The 10 Deadliest Prehistoric Mammals

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If You See These Prehistoric Mammals - Run!

Thylacoleo (Wikimedia Commons).

We've all seen those National Geographic specials in which a pack of fleet, deadly cheetahs massacres a clueless herd of wildebeest. As dangerous as they are, though, those cats  would be bite-sized hors d'oeuvres for the much bigger, deadlier (and, yes) dumber mammals of the Cenozoic Era, which ranged from plus-sized rhinoceroses, pigs, hyenas and bears to giant whales and saber-toothed tigers. Here's our list of the 10 deadliest mammals of the Cenozoic Era, with one Cretaceous furball thrown in just for fun.

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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 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? We don't know for sure, but likely candidates include giant turtles and "thunder beasts" like Brontotherium (see next slide).

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Brontotherium (Nobu Tamura).

Unlike the other mammals on this list, Brontotherium ("thunder beast") was a confirmed herbivore--what made it so deadly were its sturdy nasal horn and two- to three-ton heft, which outclassed the bulk of any rhinoceros alive today. In fact, Brontotherium has so impressed paleontologists that it has been named no less than four times (its now-discarded monikors include Megacerops, Titanops and Brontops). And as big as it was, this Eocene mammal (or one of its close relatives) may have figured on the lunch menu of the slightly smaller Andrewsarchus (see previous slide).

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Entelodon (Heinrich Harder).

The Eocene epoch was a good time to be a giant, slobbering, deadly prehistoric mammal. In addition to Andrewsarchus and Brontotherium (see previous slides), there was also Entelodon, aka the "Killer Pig," a cow-sized porker equipped with a bulldog-like build and a dangerous set of canines. Like its fellow megafauna mammals, this half-ton hog also possessed an unusually small brain, which may have made it more inclined to charge larger, more dangerous rivals--which is why you don't see many Entelodons today when you visit your local dairy farm.

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The Giant Short-Faced Bear

giant short-faced bear
The Giant Short-Faced Bear (Wikimedia Commons).

The Cave Bear (Ursus spelaeus) gets all the press, but the Giant Short-Faced Bear (Arctodus simus) was the true ursine menace of Pleistocene North America. Not only was this bear capable of running at 30 or 40 miles per hour, at least in short sprints, but it could also rear up to its full height of 12 or 13 feet to intimidate prey--and unlike the Cave Bear, Arctodus simus preferred meat to vegetables. Still, we don't know whether the Giant Short-Faced Bear actively hunted its meals, or contented itself with harvesting the kill of other, smaller Pleistocene predators.

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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. Fittingly, this cetacean's species name (Leviathan melvillei) pays homage to Herman Melville, the author of Moby Dick; somewhat less fittingly, its genus name was recently changed to Livyatan, since "Leviathan" had already been assigned to a prehistoric elephant.

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Megantereon (Wikimedia Commons).

You may be surprised not to find Smilodon, aka the Saber-Toothed Tiger, on this list. That's because the true saber-toothed menace of the Pleistocene epoch was Megantereon, which was much, much smaller (only about four feet long and 100 pounds) but also much, 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 unfortunate victim bled to death.

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Pachycrocuta (Wikimedia Commons).

It seems that every mammal alive today came in bigger packages during the Pleistocene epoch, a million or so years ago. Exhibit A is Pachycrocuta, also known as the Giant Hyena, which looked like a modern spotted hyena blown up to three times its normal size in a photocopy machine. Like other hyenas, the 400-pound Pachycrocuta probably contented itself with stealing 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.

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Paranthropus (Wikimedia Commons).

Ancient mammals weren't only deadly by dint of their large sizes or extra-sharp teeth. Witness Paranthropus, a close relative of the better-known human ancestor Australopithecus, 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 veritable giant at five feet tall and 100 to 150 pounds.

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Repenomamus (Wikimedia Commons).

Repenomamus ("reptile mammal") is the odd mammal out on this list: it's much, much older than its Cenozoic relatives (dating to the early Cretaceous period, about 125 million years ago) and only weighed about 25 pounds soaking wet (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 feasted on dinosaurs: a fragment of the Triceratops ancestor Psittacosaurus has been found preserved in one specimen's fossilized stomach!

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Thylacoleo (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).