Giant Mammal and Megafauna Pictures and Profiles

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The Giant Mammals of the Cenozoic Era

palorchestes
Palorchestes (Victoria Museum).

During the latter part of the Cenozoic Era—from about 50 million years ago to the end of the last Ice Age—prehistoric mammals were significantly bigger (and stranger) than their modern counterparts. On the following slides, you'll find pictures and detailed profiles of over 80 different giant mammals and megafauna that ruled the earth after the dinosaurs went extinct, ranging from Aepycamelus to the Woolly Rhino.

02
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Aepycamelus

aepycamelus
Aepycamelus. Heinrich Harder

Name:

Aepycamelus (Greek for "tall camel"); pronounced AY-peeh-CAM-ell-us

Habitat:

Plains of North America

Historical Epoch:

Middle-Late Miocene (15-5 million years ago)

Size and Weight:

About 10 feet high at the shoulder and 1,000-2,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Large size; long, giraffe-like legs and neck

 

Right off the bat, there are two odd things about Aepycamelus: first, this megafauna camel looked more like a giraffe, with its long legs and slender neck, and second, it lived in Miocene North America (not a place one normally associates with camels, whatever the era!) Befitting its giraffe-like appearance, Aepycamelus spent most of its time nibbling the leaves off high trees, and since it lived well before the earliest humans no one ever attempted to take it for a ride (which would have been a difficult proposition, in any case).

03
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Agriarctos

agriarctos
Agrioarctos. Wikimedia Commons

Name:

Agriarctos (Greek for "dirt bear"); pronounced AG-ree-ARK-tose

Habitat:

Woodlands of western Europe

Historical Epoch:

Late Miocene (11 million years ago)

Size and Weight:

About four feet long and 100 pounds

Diet:

Omnivorous

Distinguishing Characteristics:

Small size; quadrupedal posture; dark fur with white spots

 

About Agriarctos

As rare as it is today, the Giant Panda's family tree stretches all the way back to the Miocene epoch, over 10 million years ago. Exhibit A is the newly discovered Agriarctos, a pint-sized (only 100 pounds or so) prehistoric bear that spent much of its time scampering up trees, either to harvest nuts and fruit or to evade the attention of large predators. Based on its limited fossil remains, paleontologists believe Agriarctos possessed a coat of dark fur with light patches around its eyes, belly and tail--a stark contrast to the Giant Panda, on which these two colors are distributed much more evenly.

(For the record, Agriarctos is no longer the earliest Giant Panda precursor; that honor belongs to Kretzoiarctos, which lived about a million years before. The latest development is that the type species of Agriarctos, A. beatrix, has been "synonymized" with Kretzoiarctos, meaning that most paleontologists no longer consider it a valid genus.)

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Agriotherium

agriotherium
Agriotherium. Getty Images

Name:

Agriotherium (Greek for "sour beast"); pronounced AG-ree-oh-THEE-ree-um

Habitat:

Plains of North America, Eurasia and Africa

Historical Period:

Late Miocene-Early Pleistocene (10-2 million years ago)

Size and Weight:

Up to eight feet long and 1,000-1,500 pounds

Diet:

Omnivorous

Distinguishing Characteristics:

Large size; long legs; dog-like build

 

One of the largest bears that ever lived, the half-ton Agriotherium achieved a remarkably wide distribution during the Miocene and Pliocene epochs, reaching as far as North America, Eurasia and Africa (there are no modern bears indigenous to Africa today). Agriotherium was characterized by its relatively long legs (which gave it a vaguely dog-like appearance) and blunt snout studded with massive, bone-crushing teeth--a hint that this prehistoric bear may have scavenged the already-dead carcasses of other megafauna mammals rather than hunting down live prey. Like modern bears, Agriotherium supplemented its diet with fish, fruit, vegetables, and pretty much any other kind of digestible food it happened across.

05
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Andrewsarchus

andrewsarchus
Andrewsarchus. Dmitri Bogdanov

The jaws of Andrewsarchus—the largest terrestrial mammalian predator that ever lived—were so huge and powerful that, conceivably, this Eocene meat-eater might have been able to bite through the shells of giant turtles,  See 10 Facts About Andrewsarchus

06
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Arsinoitherium

arsinoitherium
Arsinoitherium. London Natural History Museum

Name:

Arsinoitherium (Greek for "Arsenoe's beast," after a mythical queen of Egypt); pronounced ARE-sih-noy-THEE-re-um

Habitat:

Plains of northern Africa

Historical Epoch:

Late Eocene-Early Oligocene (35-30 million years ago)

Size and Weight:

About 10 feet long and one ton

Diet:

Plants

Distinguishing Characteristics:

Rhinoceros-like trunk; two conical horns on head; quadrupedal posture; primitive teeth

 

Although it wasn't directly ancestral to the modern rhinoceros, Arsinoitherium (the name refers to the mythical Egyptian Queen Arsenoe) cut a very rhino-like profile, with its stumpy legs, squat trunk and herbivorous diet. However, what really set this prehistoric mammal apart from the other megafauna of the Eocene epoch were the two large, conical, pointed horns jutting out from the middle of its forehead, which were likely a sexually selected characteristic rather than anything meant to intimidate predators (meaning that males with bigger, pointier horns had a better chance of pairing up with females during mating season). Arsinoitherium was also equipped with 44 flat, stumpy teeth in its jaws, which were well-adapted to chewing the extra-tough plants of its Egyptian habitat circa 30 million years ago.

07
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Astrapotherium

astrapotherium
Astrapotherium. Dmitri Bogdanov

Name:

Astrapotherium (Greek for "lightning beast"); pronounced AS-trap-oh-THEE-ree-um

Habitat:

Plains of South America

Historical Epoch:

Early-Middle Miocene (23-15 million years ago)

Size and Weight:

About nine feet long and 500-1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Long, squat trunk; long neck and head

 

During the Miocene epoch, South America was cut off from the rest of the world's continents, resulting in the evolution of a bizarre array of mammalian megafauna (much like Australia today). Astrapotherium was a typical example: this hooved ungulate (a distant relative of horses) looked like a cross between an elephant, a tapir and a rhinoceros, with a short, prehensile trunk and powerful tusks. The nostrils of Astrapotherium were also set unusually high, a hint that this prehistoric herbivore may have pursued a partly amphibious lifestyle, like a modern hippopotamus. (By the way, Astropotherium's name--Greek for "lightning beast"--seems particularly inappropriate for what must have been a slow, ponderous plant eater.)

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The Auroch

auroch
Auroch. Lascaux Caves

The Auroch is one of the few prehistoric animals to be commemorated in ancient cave paintings. As you might have guessed, this ancestor of modern cattle figured on the dinner menu of early humans, who helped drive the Auroch into extinction. See an in-depth profile of the Auroch

09
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Brontotherium

brontotherium
Brontotherium. Nobu Tamura

Befitting its similarity to the duck-billed dinosaurs that preceded it by tens of millions of years, the giant hooved mammal Brontotherium had an unusually small brain for its size—which may have made it ripe picking for the predators of Eocene North America. See an in-depth profile of Brontotherium

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Camelops

camelops
Camelops. Wikimedia Commons

Name:

Camelops (Greek for "camel face"); pronounced CAM-ell-ops

Habitat:

Plains of North America

Historical Epoch:

Pleistocene-Modern (2 million-10,000 years ago)

Size and Weight:

About seven feet tall and 500-1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Large size; thick trunk with long neck

 

Camelops is famous for two reasons: first, this was the last prehistoric camel to be indigenous to North America (until it was hunted to extinction by human settlers about 10,000 years ago), and second, a fossil specimen was unearthed in 2007 during excavations for a Wal-Mart store in Arizona (hence this individual's informal name, the Wal-Mart Camel). Lest you think Wal-Mart might appropriate Camelops as its official greeter, fear not: the remains of this megafauna mammal were donated for further study to nearby Arizona State University.

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The Cave Bear

cave bear
The Cave Bear (Wikimedia Commons).

The Cave Bear (Ursus spelaeus) was one of the most common megafauna mammals of Pleistocene Europe. An astonishing number of Cave Bear fossils have been discovered, and some caves in Europe have yielded literally thousands of bones. See 10 Facts About the Cave Bear

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The Cave Goat

cave goat
The Cave Goat. Cosmocaixa Museum

Name:

Myotragus (Greek for "mouse goat"); pronounced MY-oh-TRAY-gus; also known as the Cave Goat

Habitat:

Mediterranean islands of Majorca and Minorca

Historical Epoch:

Pleistocene-Modern (2 million-5,000 years ago)

Size and Weight:

About four feet long and 100 pounds

Diet:

Plants

Distinguishing Characteristics:

Relatively small size; forward-facing eyes; possible cold-blooded metabolism

 

You might think it strange that a creature as ordinary and inoffensive as a prehistoric goat would make headlines around the world, but Myotragus merits the attention: according to one analysis, this smallish "Cave Goat" adapted to the sparse food of its island habitat by evolving a cold-blooded metabolism, similar to that of reptiles. (In fact, the authors of the paper compared fossilized Myotragus bones to those of contemporary reptiles, and found similar growth patterns.)

As you might expect, not everyone subscribes to the theory that Myotragus had a reptile-like metabolism (which would make it the first mammal in history to have ever evolved this bizarre trait). More likely, this was simply a slow, stubby, ponderous, small-brained Pleistocene herbivore that had the luxury of not having to defend itself against natural predators. An important clue is the fact that Myotragus had forward-facing eyes; similar grazers have wide-set eyes, the better to detect carnivores approaching from all directions.

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The Cave Hyena

cave hyena
Cave Hyena. Wikimedia Commons

Like other opportunistic predators of the Pleistocene epoch, Cave Hyenas preyed on early humans and hominids, and they weren't shy about stealing the hard-earned kill of packs of Neanderthals and other large predators. See an in-depth profile of the Cave Hyena

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The Cave Lion

cave lion panthera leo spelaea
Cave Lion (Panthera leo spelaea). Heinrich Harder

The Cave Lion came by its name not because it lived in caves, but because intact skeletons have been discovered in Cave Bear habitats (Cave Lions preyed on hibernating Cave Bears, which must have seemed like a good idea until their victims woke up!) See an in-depth profile of the Cave Lion

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Chalicotherium

chalicotherium
Chalicotherium. Dmitri Bogdanov

Why would a one-ton megafauna mammal be named after a pebble, rather than a boulder? Simple: the "chalico" part of its name refers to Chalicotherium's pebble-like teeth, which it used to grind down tough vegetation. See an in-depth profile of Chalicotherium

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Chamitataxus

chamitataxus
Chamitataxus (Nobu Tamura).

Name

Chamitataxus (Greek for "taxon from Chamita"); pronounced CAM-ee-tah-TAX-us

Habitat

Woodlands of North America

Historical Epoch

Late Miocene (6 million years ago)

Size and Weight

About one foot long and one pound

Diet

Insects and small animals

Distinguishing Characteristics

Slender build; good smell and hearing

 

Chamitataxus runs counter to the general rule that every modern mammal had a plus-sized ancestor lurking millions of years back in its family tree. Somewhat disappointingly, this badger of the Miocene epoch was about the same size as its descendants of today, and it seems to have behaved in much the same way, locating small animals with its excellent smell and hearing and killing them with a quick bite to the neck. Perhaps the small proportions of Chamitataxus can be explained by the fact that it coexisted with Taxidea, the American Badger, which still annoys homeowners in the present day.

17
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Coryphodon

coryphodon
Coryphodon. Heinrich Harder

Perhaps because efficient predators were in short supply during the early Eocene epoch, Coryphodon was a slow, lumbering beast, with an unusually small brain that beckons comparison with those of its dinosaur predecessors. See an in-depth profile of Coryphodon

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Daeodon (Dinohyus)

daeodon
Daeodon (Carnegie Museum of Natural History).

The Miocene pig Daeodon (formerly known as Dinohyus) was roughly the size and weight of a modern rhinoceros, with a broad, flat, warthog-like face complete with "warts" (actually fleshy wattles supported by bone). See an in-depth profile of Daeodon

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Deinogalerix

deinogalerix
Deinogalerix (Leiden Museum).

Name:

Deinogalerix (Greek for "terrible polecat"); pronounced DIE-no-GAL-eh-rix

Habitat:

Woodlands of western Europe

Historical Epoch:

Late Miocene (10-5 million years ago)

Size and Weight:

About two feet long and 10 pounds

Diet:

Probably insects and carrion

Distinguishing Characteristics:

Large size; rat-like tail and feet

 

It's true that most mammals of the Miocene epoch grew to plus sizes, but Deinogalerix—perhaps it should be better known as the dino-hedgehog—had an added incentive: this prehistoric mammal seems to have been restricted to a few isolated islands off the southern coast of Europe, a sure evolutionary recipe for gigantism. About the size of a modern tabby cat, Deinogalerix probably made its living by feeding on insects and the carcasses of dead animals. Although it was directly ancestral to modern hedgehogs, for all intents and purposes Deinogalerix looked like a giant rat, with its naked tail and feet, narrow snout, and (one imagines) overall peskiness.

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Desmostylus

desmostylus
Desmostylus. Getty Images

Name:

Desmostylus (Greek for "chain pillar"); pronounced DEZ-moe-STYLE-us

Habitat:

Shorelines of the northern Pacific

Historical Epoch:

Miocene (23-5 million years ago)

Size and Weight:

About six feet long and 500 pounds

Diet:

Plants

Distinguishing Characteristics:

Hippo-like body; shovel-shaped tusks in lower jaw

 

If you happened across Desmostylus 10 or 15 million years ago, you might be forgiven for mistaking it for a direct ancestor of either hippopotamuses or elephants: this megafauna mammal had a thick, hippo-like body, and the shovel-shaped tusks jutting out of its lower jaw were reminiscent of prehistoric proboscids like Amebelodon. The fact is, though, that this semi-aquatic creature was a true evolutionary one-off, inhabiting its own obscure order, "Desmostylia," on the mammalian family tree. (The other members of this order include the truly obscure, but amusingly named, Behemotops, Cornwallius and Kronokotherium.) It was once believed that Desmostylus and its equally strange relatives subsisted on seaweed, but a more likely diet now seems to have been the wide range of marine vegetation surrounding the northern Pacific basin.

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Doedicurus

doedicurus
Doedicurus. Wikimedia Commons

This slow-moving prehistoric armadillo Doedicurus was not only covered by a large, domed, armored shell, but it possessed a clubbed, spiked tail similar to those of the ankylosaur and stegosaur dinosaurs that preceded it by tens of millions of years. See an in-depth profile of Doedicurus

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Elasmotherium

elasmotherium
Elasmotherium (Dmitry Bogdanov).

For all its size, bulk and presumed aggressiveness, the single-horned Elasmotherium was a relatively gentle herbivore—and one adapted to eating grass rather than leaves or shrubs, as evidenced by its heavy, oversized, flat teeth and lack of incisors. See ​an in-depth profile of Elasmotherium

23
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Embolotherium

embolotherium
Embolotherium. Sameer Prehistorica

Name:

Embolotherium (Greek for "battering ram beast"); pronounced EM-bo-low-THEE-ree-um

Habitat:

Plains of central Asia

Historical Epoch:

Late Eocene-Early Oligocene (35-30 million years ago)

Size and Weight:

About 15 feet long and 1-2 tons

Diet:

Plants

Distinguishing Characteristics:

Large size; broad, flat shield on snout

 

Embolotherium was one of the central Asian representatives of the family of large herbivorous mammals known as brontotheres ("thunder beasts"), which were ancient (and distant) cousins of the modern rhinoceros. Of all the brontotheres (which also included Brontotherium), Embolotherium had the most distinctive "horn," which actually looked more like a broad, flat shield sticking up from the end of its snout. As with all such animal accoutrements, this odd structure may have been used for display and/or to produce sounds, and it was doubtless a sexually selected characteristic as well (meaning males with more prominent nose ornaments mated with more females).

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Eobasileus

eobasileus
Eobasileus (Charles R. Knight).

Name:

Eobasileus (Greek for "dawn emperor"); pronounced EE-oh-bass-ih-LAY-us

Habitat:

Plains of North America

Historical Epoch:

Middle-Late Eocene (40-35 million years ago)

Size and Weight:

About 12 feet long and one ton

Diet:

Plants

Distinguishing Characteristics:

Rhino-like body; three matched horns on skull; short tusks

 

For all intents and purposes, Eobasileus can be considered a slightly smaller version of the more famous Uintatherium, yet another prehistoric megafauna mammal that roamed the plains of Eocene North America. Like Uintatherium, Eobasileus cut a vaguely rhino-shaped profile, and had an exceptionally knobby head sporting three matched pairs of blunt horns as well as short tusks. It's still unclear how these "uintatheres" of 40 million years ago were related to modern herbivores; all we can say for sure, and leave it at that, is that they were very large ungulates (hooved mammals).

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Eremotherium

eremotherium
Eremotherium (Wikimedia Commons).

Name:

Eremotherium (Greek for "solitary beast"); pronounced EH-reh-moe-THEE-ree-um

Habitat:

Plains of North and South America

Historical Epoch:

Pleistocene-Modern (2 million-10,000 years ago)

Size and Weight:

About 20 feet long and 1-2 tons

Diet:

Plants

Distinguishing Characteristics:

Large size; long, clawed hands

 

Yet another of the gigantic sloths that prowled the Americas during the Pleistocene epoch, Eremotherium differed from the equally huge Megatherium in that it was technically a ground, and not a tree, sloth (and thus more closely related to Megalonyx, the North American ground sloth discovered by Thomas Jefferson). Judging by its long and arms and huge, clawed hands, Eremotherium made its living by mauling and eating trees; it lasted well into the last Ice Age, only to be hunted to extinction by the early human settlers of North and South America.

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Ernanodon

ernanodon
Ernanodon. Wikimedia Commons

Name:

Ernanodon; pronounced er-NAN-oh-don

Habitat:

Plains of central Asia

Historical Epoch:

Late Paleocene (57 million years ago)

Size and Weight:

About two feet long and 5-10 pounds

Diet:

Insects

Distinguishing Characteristics:

Small size; long claws on front hands

 

Sometimes, all it takes to propel an obscure prehistoric mammal onto the evening news is the discovery of a new, almost intact specimen. The central Asian Ernanodon has actually been known to paleontologists for over 30 years, but the "type fossil" was in such bad shape that few took notice. Now, the discovery of new Ernanodon specimen in Mongolia has cast new light on this strange mammal, which lived in the late Paleocene epoch, less than 10 million years after the dinosaurs went extinct. Long story short, Ernanodon was a small, digging mammal that seems to have been ancestral to modern pangolins (which it probably resembled). As to whether Ernanodon burrowed in search of prey, or to escape the predation of larger mammals, that will have to await future fossil discoveries!

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Eucladoceros

eucladoceros
Eucladoceros. Wikimedia Commons

Name:

Eucladoceros (Greek for "well-branched horns"); pronounced YOU-clad-OSS-eh-russ

Habitat:

Plains of Eurasia

Historical Epoch:

Pliocene-Pleistocene (5 million-10,000 years ago)

Size and Weight:

About eight feet long and 750-1,000 pounds

Diet:

Grass

Distinguishing Characteristics:

Large size; large, ornate antlers

 

In most respects, Eucladoceros wasn't much different from modern deers and moose, to which this megafauna mammal was directly ancestral. What really set Eucladoceros apart from its modern descendants were the large, branching, multi-tined antlers sported by the males, which were used for intra-species recognition within the herd and also were a sexually selected characteristic (that is, males with bigger, more ornate horns were more likely to impress females). Oddly enough, the antlers of Eucladoceros don't seem to have grown in any regular pattern, possessing a fractal, branching shape that must have been an impressive sight during mating season.

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Eurotamandua

eurotamandua
Eurotamandua. Nobu Tamura

Name:

Eurotamandua ("European tamandua," a modern genus of anteater); pronounced YOUR-oh-tam-ANN-do-ah

Habitat:

Woodlands of western Europe

Historical Epoch:

Middle Eocene (50-40 million years ago)

Size and Weight:

About three feet long and 25 pounds

Diet:

Ants

Distinguishing Characteristics:

Large size; powerful front limbs; long, tube-like snout

 

In an odd reversal of the usual pattern with megafauna mammals, Eurotamandua wasn't significantly bigger than modern anteaters; in fact, this three-foot-long creature was considerably smaller than the modern Giant Anteater, which can attain lengths of over six feet. However, there's no mistaking Eurotamandua's diet, which can be inferred from its long, tubular snout, powerful, clawed front limbs (which were used for digging up anthills), and muscular, gripping tail (which held it in place as it settled in for a nice, long meal). What's less clear is whether Eurotamandua was a true anteater, or a prehistoric mammal more closely related to modern pangolins; paleontologists are still debating the issue.

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Gagadon

gagadon
Gagadon. Western Digs

If you're announcing a new genus of artiodactyl, it helps to come up with a distinctive name, since even-toed mammals were thick on the ground in early Eocene North America--which explains Gagadon, named after the pop superstar Lady Gaga. See an in-depth profile of Gagadon

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The Giant Beaver

castoroides giant beaver
Castoroides (Giant Beaver). Field Museum of Natural History

Did Castoroides, the Giant Beaver, build giant dams? If it did, no evidence has been preserved, though some enthusiasts point to a four-foot-high dam in Ohio (which may well have been made by another animal, or a natural process). See an in-depth profile of the Giant Beaver

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The Giant Hyena

giant hyena pachycrocuta
Giant Hyena (Pachycrocuta). Wikimedia Commons

Pachycrocuta, also known as the Giant Hyena, followed a recognizably hyena-like lifestyle, stealing freshly killed prey from its fellow predators of Pleistocene Africa and Eurasia and occasionally even hunting for its own food. See an in-depth profile of the Giant Hyena

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The Giant Short-Faced Bear

giant short-faced bear arctodus simus
The Giant Short-Faced Bear. Wikimedia Commons

With its presumed speed, the Giant Short-Faced Bear may have been capable of running down the prehistoric horses of Pleistocene North America, but it doesn't seem to have been built robustly enough to tackle larger prey. See an in-depth profile of the Giant Short-Faced Bear

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Glossotherium

glossotherium
Glossotherium (Wikimedia Commons).

Name:

Glossotherium (Greek for "tongue beast"); pronounced GLOSS-oh-THEE-ree-um

Habitat:

Plains of North and South America

Historical Period:

Pleistocene-Modern (2 million-10,000 years ago)

Size and Weight:

About 13 feet long and 500-1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Large claws on front paws; large, heavy head

 

Yet another of the giant megafauna mammals that prowled the forests and plains of Pleistocene North and South America, Glossotherium was slightly smaller than the truly gigantic Megatherium but slightly bigger than its fellow ground sloth Megalonyx (which is famous for having been discovered by Thomas Jefferson). Glossotherium seems to have walked on its knuckles, in order to protect its large, sharp front claws, and it's famous for having turned up in the La Brea Tar Pits alongside the preserved remains of Smilodon, the Saber-Tooth Tiger, which may have been one of its natural predators.

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Glyptodon

glyptodon
Glyptodon. Pavel Riha

The giant armadillo Glyptodon was probably hunted to extinction by early humans, who prized it not only for its meat but also for its roomy carapace--there's evidence that South American settlers sheltered from the elements under Glyptodon shells! See an in-depth profile of Glyptodon

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Hapalops

hapalops
Hapalops. American Museum of Natural History

Name:

Hapalops (Greek for "gentle face"); pronounced HAP-ah-lops

Habitat:

Woodlands of South America

Historical Epoch:

Early-Middle Miocene (23-13 million years ago)

Size and Weight:

About four feet long and 50-75 pounds

Diet:

Plants

Distinguishing Characteristics:

Long, stout legs; long claws on front feet; few teeth

 

Giant mammals always have diminutive ancestors lurking somewhere far down on the family tree, a rule that applies to horses, elephants and, yes, sloths. Everyone knows about the Giant Sloth, Megatherium, but you may not have been aware that this multi-ton beast was related to the sheep-sized Hapalops, which lived tens of millions of years earlier, during the Miocene epoch. As prehistoric sloths go, Hapalops had a few odd characteristics: the long claws on its front hands probably obliged it to walk on its knuckles, like a gorilla, and it seems to have possessed a slightly bigger brain than its descendants further on down the line. The paucity of teeth in Hapalops' mouth is a clue that this mammal subsisted on soft vegetation that didn't require much robust chewing--maybe it needed a bigger brain to find its favorite meals!

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The Horned Gopher

horned gopher
The Horned Gopher. National Museum of Natural History

The Horned Gopher (genus name Ceratogaulus) lived up to its name: this foot-long, otherwise inoffensive gopher-like creature sported a pair of sharp horns on its snout, the only rodent ever known to have evolved such an elaborate head display. See an in-depth profile of the Horned Gopher

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Hyrachyus

hyrachyus
Hyrachyus (Wikimedia Commons).

Name:

Hyrachyus (Greek for "hyrax-like"); pronounced HI-rah-KAI-uss

Habitat:

Plains of North America

Historical Epoch:

Middle Eocene (40 million years ago)

Size and Weight:

About 3-5 feet long and 100-200 pounds

Diet:

Plants

Distinguishing Characteristics:

Moderate size; muscular upper lip

 

You may never have given the matter much thought, but modern-day rhinoceroses are most closely related to tapirs--pig-like ungulates with flexible, elephant-trunk-like upper lips (tapirs are famous for their cameo appearance as "prehistoric" beasts in Stanley Kubrick's movie 2001: A Space Odyssey). As far as paleontologists can tell, the 40-million-year-old Hyrachus was ancestral to both these creatures, with rhino-like teeth and the barest beginnings of a prehensile upper lip. Oddly enough, considering its descendants, this megafauna mammal was named after an entirely different (and even more obscure) modern creature, the hyrax.

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Hyracodon

hyracodon
Hyracodon. Heinrich Harder

Name:

Hyracodon (Greek for "hyrax tooth"); pronounced hi-RACK-oh-don

Habitat:

Woodlands of North America

Historical Epoch:

Middle Oligocene (30-25 million years ago)

Size and Weight:

About five feet long and 500 pounds

Diet:

Plants

Distinguishing Characteristics:

Horse-like build; three-toed feet; large head

 

Although Hyracodon looked a lot like a prehistoric horse--which were thick on the ground in Oligocene North America--an analysis of this creature's legs shows that it wasn't a particularly fast runner, and therefore probably spent most of its time in sheltered woodlands rather than open plains (where it would have been more susceptible to predation). In fact, Hyracodon is now believed to have been the earliest megafauna mammal on the evolutionary line leading to modern-day rhinoceroses (a journey that included some truly enormous intermediate forms, such as the 15-ton Indricotherium).

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Icaronycteris

icaronycteris
Icaronycteris. Wikimedia Commons

Name:

Icaronycteris (Greek for "Icarus night flyer"); pronounced ICK-ah-roe-NICK-teh-riss

Habitat:

Woodlands of North America

Historical Epoch:

Early Eocene (55-50 million years ago)

Size and Weight:

About one foot long and a few ounces

Diet:

Insects

Distinguishing Characteristics:

Small size; long tail; shrew-like teeth

 

Probably for aerodynamic reasons, prehistoric bats weren't any bigger (or any more dangerous) than modern bats. Icaronycteris is the earliest bat for which we have solid fossil evidence, and even 50 million years ago it had a full panoply of bat-like traits, including wings made of skin and a talent for echolocation (moth scales have been found in the stomach of one Icaronycteris specimen, and the only way to catch moths at night is with radar!) However, this early Eocene bat did betray some primitive characteristics, mostly involving its tail and teeth, which were relatively undifferentiated and shrew-like compared to the teeth of modern bats. (Oddly enough, Icaronycteris existed in the same time and place as another prehistoric bat that lacked the ability to echolocate, Onychonycteris.)

40
of 91

Indricotherium

indricotherium. Indricotherium (Sameer Prehistorica)

A gigantic ancestor of the modern rhinoceros, the 15-to-20-ton Indricotherium possessed a fairly long neck (though nothing approaching what you'd see on a sauropod dinosaur), as well as surprisingly thin legs capped by three-toed feet. See an in-depth profile of Indricotherium

41
of 91

Josephoartigasia

josephoartigasia
Josephoartigasia. Nobu Tamura

Name

Josephoartigasia; pronounced JOE-seff-oh-ART-ih-GAY-zha

Habitat

Plains of South America

Historical Epoch

Pliocene-Early Pleistocene (4-2 million years ago)

Size and Weight

About 10 feet long and one ton

Diet

Probably plants

Distinguishing Characteristics

Large size; blunt, hippo-like head with large front teeth

 

You think you have a mouse problem? It's a good thing you didn't live in South America a few million years ago, when the one-ton rodent Josephoartigasia prowled the continent's swamps and estuaries. (For the sake of comparison, Josephoartigasia's closest living relative, the Pacarana of Bolivia, "only" weighs about 30 to 40 pounds, and the  next-biggest prehistoric rodent, Phoberomys, was about 500 pounds lighter.) Since it's represented in the fossil record by a single skull, there's still a lot paleontologists don't know about the every life of Josephoartigasia; we can only guess at its diet, which probably consisted of soft plants (and possibly fruits), and it likely wielded its giant front teeth either to compete for females or to deter predators (or both).

42
of 91

The Killer Pig

entelodon killer pig
Entelodon (Killer Pig). Heinrich Harder

Entelodon has been immortalized as the "Killer Pig," even though, like modern pigs, it ate plants as well as meat. This Oligocene mammal was about the size of a cow, and had a noticeably pig-like face with wart-like, bone-supported wattles on its cheeks. More about the Killer Pig

43
of 91

Kretzoiarctos

kretzoiarctos
Kretzoiarctos. Nobu Tamura

Name:

Kretzoiarctos (Greek for "Kretzoi's bear"); pronounced KRET-zoy-ARK-tose

Habitat:

Woodlands of Spain

Historical Epoch:

Late Miocene (12-11 million years ago)

Size and Weight:

About four feet long and 100 pounds

Diet:

Probably omnivorous

Distinguishing Characteristics:

Moderate size; possibly panda-like fur coloring

 

A few years ago, paleontologists discovered what was then considered to be the earliest ancestor of the modern Panda Bear, Agriarctos (aka the "earth bear"). Now, further study of some Agriarctos-like fossils unearthed in Spain has led experts to designate an even earlier genus of Panda ancestor, Kretzoiarctos (after paleontologist Miklos Kretzoi). Kretzoiarctos lived about a million years before Agriarctos, and it enjoyed an omnivorous diet, feasting on the tough vegetables (and occasional small mammals) of its western European habitat. Exactly how did a hundred-pound, tuber-eating bear evolve into the much bigger, bamboo-eating Giant Panda of eastern Asia? That's a question that demands further study (and further fossil discoveries)!

44
of 91

Leptictidium

leptictidium
Leptictidium. Wikimedia Commons

When various fossils of Leptictidium were unearthed in Germany a few decades ago, paleontologists were faced with a conundrum: this small, shrew-like mammal appeared to be completely bipedal! See an in-depth profile of Leptictidium

45
of 91

Leptomeryx

leptomeryx
Leptomeryx (Nobu Tamura).

Name

Leptomeryx (Greek for "light ruminant"); pronounced LEP-toe-MEH-rix

Habitat

Plains of North America

Historical Epoch

Middle Eocene-Early Miocene (41-18 million years ago)

Size and Weight

About 3-4 feet long and 15-35 pounds

Diet

Plants

Distinguishing Characteristics

Small size; slender body

 

As common as it was on the North American plains tens of million of years ago, Leptomeryx would get more press if it were easier to classify. Outwardly, this slender artiodactyl (even-toed hooved mammal) resembled a deer, but it was technically a ruminant, and thus had more in common with modern cows. (Ruminants possess multi-segmented stomachs designed to digest tough vegetable matter, and are also constantly chewing their cud.) One interesting thing about Leptomeryx is that the later species of this megafauna mammal had a more elaborate tooth structure, which was probably an adaptation to their increasingly parched ecosystem (which encouraged the growth of tougher-to-digest plants).

46
of 91

Macrauchenia

macrauchenia
Macrauchenia. Sergio Perez

The long trunk of Macrauchenia hints that this megafauna mammal fed on the low-lying leaves of trees, but its horse-like teeth point to a diet of grass. One can only conclude that Macrauchenia was an opportunistic browser and grazer, which helps to explain its jigsaw-puzzle-like appearance. See an in-depth profile of Macrauchenia

47
of 91

Megaloceros

megaloceros
Megaloceros. Flickr

The males of Megaloceros were distinguished by their enormous, spreading, ornate antlers, which spanned almost 12 feet from tip to tip and weighed just short of 100 pounds. Presumably, this prehistoric deer had an exceptionally strong neck! See an in-depth profile of Megaloceros

48
of 91

Megalonyx

megalonyx
Megalonyx. American Museum of Natural History

Besides its one-ton bulk, Megalonyx, aso known as the Giant Ground Sloth, was distinguished by its significantly longer front than hind legs, a clue that it used its long front claws to rope in copious amounts of vegetation from trees. See an in-depth profile of Megalonyx

49
of 91

Megatherium

megatherium giant sloth
Megatherium (Giant Sloth). Paris Natural History Museum

Megatherium, aka the Giant Sloth, is an interesting case study in convergent evolution: if you ignore its thick coat of fur, this mammal was anatomically very similar to the tall, pot-bellied, razor-clawed breed of dinosaurs known as therizinosaurs. See an in-depth profile of Megatherium

50
of 91

Megistotherium

megistotherium
Megistotherium. Roman Yevseev

Name:

Megistotherium (Greek for "largest beast"); pronounced meh-JISS-toe-THEE-ree-um

Habitat:

Plains of north Africa

Historical Epoch:

Early Miocene (20 million years ago)

Size and Weight:

About 12 feet long and 1,000-2,000 pounds

Diet:

Meat

Distinguishing Characteristics:

Large size; elongated skull with powerful jaws

 

You can get the true measure of Megistotherium by learning its last, i.e., species name: "osteophlastes," Greek for "bone-crushing." This was the biggest of all the creodonts, the carnivorous mammals that preceded modern wolves, cats and hyenas, weighing close to a ton and with a long, massive, powerfully jawed head. As big as it was, though, it's possible that Megistotherium was unusually slow and clumsy, a hint that it may have scavenged already-dead carcasses (like a hyena) rather than actively hunting down prey (like a wolf). The only megafauna carnivore to rival it in size was Andrewsarchus, which may or may not have been substantially bigger, depending on whose reconstruction you believe!

51
of 91

Menoceras

menoceras
Menoceras (Wikimedia Commons).

Name:

Menoceras (Greek for "crescent horn"); pronounced meh-NOSS-seh-ross

Habitat:

Plains of North America

Historical Epoch:

Early-Middle Miocene (30-20 million years ago)

Size and Weight:

About 4-5 feet long and 300-500 pounds

Diet:

Plants

Distinguishing Characteristics:

Small size; horns on males

 

As prehistoric rhinoceroses go, Menoceras didn't cut an especially impressive profile, especially compared to such gigantic, weirdly proportioned members of the breed as the 20-ton Indricotherium (which appeared on the scene much later). The true importance of the slender, boar-sized Menoceras is that it was the first ancient rhino to evolve horns, a small pair on the snouts of males (a sure sign that these horns were a sexually selected characteristic, and not meant as a form of defense). The discovery of numerous Menoceras bones in various places in the United States (including Nebraska, Florida, California and New Jersey) is evidence that this megafauna mammal roamed the American plains in wide-ranging herds.

52
of 91

Merycoidodon

merycoidodon
Merycoidodon (Wikimedia Commons).

Name:

Merycoidodon (Greek for "ruminant-like teeth"); pronounced MEH-rih-COY-doe-don

Habitat:

Plains of North America

Historical Epoch:

Oligocene (33-23 million years ago)

Size and Weight:

About five feet long and 200-300 pounds

Diet:

Plants

Distinguishing Characteristics:

Short legs; horse-like head with primitive teeth

 

Merycoidodon is one of those prehistoric herbivores that's hard to get a good grasp on, since it doesn't have any analogous counterparts alive today. This megafauna mammal is technically classified as a "tylopod," a subfamily of artiodactyls (even-toed ungulates) related to both pigs and cattle, and today represented only by modern camels. However you choose to classify it, Merycoidodon was one of the most successful grazing mammals of the Oligocene epoch, represented as it is by thousands of fossils (an indication that Merycoidodon roamed the North American plains in vast herds).

53
of 91

Mesonyx

mesonyx
Mesonyx. Charles R. Knight

Name:

Mesonyx (Greek for "middle claw"); pronounced MAY-so-nix

Habitat:

Plains of North America

Historical Epoch:

Early-Middle Eocene (55-45 million years ago)

Size and Weight:

About five feet long and 50-75 pounds

Diet:

Meat

Distinguishing Characteristics:

Wolf-like appearance; narrow snout with sharp teeth

 

If you saw a picture of Mesonyx, you might be forgiven for thinking that it was ancestral to modern wolves and dogs: this Eocene mammal had a slender, quadrupedal build, with canine-like paws and a narrow snout (probably tipped by a wet, black nose). However, Mesonyx appeared way too early in evolutionary history to be directly related to dogs; rather, paleontologists speculate that it may have lain near the root of the evolutionary branch that led to whales (note its similarity to the land-dwelling whale ancestor Pakicetus). Mesonyx also played an important part in the discovery of another, bigger Eocene carnivore, the gigantic Andrewsarchus; this central Asian megafauna predator was reconstructed from a single, partial skull based on its presumed relationship to Mesonyx.

54
of 91

Metamynodon

metamynodon
Metamynodon. Heinrich Harder

Name:

Metamynodon (Greek for "beyond Mynodon"); pronounced META-ah-MINE-oh-don

Habitat:

Swamps and rivers of North America

Historical Epoch:

Late Eocene-Early Oligocene (35-30 million years ago)

Size and Weight:

About 13 feet long and 2-3 tons

Diet:

Plants

Distinguishing Characteristics:

Large size; high-set eyes; four-toed front feet

 

If you've never quite understood the difference between rhinoceroses and hippopotamuses, you're bound to be confused by Metamynodon, which was technically a prehistoric rhinoceros but looked much, much more like an ancient hippo. In a classic example of convergent evolution—the tendency for creatures that occupy the same ecosystems to evolve the same traits and behaviors—Metamynodon possessed a bulbous, hippo-like body and high-set eyes (the better for scanning its surroundings while it was submerged in water), and lacked the horn characteristic of modern rhinos. Its immediate successor was the Miocene Teleoceras, which also looked like a hippo but at least possessed the smallest hint of a nasal horn.

55
of 91

Metridiochoerus

metridiochoerus
The lower jaw of Metridiochoerus. Wikimedia Commons

Name

Metridiochoerus (Greek for "frightful pig"); pronounced meh-TRID-ee-oh-CARE-us

Habitat

Plains of Africa

Historical Epoch

Late Pliocene-Pleistocene (3 million-one million years ago)

Size and Weight

About five feet long and 200 pounds

Diet

Probably omnivorous

Distinguishing Characteristics

Moderate size; four tusks in upper jaw

 

Although its name is Greek for "frightful pig," and it's sometimes called the Giant Warthog, Metridiocheorus was a true runt among the multi-ton mammalian megafauna of Pleistocene Africa. The fact is that, at 200 pounds or so, this prehistoric porker was only slightly bigger than the still-extant African Warthog, albeit equipped with more dangerous-looking tusks. The fact that the African Warthog survived into the modern age, while the Giant Warthog went extinct, may have had something to with the latter's inability to survive times of scarcity (after all, a smaller mammal can endure famine for longer stretches than a larger one).

56
of 91

Moropus

moropus
Moropus. National Museum of Natural History

Name:

Moropus (Greek for "stupid foot"); pronounced MORE-oh-pus

Habitat:

Plains of North America

Historical Epoch:

Early-Middle Miocene (23-15 million years ago)

Size and Weight:

About 10 feet long and 1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Horse-like snout; three-toed front feet; longer front than hind limbs

 

Although the name Moropus ("stupid foot") is striking in translation, this prehistoric mammal might have been better served by its original moniker, Macrotherium ("giant beast")--which would at least drive home its relationship to the other "-therium" megafauna of the Miocene epoch, especially its close relative Chalicotherium. Essentially, Moroopus was a slightly bigger version of Chalicotherium, both of these mammals characterized by their long front legs, horse-like snouts and herbivorous diets. Unlike Chalicotherium, though, Moropus seems to have walked "properly" on its three-clawed front feet, rather than on its knuckles, like a gorilla.

57
of 91

Mylodon

mylodon
Mylodon (Wikimedia Commons).

Name:

Mylodon (Greek for "peaceful tooth"); pronounced MY-low-don

Habitat:

Plains of South America

Historical Epoch:

Pleistocene-Modern (2 million-10,000 years ago)

Size and Weight:

About 10 feet long and 500 pounds

Diet:

Plants

Distinguishing Characteristics:

Relatively small size; thick hide; sharp claws

 

Compared to its fellow giant sloths like the three-ton Megatherium and Eremotherium, Mylodon was the runt of the litter, "only" measuring about 10 feet from head to tail and weighing about 500 pounds. Perhaps because it was relatively small, and thus a more likely target for predators, this prehistoric megafauna mammal had an unusually tough pelt reinforced by tough "osteoderms," and it was also equipped with sharp claws (which probably weren't used for defense, but to root out tough vegetable matter). Interestingly, the scattered pelt and dung fragments of Mylodon have been so well preserved that paleontologists once believed this prehistoric sloth never went extinct, and was still living in the wilds of South America (a premise that was soon proven incorrect).

58
of 91

Nesodon

nesodon
Nesodon. Charles R. Knight

Name:

Nesodon (Greek for "island tooth"); pronounced NAY-so-don

Habitat:

Woodlands of South America

Historical Epoch:

Late Oligocene-Middle Miocene (29-16 million years ago)

Size and Weight:

About 5 to 10 feet long and 200 to 1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Large head; stocky trunk

 

Named in the mid-19th century by the famous paleontologist Richard Owen, Nesodon was only assigned as a "toxodont"—and thus a close relative of the better-known Toxodon—in 1988. Somewhat confusingly, this South American megafauna mammal comprised three separate species, ranging from sheep-sized to rhinoceros-sized, all of them looking vaguely like a cross between a rhino and a hippopotamus. Like its closest relatives, Nesodon is technically categorized as a "notoungulate," a distinctive breed of hooved mammals that have left no direct living descendants.

59
of 91

Nuralagus

nuralagus
Nuralagus. Nobu Tamura

The Pliocene rabbit Nuralagus weighed over five times as much as any species of rabbit or hare living today; the single fossil specimen points to an individual of at least 25 pounds! See an in-depth profile of Nuralagus

60
of 91

Obdurodon

obdurodon
Obdurodon. Australian Museum

The ancient monotreme Obdurodon was about the same size as its modern playtpus relatives, but its bill was comparably broad and flat and (here's the main difference) studded with teeth, which adult platypuses lack. See an in-depth profile of Obdurodon

61
of 91

Onychonycteris

onychonycteris
Onychonycteris. Wikimedia Commons

Name:

Onychonycteris (Greek for "clawed bat"); pronounced OH-nick-oh-NICK-teh-riss

Habitat:

Woodlands of North America

Historical Period:

Early Eocene (55-50 million years ago)

Size and Weight:

A few inches long and a few ounces

Diet:

Insects

Distinguishing Characteristics:

Five-clawed hands; primitive inner ear structure

 

Onychonycteris, the "clawed bat," is a case study in the unexpected twists and turns of evolution: this prehistoric bat existed alongside Icaronycteris, another flying mammal of early Eocene North America, yet it differed from its winged relative in several important respects. Whereas the inner ears of Icaronycteris show the beginnings of "echolating" structures (meaning this bat must have been capable of night hunting), the ears of Onychonycteris were much more primitive. Assuming that Onychonycteris has precedence in the fossil record, this would mean that the earliest bats developed the ability to fly before they developed the ability to echolocate, though not all paleontologists are convinced.

62
of 91

Palaeocastor

palaeocastor
Palaeocastor. Nobu Tamura

Name:

Palaeocastor (Greek for "ancient beaver"); pronounced PAL-ay-oh-cass-tore

Habitat:

Woodlands of North America

Historical Epoch:

Late Oligocene (25 million years ago)

Size and Weight:

About one foot long and a few pounds

Diet:

Plants

Distinguishing Characteristics:

Small size; strong front teeth

 

The 200-pound Castoroides may be the best-known prehistoric beaver, but if was far from the first: that honor probably belongs to the much smaller Palaeocastor, a foot-long rodent that eschewed elaborate dams for even more elaborate, eight-foot-deep burrows. Oddly enough, the preserved remnants of these burrows—narrow, twisty holes known in the American west as "Devil's Corkscrews"—were discovered long before Palaeocastor itself, and it took some convincing on the part of scientists before people accepted that a creature as small as Palaeocastor could be so industrious. Even more impressively, Palaeocastor seems to have dug out its burrows not with its hands, like a mole, but with its oversized front teeth!

63
of 91

Palaeochiropteryx

palaeochiropteryx
Palaeochiropteryx. Wikimedia Commons

Name:

Palaeochiropteryx (Greek for "ancient hand wing"); pronounced PAL-ay-oh-kih-ROP-teh-rix

Habitat:

Woodlands of western Europe

Historical Epoch:

Early Eocene (50 million years ago)

Size and Weight:

About three inches long and one ounce

Diet:

Insects

Distinguishing Characteristics:

Primitive wings; distinctive inner-ear structure

 

At some point during the early Eocene epoch--and probably well before, as far back as the late Cretaceous period--the first mouse-sized mammals evolved the ability to fly, inaugurating the evolutionary line leading to modern bats. The tiny (no more than three inches long and one ounce) Palaeochiropteryx already possessed the beginnings of the bat-like inner-ear structure necessary for echolocation, and its stubby wings would have allowed it to flutter at low altitudes over the forest floors of western Europe. Not surprisingly, Palaeochiropteryx seems to have been closely related to its North American contemporary, the early Eocene Icaronycteris.

64
of 91

Palaeolagus

palaeolagus
Palaeolagus. Wikimedia Commons

Name:

Palaeolagus (Greek for "ancient rabbit"); pronounced PAL-ay-OLL-ah-gus

Habitat:

Plains and woodlands of North America

Historical Epoch:

Oligocene (33-23 million years ago)

Size and Weight:

About one foot long and a few pounds

Diet:

Grass

Distinguishing Characteristics:

Short feet; long tail; rabbit-like build

 

Disappointingly, the ancient rabbit Palaeolagus wasn't monster-sized, like so many prehistoric ancestors of existing mammals (for sake of contrast, witness the Giant Beaver, Castoroides, which weighed as much as a full-grown human). Except for its slightly shorter hind feet (a clue that it didn't hop like modern rabbits), two pairs of upper incisors (compared to one for modern rabbits) and slightly longer tail, Palaeolagus looked remarkably like its modern descendants, complete with long bunny ears. Very few complete fossils of Palaeolagus have been found; as you might imagine, this tiny mammal was so often preyed on by Oligocene carnivores that it has survived down to the present day only in bits and pieces.

65
of 91

Paleoparadoxia

paleoparadoxia
Paleoparadoxia (Wikimedia Commons).

Name:

Paleoparadoxia (Greek for "ancient puzzle"); pronounced PAL-ee-oh-PAH-ra-DOCK-see-ah

Habitat:

Shorelines of the northern Pacific

Historical Epoch:

Miocene (20-10 million years ago)

Size and Weight:

About 10 feet long and 1,000-2,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Short, inward-curving legs; bulky body; horse-like head

 

Like its close relative, Desmostylus, Paleoparadoxia represented an obscure offshoot of semi-aquatic mammals that died off about 10 million years ago and left no living descendants (though they may be distantly related to dugongs and manatees). Named by a bemused paleontologist after its odd mix of features, Paleoparadoxia (Greek for "ancient puzzle") had a large, horse-like head, a squat, walrus-like trunk, and splayed, inward-curving legs more reminiscent of a prehistoric crocodile than a megafauna mammal. Two complete skeletons of this creature are known, one from the Pacific coast of North America and another from Japan.

66
of 91

Pelorovis

pelorovis
Pelorovis (Wikimedia Commons).

Name:

Pelorovis (Greek for "monstrous sheep"); pronounced PELL-oh-ROVE-iss

Habitat:

Plains of Africa

Historical Epoch:

Pleistocene-Modern (2 million-5,000 years ago)

Size and Weight:

About 10 feet long and one ton

Diet:

Grass

Distinguishing Characteristics:

Large size; large, upward-curving horns

 

Despite its fanciful name—which is Greek for "monstrous sheep"—Pelorovis wasn't a sheep at all, but a gigantic artiodactyl (even-toed ungulate) closely related to the modern water buffalo. This central African mammal looked like a gigantic bull, the most notable difference being the huge (about six feet long from base to tip), paired horns on top of its massive head. As you might expect for a tasty bit of mammalian megafauna that shared the African plains with early humans, specimens of Pelorovis have been found bearing the imprints of primitive stone weapons.

67
of 91

Peltephilus

peltephilus
Peltephilus. Getty Images

Name:

Peltephilus (Greek for "armor lover"); pronounced PELL-teh-FIE-luss

Habitat:

Plains of South America

Historical Epoch:

Late Oligocene-Early Miocene (25-20 million years ago)

Size and Weight:

About five feet long and 150-200 pounds

Diet:

Unknown; possibly omnivorous

Distinguishing Characteristics:

Armor plating along back; two horns on snout

 

One of the more comical-looking megafauna mammals of prehistoric times, Peltephilus looked like a giant badger pretending to be a cross between an Ankylosaurus and a rhinoceros. This five-foot-long armadillo sported some impressive-looking, flexible armor (which would have allowed it to curl up into a big ball when threatened), as well as two largish horns on its snout, which were undoubtedly a sexually selected characteristic (i.e., Peltephilus males with bigger horns got to mate with more females). As big as it was, though, Peltephilus was no match for giant armadillo descendants like Glyptodon and Doedicurus that succeeded it by a few million years.

68
of 91

Phenacodus

phenacodus
Phenacodus. Heinrich Harder

Name:

Phenacodus (Greek for "obvious teeth"); pronounced fee-NACK-oh-duss

Habitat:

Plains of North America

Historical Epoch:

Early-Middle Eocene (55-45 million years ago)

Size and Weight:

About five feet long and 50-75 pounds

Diet:

Grass

Distinguishing Characteristics:

Long, straight legs; long tail; narrow snout

 

Phenacodus was one of the "plain vanilla" mammals of the early Eocene epoch, a medium-sized, vaguely deer- or horse-like herbivore that evolved a mere 10 million years after the dinosaurs had gone extinct. Its importance lies in the fact that it seems to have occupied the root of the ungulate family tree; Phenaocodus (or a close relative) may have been the hoofed mammal from which later perissodactyls (odd-toed ungulates) and artiodactyls (even-toed ungulates) both evolved. This creature's name, Greek for "obvious teeth," derives from its, well, obvious teeth, which were well-suited to grinding up the tough vegetation of its North American habitat.

69
of 91

Platygonus

platygonus
Platygonus (Wikimedia Commons).

Name:

Platygonus; pronounced PLATT-ee-GO-nuss

Habitat:

Plains of North America

Historical Epoch:

Late Miocene-Modern (10 million-10,000 years ago)

Size and Weight:

About three feet long and 100 pounds

Diet:

Plants

Distinguishing Characteristics:

Long legs; pig-like snout

 

Peccaries are vicious, omnivorous, pig-like herd animals that live mostly in South and Central America; Platygonus was one of their oldest ancestors, a relatively long-legged member of the breed that may occasionally have ventured beyond the forests of its North American habitat and onto the open plains. Unlike modern peccaries, Platygonus seems to have been a strict herbivore, using its dangerous-looking tusks only to intimidate predators or other members of the herd (and possibly to help it dig up tasty vegetables). This megafauna mammal also had an unusually advanced digestive system similar to that of ruminants (i.e., cows, goats and sheep).

70
of 91

Poebrotherium

poebrotherium
Poebrotherium. Wikimedia Commons

Name:

Poebrotherium (Greek for "grass-eating beast"); pronounced POE-ee-bro-THEE-ree-um

Habitat:

Plains of North America

Historical Epoch:

Oligocene (33-23 million years ago)

Size and Weight:

About three feet tall and 75-100 pounds

Diet:

Plants

Distinguishing Characteristics:

Small size; llama-like head

 

It's a little-known fact that the first camels evolved in North America--and that these pioneering ruminants (i.e., cud-chewing mammals) only later spread to northern Africa and the Middle East, where most modern camels are found today. Named in the middle 19th century by the famous paleontologist Joseph Leidy, Poebrotherium is one of the earliest camels yet identified in the fossil record, a long-legged, sheep-sized herbivore with a distinctly llama-like head. At this stage in camel evolution, about 35 to 25 million years ago, characteristic features like fatty humps and knobby legs had yet to appear; in fact, if you didn't know Poebrotherium was a camel, you might assume this megafauna mammal was a prehistoric deer.

71
of 91

Potamotherium

potamotherium
Potamotherium. Nobu Tamura

Name:

Potamotherium (Greek for "river beast"); pronounced POT-ah-moe-THEE-ree-um

Habitat:

Rivers of Europe and North America

Historical Epoch:

Miocene (23-5 million years ago)

Size and Weight:

About five feet long and 20-30 pounds

Diet:

Fish

Distinguishing Characteristics:

Slender body; short legs

 

When its fossils were first discovered, way back in 1833, no one was quite sure what to make of Potamotherium, though the preponderance of the evidence pointed to its being a prehistoric weasel (a logical conclusion, given this megafauna mammal's sleek, weasel-like body). However, further studies have relocated Potamotherium on the evolutionary tree as a distant ancestor of modern pinnipeds, a family of marine mammals that includes seals and walruses. The recent discovery of Puijila, the "walking seal," has sealed the deal, so to speak: these two mammals of the Miocene epoch were clearly closely related to each other.

72
of 91

Protoceras

protoceras
Protoceras. Heinrich Harder

Name:

Protoceras (Greek for "first horn"); pronounced PRO-toe-SEH-rass

Habitat:

Plains of North America

Historical Epoch:

Late Oligocene-Early Miocene (25-20 million years ago)

Size and Weight:

About 3-4 feet long and 100-200 pounds

Diet:

Plants

Distinguishing Characteristics:

Four-toed feet; three pairs of short horns on head

 

If you came across Protoceras and its "protoceratid" relatives 20 million years ago, you might be forgiven for thinking that these megafauna mammals were prehistoric deer. Like so many ancient artiodactyls (even-toed ungulates), though, Protoceras and its ilk have proven difficult to classify; their closest living relatives are most likely camels rather than elks or pronghorns. Whatever its classification, Protoceras was one of the earliest members of this distinctive group of megafauna mammals, with four-toed feet (later protoceratids only had two toes) and, on the males, three sets of paired, stubby horns running from the top of the head down to the snout.

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Puijila

puijila
Puijila (Wikimedia Commons).

The 25-million-year-old Puijila didn't look much like the ultimate ancestor of modern seals, sea lions and walruses--in the same way that "walking whales" like Ambulocetus didn't much resemble their giant marine descendants. See an in-depth profile of Puijila

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Pyrotherium

pyrotherium
Pyrotherium. Flickr

Name:

Pyrotherium (Greek for "fire beast"); pronounced PIE-roe-THEE-ree-um

Habitat:

Woodlands of South America

Historical Epoch:

Early Oligocene (34-30 million years ago)

Size and Weight:

About 10 feet long and 500-1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Long, narrow skull; tusks; elephant-like trunk

 

You'd think a dramatic name like Pyrotherium—Greek for "fire beast"—would be bestowed on a dragon-like prehistoric reptile, but no such luck. Pyrotherium was actually a medium-sized, vaguely elephant-like megafauna mammal that prowled the woodlands of South America about 30 million years ago, its tusks and prehensile snout pointing to a classic pattern of convergent evolution (in other words, Pyrotherium lived like an elephant, so it evolved to look like an elephant as well). Why "fire beast?" This is because this herbivore's remains were discovered in beds of ancient volcanic ash. 

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Samotherium

samotherium
Samotherium. Wikimedia Commons

Name:

Samotherium (Greek for "Samos beast"); pronounced SAY-moe-THEE-ree-um

Habitat:

Plains of Eurasia and Africa

Historical Epoch:

Late Miocene-Early Pliocene (10-5 million years ago)

Size and Weight:

About 10 feet tall and half a ton

Diet:

Plants

Distinguishing Characteristics:

Short neck; two ossicones on head

 

You can tell just by looking at it that Samotherium enjoyed a lifestyle very different from that of modern giraffes: This megafauna mammal possessed a relatively short neck and a cow-like muzzle, indicating that it grazed on the low-lying grass of late Miocene Africa and Eurasia rather than nibbling the high leaves of trees. Still, there's no mistaking Samotherium's kinship with modern giraffes, as evidenced by the pair of ossicones (horn-like protuberances) on its head and its long, slender legs.

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Sarkastodon

sarkastodon
Sarkastodon. Dmitri Bogdanov

Name:

Sarkastodon (Greek for "flesh-tearing tooth"); pronounced sar-CASS-toe-don

Habitat:

Plains of central Asia

Historical Epoch:

Late Eocene (35 million years ago)

Size and Weight:

About 10 feet long and 500-1,000 pounds

Diet:

Meat

Distinguishing Characteristics:

Bear-like build; long, fluffy tail

 

Once you get past its name--which has nothing to do with the word "sarcastic"--Sarkastodon looms in importance as a large creodont of the late Eocene epoch (the creodonts were a prehistoric group of carnivorous megafauna mammals that preceded modern wolves, hyenas and big cats). In a typical example of convergent evolution, Sarkastodon looked a lot like a modern grizzly bear (if you make allowances for its long, fluffy tail), and it probably lived a lot like a grizzly bear as well, feeding opportunistically on fish, plants and other animals. Also, Sarkastodon's large, heavy teeth were especially well adapted to cracking bones, either of live prey or already-dead carcasses.

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The Shrub-Ox

shrub ox
The Shrub-Ox (Robert Bruce Horsfall).

Name

Shrub-Ox; genus name Euceratherium (pronounced YOU-see-rah-THEE-ree-um)

Habitat

Plains of North America

Historical Epoch

Pleistocene-Modern (2 million-10,000 years ago)

Size and Weight

About six feet long and 1,000-2,000 pounds

Diet

Trees and shrubs

Distinguishing Characteristics

Long horns; shaggy coat of fur

 

A true bovid--the family of cloven-hoofed ruminants whose modern members include cows, gazelles and impalas--the Shrub-Ox was notable for grazing not on grass, but on low-lying trees and shrubs (paleontologists can determine this by examining this megafauna mammal's coprolites, or fossilized poop). Oddly enough, the Shrub-Ox inhabited North America for tens of thousands of years before the arrival of the continent's most famous bovid, the American Bison, which migrated from Eurasia via the Bering land bridge. Like other megafauna mammals in its general size range, Euceratherium went extinct shortly after the last Ice Age, about 10,000 years ago.

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Sinonyx

sinonyx
Sinonyx (Wikimedia Commons).

Name:

Sinonyx (Greek for "Chinese claw"); pronounced sie-NON-nix

Habitat:

Plains of eastern Asia

Historical Epoch:

Late Paleocene (60-55 million years ago)

Size and Weight:

About five feet long and 100 pounds

Diet:

Meat

Distinguishing Characteristics:

Moderate size; large, long head; hooves on feet

 

Although it looked--and behaved--uncannily like a prehistoric dog, Sinonyx actually belonged to a family of carnivorous mammals, the mesonychids, that went extinct about 35 million years ago (other famous mesonychids included Mesonyx and the gigantic, one-ton Andrewsarchus, the largest terrestrial mammalian predator that ever lived). The moderately sized, tiny-brained Sinonyx prowled the plains and seashores of late Paleocene Asia a mere 10 million years after the dinosaurs went extinct, an example of how quickly the tiny mammals of the Mesozoic Era evolved during the ensuing Cenozoic to occupy vacant ecological niches.

One thing that set Sinonyx apart from the true prehistoric ancestors of dogs and wolves (which arrived on the scene millions of years later) is that it possessed small hooves on its feet, and was ancestral not to modern mammalian carnivores, but to even-toed ungulates like deer, sheep and giraffes. Until recently, paleontologists even speculated that Sinonyx may even have been ancestral to the first prehistoric whales (and thus a close relative of early cetacean genera like Pakicetus and Ambulocetus), though it now seems that mesonychids were distant cousins to the whales, a few times removed, rather than their direct progenitors.

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Sivatherium

sivatherium
Sivatherium. Heinrich Harder

Like many megafauna mammals of the Pleistocene epoch, Sivatherium was hunted to extinction by early humans; crude pictures of this prehistoric giraffe have been found preserved on rocks in the Saharan Desert, dating to tens of thousands of years ago. See an in-depth profile of Sivatherium

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The Stag Moose

stag moose
Stag Moose. Wikimedia Commons

Like other Pleistocene mammals of North America, the Stag Moose may have been hunted to extinction by early humans, but it also may have succumbed to climate change at the end of the last Ice Age and the loss of its natural pasture. See an in-depth profile of the Stag Moose

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Steller's Sea Cow

steller's sea cow
Steller's Sea Cow (Wikimedia Commons).

In 1741, a population of a thousand giant sea cows was studied by the early naturalist Georg Wilhelm Steller, who remarked on this megafauna mammal's tame disposition, undersized head on an oversized body, and exclusive diet of seaweed. See an in-depth profile of Steller's Sea Cow

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Stephanorhinus

stephanorhinus
The skull of Stephanorhinus. Wikimedia Commons

The remains of the prehistoric rhinoceros Stephanorhinus have been found in a startling number of countries, ranging from France, Spain, Russia, Greece, China, and Korea to (possibly) Israel and Lebanon. See an in-depth profile of Stephanorhinus

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Syndyoceras

syndyoceras
Syndyoceras (Wikimedia Commons).

Name:

Syndyoceras (Greek for "together horn"); pronounced SIN-dee-OSS-eh-russ

Habitat:

Plains of North America

Historical Epoch:

Late Oligocene-Early Miocene (25-20 million years ago)

Size and Weight:

About five feet long and 200-300 pounds

Diet:

Plants

Distinguishing Characteristics:

Squat body; two sets of horns

 

Although it looked (and probably behaved) like a modern deer, Syndyoceras was only a remote relative: true, this megafauna mammal was an artiodactyl (even-toed ungulate), but it belonged to an obscure sub-family of this breed, the protoceratids, the only living descendants of which are camels. Syndyoceras males boasted some unusual head ornamentation: a pair of large, sharp, cattle-like horns behind the eyes, and a smaller pair, in the shape of a V, on top of the snout. (These horns also existed on females, but in drastically reduced proportions.) One distinctly un-deer-like characteristic of Syndyoceras was its large, tusk-like canine teeth, which it probably used while rooting for vegetation.

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Synthetoceras

synthetoceras
Synthetoceras. Wikimedia Commons

Name:

Synthetoceras (Greek for "combined horn"); pronounced SIN-theh-toe-SEH-rass

Habitat:

Plains of North America

Historical Epoch:

Late Miocene (10-5 million years ago)

Size and Weight:

About seven feet long and 500-750 pounds

Diet:

Plants

Distinguishing Characteristics:

Large size; elongated horn on narrow snout

 

Synthetoceras was the latest, and largest, member of the obscure family of artiodactyls (even-toed ungulates) known as protoceratids; it lived a few million years after Protoceras and Syndyoceras and was at least double their size. The males of this deer-like animal (which was actually more closely related to modern camels) boasted one of nature's most improbable head ornaments, a single, foot-long horn that branched off on the end into a small V shape (this was in addition to a more normal-looking pair of horns behind the eyes). Like modern deer, Synthetoceras seems to have lived in large herds, where the males maintained dominance (and competed for females) according to the size and impressiveness of their horns.

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Teleoceras

teleoceras
Teleoceras. Heinrich Harder

Name:

Teleoceras (Greek for "long, horned one"); pronounced TELL-ee-OSS-eh-russ

Habitat:

Plains of North America

Historical Epoch:

Late Miocene (5 million years ago)

Size and Weight:

About 13 feet long and 2-3 tons

Diet:

Plants

Distinguishing Characteristics:

Long, hippo-like trunk; small horn on snout

 

One of the best-known megafauna mammals of Miocene North America, hundreds of Teleoceras fossils have been unearthed at Nebraska's Ashfall Fossil Beds, otherwise known as "Rhino Pompeii." Teleoceras was technically a prehistoric rhinoceros, albeit one with distinctively hippo-like characteristics: its long, squat body and stumpy legs were well-adapted to a partially aquatic lifestyle, and it even had hippo-like teeth. However, the small, almost insignificant horn on the front of Teleoceras' snout points to its true rhinoceros roots. (The immediate predecessor of Teleoceras, Metamynodon, was even more hippo-like, spending most of its time in the water.)

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Thalassocnus

thalassocnus
Thalassocnus. Wikimedia Commons

Name:

Thalassocnus (Greek for "sea sloth"); pronounced THA-la-SOCK-nuss

Habitat:

Shorelines of South America

Historical Epoch:

Late Miocene-Pliocene (10-2 million years ago)

Size and Weight:

About six feet long and 300-500 pounds

Diet:

Aquatic plants

Distinguishing Characteristics:

Long front claws; downward-curving snout

 

When most people think of prehistoric sloths, they picture huge, land-dwelling beasts like Megatherium (the Giant Sloth) and Megalonyx (the Giant Ground Sloth). But the Pliocene epoch also witnessed its share of weirdly adapted, "one-off" sloths, the prime example being Thalassocnus, which dived for food off the coast of northwestern South America (the interior of that part of the continent consisting mostly of desert). Thalassocnus used its long, claw-tipped hands both to reap underwater plants and anchor itself to the sea floor while it fed, and its downward-curving head may have been tipped by a slightly prehensile snout, like that of a modern dugong.

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Titanotylopus

titanotylopus
Titanotylopus. Carl Buell

Name:

Titanotylopus (Greek for "giant knobbed foot"); pronounced tie-TAN-oh-TIE-low-pus

Habitat:

Plains of North America and Eurasia

Historical Epoch:

Pleistocene (3 million-300,000 years ago)

Size and Weight:

About 13 feet long and 1,000-2,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Large size; long, slender legs; single hump

 

The name Titanotylopus has precedence among paleontologists, but the now-discarded Gigantocamelus makes more sense: essentially, Titanotylopus was the "dino-camel" of the Pleistocene epoch, and was one of the biggest megafauna mammals of North America and Eurasia (yes, camels were once indigenous to North America!) Befitting the "dino" part of its nickname, Titanotylopus had an unusually small brain for its size, and its upper canines were larger than those of modern camels (but still not anything approaching saber-tooth status). This one-ton mammal also had broad, flat feet well-adapted to walking on rough terrain, hence the translation of its Greek name, "giant knobbed foot."

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Toxodon

toxodon
Toxodon. Wikimedia Commons

Name:

Toxodon (Greek for "bow tooth"); pronounced TOX-oh-don

Habitat:

Plains of South America

Historical Epoch:

Pleistocene-Modern (3 million-10,000 years ago)

Size and Weight:

About nine feet long and 1,000 pounds

Diet:

Grass

Distinguishing Characteristics:

Short legs and neck; large head; short, flexible trunk

 

Toxodon was what paleontologists call a "notoungulate," a megafauna mammal closely related to the ungulates (hoofed mammals) of the Pliocene and Pleistocene epochs but not quite in the same ballpark. Thanks to the wonders of convergent evolution, this herbivore evolved to look very much like a modern rhinoceros, with stubby legs, a short neck, and teeth well adapted to eating tough grass (it may also have been equipped with a short, elephant-like proboscis at the end of its snout). Many Toxodon remains have been found in close proximity to primitive arrowheads, a sure sign that this slow, lumbering beast was hunted to extinction by early humans.

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Trigonias

trigonias
Trigonias. Wikimedia Commons

Name:

Trigonias (Greek for "three-pointed jaw"); pronounced try-GO-nee-uss

Habitat:

Plains of North America and western Europe

Historical Epoch:

Late Eocene-Early Oligocene (35-30 million years ago)

Size and Weight:

About eight feet long and 1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Five-toed feet; lack of nasal horn

 

Some prehistoric rhinoceroses looked more like their modern counterparts than others: whereas you might have a hard time locating Indricotherium or Metamynodon on the rhino family tree, the same difficulty doesn't apply to Trigonias, which (if you glanced at this megafauna mammal without your glasses on) would have cut a very rhino-like profile. The difference is that Trigonias had five toes on its feet, rather than three as in most other prehistoric rhinos, and it lacked even the barest hint of a nasal horn. Trigonias lived in North America and western Europe, the ancestral home of rhinos before they relocated farther east after the Miocene epoch.

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Uintatherium

uintatherium
Uintatherium (Wikimedia Commons).

Uintatherium didn't excel in the intelligence department, with its unusually small brain compared to the rest of its bulky body. How this megafauna mammal managed to survive for so long, until it vanished without a trace about 40 million years ago, is a bit of a mystery. See an in-depth profile of Uintatherium

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The Woolly Rhino

woolly rhino
The Woolly Rhino. Mauricio Anton

Coelodonta, aka the Woolly Rhino, was very similar to modern rhinoceroses--that is, if you overlook its shaggy coat of fur and its odd, paired horns, including a big, upward-curving one on the tip of its snout and a smaller pair set further up, nearer its eyes. See an in-depth profile of the Woolly Rhino