and a half feet long and studded with numerous sharp teeth. Oddly enough, though, this Eocene predator wasn't ancestral to modern predators such as wolves, tigers, or hyenas, but belonged to the same general family (artiodactyls, or odd-toed ungulates) as camels, pigs, and antelopes. What did Andrewsarchus eat? Scientists aren't certain, but likely candidates include giant turtles and "thunder beasts" like Brontotherium.

02
of 10

Brontotherium

Brontotherium

Nobu Tamura 

Unlike the other mammals on this list, Brontotherium ("thunder beast") was a confirmed herbivore. What made it so deadly was its sturdy nasal horn and two- to three-ton heft, which exceeds the bulk of any modern rhinoceros. Brontotherium so impressed paleontologists that it has been named four times (its now-discarded monikers include Megacerops, Titanops, and Brontops). As big as it was, this Eocene mammal (or one of its close relatives) may have been prey to the slightly smaller Andrewsarchus.

03
of 10

Entelodon

Entelodon

Heinrich Harder 

The Eocene epoch was a good time to be a giant, deadly mammal. In addition to Andrewsarchus and Brontotherium, there was also Entelodon, known as the "killer pig," a cow-sized animal equipped with a bulldog-like build and a dangerous set of canines. Like its fellow megafauna mammals, this half-ton hog-like animal also possessed an unusually small brain, which may have made it more inclined to charge larger, more dangerous rivals.

04
of 10

The Giant Short-Faced Bear

The Giant Short-Faced Bear

 Billy Hathorn/Wikimedia Commons

The cave bear (Ursus spelaeus) gets more attention, but the giant short-faced bear (Arctodus simus) was the more serious ursine menace of Pleistocene North America. This bear could run at 30 or 40 miles per hour, at least in short sprints, and could rear up to its full height of 12 or 13 feet to intimidate prey. Unlike the cave bear, Arctodus simus preferred meat to vegetables. Still, it isn't known if the giant short-faced bear actively hunted its meals or was a scavenger, harvesting the kill of other, smaller Pleistocene predators.

05
of 10

Leviathan

Leviathan

C. Letenneur) 

A 50-foot-long, 50-ton killer whale equipped with 12-inch teeth and a robust mammalian brain, Leviathan was almost on top of the Miocene food chain—its only rival being the 50-foot-long, 50-ton Megalodon, whose status as a prehistoric shark prevents it from being included on this list of mammals. This cetacean's species name (Leviathan melvillei) pays homage to Herman Melville, the author of "Moby Dick." Its original genus name was recently changed to Livyatan, since "Leviathan" had already been assigned to a prehistoric elephant.

06
of 10

Megantereon

Megantereon

 frank wouters/Flickr/Wikimedia Commons

Smilodon, also known as the saber-toothed tiger, is not part of this list. That's because the more menacing saber-toothed cat of the Pleistocene epoch was Megantereon, which was much smaller (only about four feet long and 100 pounds) but also much more agile, and probably capable of hunting in coordinated packs. Like other saber-toothed cats, Megantereon leaped on its prey from high trees, inflicted deep wounds with its extra-long canines, and then withdrew to a safe distance as its victim bled to death.

07
of 10

Pachycrocuta

Pachycrocuta

Tiberio/Wikimedia Commons

It seems that every mammal alive today had a bigger version during the Pleistocene epoch, a million or so years ago. The Pachycrocuta, for example, also known as the giant hyena, looked like a modern spotted hyena blown up to three times its normal size. Like other hyenas, the 400-pound Pachycrocuta probably stole prey from more accomplished predators, but its stocky build and sharp teeth would have made it more than a match for any prehistoric lion or tiger objecting to its presence.

08
of 10

Paranthropus

Paranthropus

Lillyundfreya/Wikimedia Commons

Ancient mammals weren't only deadly by dint of their large sizes or extra-sharp teeth. Paranthropus, a close relative of the better-known human ancestor Australopithecus, was only equipped with a bigger brain and (presumably) faster reflexes. Although Paranthropus subsisted mostly on plants, it may have been capable of banding together and defending itself against the larger, smaller-brained predators of Pliocene Africa, an adumbration of modern human social behavior. Paranthropus was also bigger than most hominids of its day, a relative giant at five feet tall and 100 to 150 pounds.

09
of 10

Thylacoleo

Thylacoleo

 Karora/Wikimedia Commons 

Better known as the "marsupial lion," Thylacoleo is a prime example of convergent evolution at work. Somehow, this relative of wombats and kangaroos evolved to resemble a saber-toothed tiger, only with bigger teeth. Thylacoleo possessed one of the most powerful bites of any animal in its 200-pound weight class, including sharks, birds, and dinosaurs, and it was clearly the apex mammalian predator of Pleistocene Australia. Its closest rival was the giant monitor lizard Megalania, which it may have occasionally hunted (or been hunted by).

10
of 10

Repenomamus

Repenomamus

Nobu Tamura/WIkimedia Commons

Repenomamus ("reptile mammal") is the exception on this list. It's older than its Cenozoic relatives (dating to the early Cretaceous period, about 125 million years ago) and only weighed about 25 pounds (which was still much heftier than most mouse-sized mammals of the time). The reason it merits the appellation "deadly" is that Repenomamus is the only Mesozoic mammal known to have eaten dinosaurs. A fragment of the Triceratops ancestor Psittacosaurus has been found preserved in one specimen's fossilized stomach.