The 20 Biggest Prehistoric Mammals

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These 20 Giant Mammals Are Guaranteed to Give You Nightmares

indricotherium
Indricotherium (Dmitry Bogdanov).

Although the biggest prehistoric mammals never approached the size of the biggest dinosaurs (which preceded them by tens of millions of years), pound for pound they were a lot more imposing than any elephant, pig, hedgehog or tiger alive today. Here's a slideshow of the Brobdingnagian beasts of the Cenozoic Era, some of which were hunted to extinction by the biggest-brained (if not the biggest, period) mammals of them all, human beings. (See also The 20 Biggest Living Mammals.)

02
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Biggest Terrestrial Herbivore - Indricotherium (20 Tons)

indricotherium
Indricotherium, compared to a human being and an elephant (Sameer Prehistorica).

Of all the prehistoric mammals in this slideshow, Indricotherium (which is also known as Paraceratherium and Baluchitherium) is the only one to have approached the size of the giant sauropod dinosaurs that preceded it by tens of millions of years. Believe it or not, this 20-ton Oligocene beast was ancestral to modern (one-ton) rhinos, albeit with a much longer neck and relatively long, slender legs capped by three-toed feet.

03
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Biggest Terrestrial Carnivore - Andrewsarchus (2,000 pounds)

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Andrewsarchus (Dmitry Bogdanov).

Reconstructed on the basis of a single, enormous skull--discovered by the famous fossil-hunter Roy Chapman Andrews during an expedition to the Gobi Desert--Andrewsarchus was a 13-foot-long, one-ton meat eater that may well have feasted on megafauna mammals like Brontotherium (the "thunder beast"). Given its enormous jaws, Andrewsarchus may also have supplemented its diet by biting through the hard shells of equally gigantic prehistoric turtles!

04
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Biggest Whale - Basilosaurus (60 Tons)

basilosaurus
Basilosaurus (Nobu Tamura).

Unlike the other mammals on this list, Basilosaurus can't lay claim to being the largest-ever of its breed--that honor belongs to the still-extant Blue Whale, which can grow to as much as 200 tons. But at 60 or so tons, the middle Eocene Basilosaurus was certainly the biggest prehistoric whale that ever lived, outweighing even the much later Leviathan (which itself may have tangled with the biggest prehistoric shark of all time, Megalodon) by 10 or 20 tons.

05
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Biggest Elephant - The Steppe Mammoth (10 Tons)

steppe mammoth
The Steppe Mammoth (Wikimedia Commons).

Also known as Mammuthus trogontherii--thus making it a close relative of another Mammuthus genus, M. primigenius, aka the Woolly Mammoth--the Steppe Mammoth may have weighed as much as 10 tons, thus putting it out of reach of any of the prehistoric humans of its middle Pleistocene Eurasian habitat. Sadly, if we ever clone a mammoth, we'll have to settle for the more recent Woolly Mammoth, as no quick-frozen specimens of the Steppe Mammoth are known to exist.

06
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Biggest Marine Mammal - Steller's Sea Cow (10 Tons)

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The skull of Steller's Sea Cow (Wikimedia Commons).

Boatloads of kelp littered the shores of the northern Pacific during the Pleistocene epoch--which helps explain the evolution of Steller's Sea Cow, a 10-ton, kelp-munching dugong ancestor that persisted well into historical times, only going extinct in the 18th century. This none-too-bright marine mammal (its head was almost comically small for its gigantic body) was hunted to oblivion by European sailors, who prized it for the whale-like oil with which they fueled their lamps.

07
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Biggest Rhinoceros - Elasmotherium (4 tons)

elasmotherium
Elasmotherium (Dmitry Bogdanov).

Could the 20-foot-long, four-ton Elasmotherium be the source of the unicorn legend? This gigantic rhinoceros sported an equally gigantic, three-foot-long horn on the end of its snout, which doubtless intimidated (and fascinated) the superstitious early humans of late Pleistocene Eurasia. Like its slightly smaller contemporary, the Woolly Rhino, Elasmotherium was covered with thick, shaggy fur, which made it a prized target for any Homo sapiens in need of a warm coat.

08
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Biggest Rodent - Josephoartigasia (2,000 pounds)

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Josephoartigasia (Nobu Tamura).

You think you have a mouse problem? It's a good thing you didn't live in early Pleistocene South America, where the 10-foot-long, one-ton Josephoartigasia scattered rodent-hating hominids to the top branches of tall trees. As big as it was, Josephoartigasia didn't feed on wheels of brie, but soft plants and fruits--and its oversized incisors were probably a sexually selected characteristic (that is, males with bigger teeth had a better chance to pass on their genes to offspring).

09
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Biggest Marsupial - Diprotodon (2 Tons)

diprotodon
Diprotodon (Nobu Tamura).

Also known by its much more evocative name, the Giant Wombat, Diprotodon was a two-ton marsupial that waddled across the expanse of Pleistocene Australia, nibbling on its favorite snack, the saltbush. (So single-mindedly did this huge marsupial pursue its vegetable prey that many individuals drowned after crashing through the surface of salt-encrusted lakes.) Like the other megafauna marsupials of Australia, Diprotodon thrived until the arrival of early humans, who hunted it to extinction.

10
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Biggest Bear - Arctotherium (2 Tons)

arctotherium
Arctotherium (Wikimedia Commons).

Three million years ago, toward the end of the Pliocene epoch, the Central American isthmus rose up from the murky depths to create a land bridge between North and South America. At that point, a population of Arctodus (aka the Giant Short-Faced Bear) made the trip south, eventually going on to spawn the truly imposing, two-ton Arctotherium. The only thing keeping Arctotherium from supplanting Andrewsarchus (slide #3) as the biggest terrestrial mammalian predator was its presumed diet of fruits and nuts.

11
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Biggest Cat - The Ngandong Tiger (1,000 Pounds)

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The Bengal Tiger, to which the Ngandong Tiger is closely related (Wikimedia Commons).

Discovered in the Indonesian village of Ngandong, the Ngandong Tiger was a Pleistocene predecessor of the still-extant Bengal Tiger. The difference is that Ngandong Tiger males may have grown to a whopping 1,000 pounds, which only makes sense, given that paleontologists have also recovered the remains of plus-sized cows, pigs, deer, elephants and rhinos from this portion of Indonesia--all of which likely figured on this fearsome feline's dinner menu. (Why was this region home to so many oversized mammals? No one knows!)

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Biggest Dog - The Dire Wolf (200 Pounds)

dire wolf
The Dire Wolf (Daniel Reed).

In a way, it's unfair to peg the Dire Wolf as the biggest prehistoric dog--after all, some of the "bear dogs" farther back on the canine evolutionary tree, like Amphicyon and Borophagus, were bigger and fiercer, and able to bite through solid bone the way you would chew a piece of ice. There's no disputing, though, that the Pleistocene Canis Dirus was the biggest prehistoric dog that actually looked like a dog, and was at least 25 percent heavier than the largest dog breeds alive today.

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Biggest Armadillo - Glyptodon (2,000 Pounds)

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Glyptodon (Pavel Riha).

Modern armadillos are tiny, inoffensive creatures that will curl up into softball-sized lumps if you so much as look at them cross-eyed. That's not the case with Glyptodon, a one-ton Pleistocene armadillo roughly the size and shape of a classic Volkswagen Beetle. Amazingly, the early human settlers of South America occasionally used Glyptodon shells to shelter themselves from the elements--and also hunted this gentle creature to extinction for its meat, which could feed an entire tribe for days.

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Biggest Sloth - Megatherium (3 Tons)

megatherium
Megatherium (Sameer Prehistorica).

Along with Glyptodon (previous slide), Megatherium, aka the Giant Sloth, was one of the innumerable megafauna mammals of Pleistocene South America. (Cut off from the mainstream of evolution during much of the Cenozoic Era, South America was blessed with copious vegetation, allowing its mammal population to grow to truly enormous sizes.) Its long claws are a clue that Megatherium spent most of its day ripping the leaves off trees, but this three-ton sloth may not have been averse to feasting on the occasional rodent or snake.

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Biggest Rabbit - Nuralagus (25 Pounds)

nuralagus
Nuralagus (Nobu Tamura).

If you're of a certain age, you may remember the Rabbit of Caerbannog, a seemingly harmless bunny that decapitates a group of overconfident knights in the classic movie Monty Python and the Holy Grail. Well, the Rabbit of Caerbannog had nothing on Nuralagus, a 25-pound rabbit that lived on the Spanish island of Minorca during the Pliocene and Pleistocene epochs. As big as it was, Nuralagus had difficulty hopping effectively, and its ears were (ironically) much smaller than those of your average Easter Bunny.

16
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Biggest Camel - Titanotylopus (2,000 Pounds)

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Titanotylopus (Sameer Prehistorica).

Formerly (and more intuitively) known as Gigantocamelus, the one-ton Titanotylopus ("giant knobbed foot") was by far the biggest camel of Pleistocene Eurasia and North America. Like many megafauna mammals of its day, Titanotylopus was equipped with an unusually small brain, and its broad, flat feet were well-adapted to navigating rough terrain. (Surprisingly enough, camels originated in North America, and only wound up in central Asia and the Middle East after millions of years of peregrination.)

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Biggest Lemur - Archaeoindris (500 Pounds)

archaeoindris
Archaeoindris (Wikimedia Commons).

Given the prehistoric rabbits, rats and armadillos you've already encountered in this slideshow, you probably won't be overly fazed by Archaeoindris, a lemur of Pleistocene Madagascar that grew to gorilla-like sizes. The slow, gentle, none-too-bright Archaeoindris pursued a sloth-like lifestyle, to the extent that it looked a bit like a modern sloth (a process known as convergent evolution). Like many megafauna mammals, Archaeoindris was hunted to extinction by the first human settlers of Madagascar, shortly after the last Ice Age.

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Biggest Ape - Gigantopithecus (1,000 Pounds)

gigantopithecus
Two species of Gigantopithecus, compared to a human being (Wikimedia Commons).

Perhaps because its name is so similar to Australopithecus, many people mistake Gigantopithecus for a hominid, the branch of Pleistocene primates directly ancestral to human beings. In fact, though, this was the largest ape of all time, about twice the size of a modern gorilla and presumably much more aggressive. (Some cryptozoologists believe that the creatures we variously call Bigfoot, Sasquatch and Yeti are still-extant Gigantopithecus adults, a theory for which they have adduced not a shred of credible evidence.)

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Biggest Hedgehog - Deinogalerix (10 Pounds)

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Deinogalerix (Wikimedia Commons).

Deinogalerix partakes of the same Greek root as "dinosaur," and for good reason--at two feet long and 10 pounds, this Miocene mammal was the world's biggest hedgehog (modern hedgehogs weigh a couple of pounds, max). A classic example of what evolutionary biologists call "insular gigantism," Deinogalerix grew to plus sizes after its ancestors were stranded on a group of islands off the European coast, blessed with a) lots of vegetation and b) virtually no natural predators.

20
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Biggest Beaver - Castoroides (200 Pounds)

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Castoroides, the Giant Beaver (Wikimedia Commons).

Did the 200-pound Castoroides, also known as the Giant Beaver, build equally giant-sized dams? That's the question many people ask upon first learning about this Pleistocene mammal, but the truth is frustratingly elusive. The fact is that even modern, reasonably sized beavers are capable of building huge structures out of sticks and weeds, so there's no reason to believe Castoroides would have built Grand Cooley-sized dams--though you have to admit that it is an arresting image!

21
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Biggest Pig - Daeodon (2,000 Pounds)

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Daeodon (Carnegie Museum of Natural History).

It's surprising that no barbecue-minded conservationists have considered "de-extincting" Daeodon, since a single, spitted specimen of this 2,000-pound pig would supply enough pulled pork for a small southern city. Also known as Dinohyus (the "terrible pig"), Daeodon looked more like a modern warthog than your classic farm hog, with a broad, flat, mottled face and prominent front teeth; this megafauna mammal must have been unusually well-adapted to its North American habitat, since various species persisted for over 10 million years!