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10 Giant Mammals that Succeeded the Dinosaurs

The 10 Most Important Giant Mammals of the Cenozoic Era

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The mammals of the Mesozoic Era were small, quivering creatures that kept well out of the way of dinosaurs by living high up in trees--but not so their successors of the Cenozoic, which were free to evolve into giant sizes and fill the ecological niches left open by the extinction of the dinosaurs. Here's a list of the 10 most notable giant mammals that succeeded the dinosaurs.

1. Mammuthus, the Woolly Mammoth

woolly mammoth
Heinrich Harder
Possibly the most famous prehistoric mammal of all time, the Woolly Mammoth was the largest land animal of pre-Ice Age North America and Eurasia, roaming the frozen northern tundra in vast herds. No one is quite sure why this prehistoric elephant went extinct about 10,000 years ago; most likely it was a combination of climate change and overhunting by early human settlers (who would have valued the Woolly Mammoth as much for its shaggy coat and tusks as its meat). Incredibly, it may one day be possible to clone a Woolly Mammoth, assuming its DNA can be recovered intact from a frozen specimen and a fetus gestated by a living elephant. Read more about the Woolly Mammoth

2. Smilodon, the Saber-Toothed Tiger

smilodon
George C. Page Museum
As you may already have known, the deceptively named Smilodon wasn't technically a tiger, an entirely different genus of large cat. Still, this saber-toothed cat was one of the most feared predators of the Pleistocene epoch, and possessed a unique hunting style: Smilodon would lurk in the low branches of trees, pounce on passing megafauna mammals, stab them in the neck with its huge canines, and then withdraw to a safe distance as the unfortunate animal bled to death. It's as yet unknown whether Smilodon hunted in packs, but the recovery of thousands of skeletons from the La Brea Tar Pits is a strong clue that this was a sociable predator. Read more about Smilodon

3. Megatherium, the Giant Sloth

megatherium
Paris Natural History Museum
The poster mammal for Pleistocene gigantism, the giant sloth Megatherium measured about 20 feet from head to tail and weighed in the neighborhood of two to three tons. As big as it was, Megatherium wasn't even the only plus-sized sloth of North and South America: other genera included the comparably sized Eremotherium; the thousand-pound Glossotherium, which was preyed on by the above-listed Smilodon; and the 500-pound Megalonyx, the bones of which were discovered by American founding father Thomas Jefferson. As big and dangerous-looking as they were, though, these sloths were strict herbivores, using their giant, clawed hands to tear down tasty trees. Read more about Megatherium

4. Basilosaurus

basilosaurus
Dmitri Bogdanov
By far the largest prehistoric whale that ever lived, Basilosaurus measured about 60 feet from head to tail and weighed close to 100 tons (putting it in the same class as the prehistoric shark Megalodon, which lived tens of millions of years later). Oddly enough, when its bones were discovered in 1843, paleontologists assumed that Basilosaurus was a marine reptile, hence its ill-fitting name (Greek for "king lizard.") And oddly enough (part two), Basilosaurus is the official fossil of not one, but two states--both Mississippi and Alabama have laid claim to this giant whale, though they have yet to go to war over the exclusive rights. Read more about Basilosaurus

5. Andrewsarchus

andrewsarchus
Dmitri Bogdanov
Everyone assumes the honor belongs to Smilodon, the "saber-toothed tiger," but the fact is that Andrewsarchus was the largest carnivorous land mammal that ever lived. Named after the dashing paleontologist Roy Chapman Andrews, the one-ton Andrewsarchus probably made its living by preying on the huge "brontotheres" (typical genus: Brontotherium) of the late Eocene epoch. However, as with another famous predator, Tyrannosaurus Rex, paleontologists are unsure whether Andrewsarchus was an active hunter or contented itself with scarfing down already-dead carcasses, like the modern hyenas which this ancient mammal so closely resembled. Read more about Andrewsarchus

6. Canis Diris, the Dire Wolf

dire wolf
George C. Page Museum
Next to the gigantic Andrewsarchus (see above), Canis diris was a relative lightweight, only about as heavy as a full-grown human. However, this much later Pleistocene predator was the biggest prehistoric dog that ever lived, outweighing the modern wolves to which it was immediately ancestral. Unlike modern wolves, though, the Dire Wolf had an uncommonly small brain, and there's speculation that (like Andrewsarchus) it may have scavenged prey like a hyena rather than killing it on the fly, like, well, a wolf. By the way, the remains of Canis diris have been found alongside those of Smilodon in the La Brea Tar Pits of Los Angeles! Read more about the Dire Wolf

7. Glyptodon, the Giant Armadillo

glyptodon
Pavel Riha
Possibly the most comical-looking of all giant prehistoric mammals, Glyptodon was the Pleistocene equivalent of a Volkswagen Beetle: this giant armadillo's body was covered by a huge, car-sized shell, and one of its close relatives, Doedicurus, also sported a clubbed tail. (Why did Glyptodon evolve its formidable armament? Well, the only way to kill this one-ton beast would have been to flip it onto its back and dig into its soft belly, not an easy proposition!) As you might expect, the slow-moving Glyptodon was hunted to extinction by early human settlers of South America, some of whom used this mammal's carapace as a form of prefabricated housing. Read more about Glyptodon

8. Indricotherium

indricotherium
Dmitri Bogdanov
As giant prehistoric mammals go, Indricotherium (also known as Paraceratherium) has proven difficult to classify. The largest terrestrial mammal that ever lived, Indricotherium weighed in the neighborhood of 15 to 20 tons; its enormous bulk, as well as its squat, thick body and long neck, made it reminiscent of the huge sauropod dinosaurs that went extinct tens of millions of years before. Technically, Indricotherium was a perissodactyl (odd-toed ungulate), meaning it was distantly related to prehistoric horses; other than that, it represented an evolutionary line that came to a screeching halt by the end of the Oligocene epoch. Read more about Indricotherium

9. Thylacoleo, the Marsupial Lion

thylacoleo
Wikimedia Commons
It's a common misconception that the herbivorous megafauna mammals of Australia were able to grow to huge sizes because of the lack of any natural predators. Thylacoleo (Greek for "marsupial lion") puts the lie to that myth: this 200-pound predator was every bit as dangerous as Smilodon, its distant relative from North America, making up with its sleek, muscular build what it lacked in huge, saber-shaped canines. As dangerous as it was, though, the Marsupial Lion wasn't the apex predator of Pleistocene Australia; that honor belonged to the giant monitor lizard Megalania, some individuals of which weighed as much as two tons. Read more about Thylacoleo

10. Diprotodon, the Giant Wombat

giant wombat
Nobu Tamura
Giant, marsupial predators like Thylacoleo (above) would quickly have starved to death if they didn't have any plus-sized mammals to prey on. That role was at least partially filled by Diprotodon, an enormous wombat (yes, you heard that right) of the Pleistocene epoch that weighed as much as two tons. The bones of the Giant Wombat have been found all over Australia, some of them at the bottom of lakes (the theory is that herds of Diprotodon attempted to walk over the salt-encrusted surface and, well, you know). Like most megafauna mammals, the Giant Wombat was hunted to extinction by early humans anywhere from 40,000 to 10,000 years ago. Read more about the Giant Wombat
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