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Prehistoric Mammals A to Z

Profiles of prehistoric mammals, including the first mammals that coexisted with the dinosaurs, prehistoric elephants, prehistoric whales, prehistoric horses, saber-toothed cats, prehistoric dogs, and the giant mammals of the Cenozoic Era. (See also the 10 Deadliest Prehistoric Mammals.)

Acrophoca
This prehistoric seal had an unusually long neck.

Acrophyseter
A long-snouted ancestor of the sperm whale.

Adelobasileus
This mammal wasn't far removed from its therapsid ancestors.

Aegyptocetus
This "Egyptian whale" spent part of its time on land.

Aelurodon
This "cat-toothed" dog behaved more like a hyena.

Aepycamelus
A giraffe-like camel of the Miocene epoch.

Aetiocetus
This primitive whale used both teeth and plankton-filtering baleen.

Afropithecus
This African primate was discovered by Richard and Mary Leakey.

Agriarctos
This ancestor of the Giant Panda lived over 10 million years ago.

Agriotherium
One of the few prehistoric bears to have lived in Africa.

Alphadon
An early marsupial of the late Cretaceous.

Ambulocetus
This "walking whale" led an otter-like lifestyle.

Amebelodon
This "shovel-toothed" elephant thrived in flooded lowlands.

American Cheetah (Miracinonyx)
It may actually have been a kind of puma.

American Lion (Panthera Leo Atrox)
The biggest lion ever to walk the earth.

American Zebra
Also known as the "Hagerman horse."

Amphicyon
Otherwise known as the "Bear Dog."

Anancus
This early elephant's tusks were as long as its entire body.

Anchitherium
A long-lived "side branch" on the equine tree of life.

Ancylotherium
This large herbivore lived alongside our human ancestors.

Andrewsarchus
The biggest terrestrial meat-eating mammal that ever lived.

Archaeoindris
A gorilla-sized lemur from Madagascar.

Archaeolemur
This ancient lemur only went extinct 1,000 years ago.

Archicebus
Was this tiny, mouse-like mammal the first true primate?

Ardipithecus
This early hominid was unusually mild-tempered.

Arsinoitherium
A two-horned, rhino-like browser from Africa.

Astrapotherium
An elephant-like ungulate from South America.

Atlas Bear
Africa's only indigenous bear.

Auroch
This giant bovine went extinct in the 17th century.

Australopithecus
The immediate predecessor of genus Homo.

Babakotia
A pint-sized "sloth lemur" from Madagascar.

Baiji
This dolphin once lived in the Yangtze River.

Bali Tiger
This Indonesian tiger went extinct 50 years ago.

Barbary Lion
An extinct lion of northern Africa.

Barbourofelis
The biggest of the "false" saber-toothed cats.

Barylambda
This Paleocene pantodont was eventually replaced by Coryphodon.

Barytherium
This ancient elephant sported eight short, stubby tusks.

Basilosaurus
The biggest prehistoric whale that ever lived.

Bison Latifrons (Giant Bison)
A Mammoth-sized bison of the late Pleistocene.

Bluebuck
This antelope was hunted to extinction 200 years ago.

Borhyaena
A large, hyena-like marsupial from South America.

Borophagus
One of the biggest of the bone-crushing canids.

Branisella
The oldest "new world" monkey yet identified.

Brontotherium (Megacerops)
The biggest of the Eocene "thunder beasts."

Brygmophyseter
Also known as the "biting sperm whale."

Camelops
The last camel ever to live in North America.

Cape Lion
A recently extinct lion of South Africa.

Caribbean Monk Seal
Christopher Columbus called it the "sea wolf."

Caspian Tiger
A recently extinct tiger of central Asia.

Castorocauda
This early mammal is known as the "Jurassic beaver."

Cave Bear (Ursus Spelaeus)
Guess where this prehistoric bear spent most of its time?

Cave Hyena (Crocuta Crocuta Spelaea)
This hyena competed with early humans for living space.

Cave Lion (Panthera Leo Spelaea)
The biggest lion that ever lived.

Cetotherium
A sleek ancestor of the modern gray whale.

Chalicotherium
It looked like a cross between a horse and a gorilla.

Chamitataxus
A prehistoric badger of the Miocene epoch.

Chriacus
This ancient mammal had a raccoon-like tail.

Cimexomys
Did this tiny mammal feast on Troodon eggs?

Cimolestes
The tiny ancestor of all modern-day carnivores.

Coryphodon
One of the most common mammals of the early Eocene epoch.

Cotylocara
Was this the first whale with the ability to echolocate?

Cronopio
Better known as the saber-toothed squirrel.

Crusafontia
This early mammal had some squirrel-like characteristics.

Cuvieronius
One of the few prehistoric elephants to have lived in South America.

Cynodictis
This was once thought to be the first true dog.

Daeodon (Dinohyus)
This prehistoric pig was the size of a rhinoceros.

Darwinius
Did this ancient primate lay at the root of human evolution?

Deinogalerix
A giant hedgehog of the Miocene epoch.

Deinotherium
One of the largest mammals ever to roam the earth.

Desmostylus
A strange, hippopotamus-like creature of the Miocene epoch.

Diacodexis
An ancient ancestor of even-toed ungulates.

Didelphodon
A Cretaceous ancestor of the modern opossum.

Dinictis
This leopard-like cat roamed the plains of North America.

Dinofelis
This jaguar-sized cat may have preyed on early hominids.

Dinohippus
This prehistoric horse wasn't quite as fearsome as its name.

Diprotodon (Giant Wombat)
This prehistoric wombat was the size of a rhinoceros.

Dire Wolf (Canis Dirus)
A giant wolf of the Pleistocene epoch.

Docodon
Perhaps not a true mammal, but a "mammal-like reptile."

Doedicurus
A gigantic, spike-tailed armadillo of the Pleistocene epoch.

Dormaalocyon
This ancient mammal was ancestral to modern cats and dogs.

Dorudon
This small whale was once mistaken for a baby Basilosaurus.

Dryopithecus
Guess where this "tree ape" spent most of its time?

Dusicyon (Warrah)
This "foolish dog" went extinct in the 19th century.

Dwarf Elephant
This pint-sized proboscid went extinct 10,000 years ago.

Ekaltadeta
Otherwise known as the saber-toothed rat kangaroo.

Elasmotherium
This prehistoric rhino may have inspired the unicorn legend.

Embolotherium
This "battering ram beast" had a bizarre head ornament.

Enaliarctos
This ancient pinniped pursued a wide variety of prey.

Entelodon (Killer Pig)
A giant pig of the Eocene epoch.

Eobasileus
This giant mammal was closely related to Uintatherium.

Eomaia
This early mammal is known from a single, spectacular fossil.

Eosimias
This "dawn monkey" was only a few inches long.

Eozostrodon
This Triassic critter may (or may not) have been the first true mammal.

Epicyon
This prehistoric dog was built more like a big cat.

Epihippus
This tiny, prehistoric horse lived 30 million years ago.

Eremotherium
Otherwise known as the Pan-American Ground Sloth.

Ernanodon
This tiny burrower was ancestral to modern pangolins.

Eucladoceros
This prehistoric deer had a distinctive set of antlers.

Eucyon
The immediate predecessor of modern canines.

Eurhinodelphis
A prehistoric dolphin with a swordfish-like snout.

European Lion
This big cat went extinct 1,000 years ago.

Eurotamandua
A three-foot-long, prehistoric anteater.

Eusmilus
This cat's canines were almost as long as its entire skull.

Fruitafossor
The earliest digging mammal yet discovered.

Gagadon
This early Eocene mammal was named after Lady Gaga.

Ganlea
Does it imply an Asian origin for anthropoids?

Georgiacetus
Guess what state this ancient whale was discovered in?

Giant Beaver (Castoroides)
This giant beaver weighed about 200 pounds.

Giant Ground Sloth (Megalonyx)
The bones of this giant sloth were discovered by Thomas Jefferson.

Giant Hyena (Pachycrocuta)
It was three times the size of a modern hyena.

Giant Short-Faced Bear (Arctodus Simus)
One of the largest bears that ever lived.

Gigantopithecus
This "giant ape" was twice the size of modern gorillas.

Glossotherium
This prehistoric sloth's bones have been found in the La Brea Tar Pits.

Glyptodon
This armadillo was the size of a Volkswagen Beetle.

Gomphotherium
One of the earliest shovel-toothed elephants.

Hadrocodium
This tiny mammal had an unusually large brain.

Hadropithecus
Yet another ancient lemur from Madagascar.

Hapalops
A sheep-sized ancestor of the Giant Sloth.

Hemicyon
This "half-dog" was more closely related to modern bears.

Hesperocyon
An early ancestor of the modern dog.

Hipparion
One of the most successful horses of the Miocene epoch.

Hippidion
This donkey-sized horse had a prominent snout.

Homotherium
The last specimen of this "scimitar cat" died 10,000 years ago.

Hoplophoneus
This "armed murderer" leaped on its prey from high trees.

Horned Gopher (Ceratogaulus)
This two-horned gopher looked like a miniature rhinoceros.

Hyaenodon
This fearsome carnivore was the Eocene equivalent of a wolf.

Hypohippus
This Miocene horse had unusually short legs.

Hyrachyus
An ancient ancestor of modern tapirs.

Hyracodon
This ancient rhinoceros looked more like a horse.

Hyracotherium (Eohippus)
The horse formerly known as Eohippus.

Icaronycteris
The earliest bat yet known from the fossil record.

Ictitherium
One of the first ground-dwelling hyenas.

Indohyus
This ancient hoofed creature may (or may not) have been ancestral to whales.

Indricocotherium (Paraceratherium)
The largest land mammal that ever lived.

Irish Elk (Megaloceros)
This prehistoric deer had dinosaur-sized antlers.

Janjucetus
This prehistoric whale looked more like a dolphin.

Javan Tiger
A recently extinct tiger of Indonesia.

Josephoartigasia
The largest rodent ever to walk the earth.

Juramaia
The earliest known placental mammal in the fossil record.

Kentriodon
This toothed whale was ancestral to the Bottlenose Dolphin.

Kretzoiarctos
The earliest known ancestor of the Giant Panda.

Kutchicetus
A long-tailed relative of the early whale Ambulocetus.

Leptictidium
A small, jumping mammal of the Eocene epoch.

Leptocyon
A tiny, foxlike ancestor of the modern dog.

Leptomeryx
This tiny ruminant was native to North America.

Leviathan (Livyatan)
A killer sperm whale of the Miocene epoch.

Liaoconodon
This early mammal had a transitional inner ear.

Machairodus
One of the earliest of the true sabre-toothed cats.

Macrauchenia
It looked like horse crossed with a camel crossed with an elephant.

Maiacetus
This prehistoric whale gave birth on land.

Mammalodon
Did this ancient whale suck up prey on the sea floor?

Maotherium
This early mammal was named after Mao Zhedong.

Mastodon (Mammut)
Its most famous species was the North American Mastodon.

Megaconus
This "mammaliform" l lived during the late Jurassic period.

Megaladapis
This prehistoric lemur weighed over 100 pounds.

Megantereon
One of the most successful predators of the prehistoric plains.

Megatherium (Giant Sloth)
This prehistoric sloth was bigger than an elephant.

Megazostrodon
A transitional form between therapsids and true mammals.

Megistotherium
One of the biggest carnivores of the Miocene epoch.

Menoceras
The first prehistoric rhino to evolve horns.

Merychippus
An important intermediate step in equine evolution.

Merycoidodon
A distant relative of modern camels.

Mesohippus
This "middle horse" was about the size of a deer.

Mesonyx
This wolf-like predator may have been ancestral to whales.

Mesopithecus
This Pliocene monkey resembled a modern macaque.

Metailurus
A sleeker relative of Dinofelis.

Metamynodon
This rhinoceros looked more like a hippopotamus.

Metridiochoerus
Otherwise known as the Giant Warthog.

Miacis
One of the oldest carnivorous mammals yet identified.

Miohippus
This "Miocene horse" actually lived much earlier.

Moeritherium
This ancient elephant was about the size of a pig.

Morganucodon
Another early mammal of the late Triassic period.

Moropus
This "stupid-footed" mammal was a close relative of Chalicotherium.

Mylodon
This prehistoric sloth weighed "only" about 500 pounds.

Myotragus (Cave Goat)
Did this strange goat have a cold-blooded metabolism?

Necrolemur
A big-eyed tarsier of the Eocene epoch.

Necrolestes
It took over 100 years for this mammal to be identified.

Nesodon
This "island tooth" was a close relative of Toxodon.

Nimravus
A prehistoric cat with some hyena-like qualities.

Notharctus
This lemur-like primate lived 50 million years ago.

Nuralagus
The biggest rabbit that ever lived.

Obdurodon
This prehistoric platypus had a toothed bill.

Oligokyphus
An extremely mammal-like reptile of the early Jurassic.

Onychonycteris
One of the earliest bats in the fossil record.

Oreopithecus
Paleontologists call it the "cookie monster."

Orohippus
This prehistoric horse was a close relative of Hyracotherium.

Ouranopithecus (Graecopithecus)
This prehistoric ape was discovered in Greece.

Pakicetus
This dog-like mammal was ancestral to modern whales.

Palaeocastor
This ancient beaver lived in deep burrows.

Palaeochiropteryx
A prehistoric bat of Eocene Europe.

Palaeolagus
This "ancient rabbit" was the same size as its modern descendants.

Palaeomastodon
One of the earliest elephant-like proboscids.

Palaeopropithecus
This "sloth lemur" looked like a cross between...

Palaeotherium
This tapir-like beast was remotely related to modern horses.

Paleoparadoxia
This "ancient puzzle" was a dead end in mammal evolution.

Palorchestes
A close relative of the Giant Wombat.

Parahippus
This "almost horse" had noticeably enlarged middle toes.

Paranthropus
A bigger, smarter version of Australopithecus.

Pelorovis
Its name is Greek for "monstrous sheep."

Peltephilus
A five-foot-long, two-horned armadillo.

Phascolonus
A more petite cousin of the Giant Wombat.

Phenacodus
One of the first hooved mammals to appear on earth.

Phiomia
An early ancestor of modern elephants.

Phosphatherium
The earliest known ancestor of modern elephants.

Pierolapithecus
Was this the common ancestor of great apes and lesser apes?

Pig-Footed Bandicoot
A tiny--and strange--Australian marsupial.

Platybelodon
This prehistoric elephant came equipped with its own spork.

Platygonus
An ancient ancestor of the modern peccary.

Plesiadapis
One of the earliest primates yet discovered.

Pliohippus
This prehistoric horse was built for speed.

Pliopithecus
One of the first ancient primates ever to be identified.

Poebrotherium
A deer-like camel of Oligocene North America.

Potamotherium
Was it ancestral to seals or weasels?

Primelephas
The immediate predecessor of the modern elephant.

Proailurus
Could this have been the ancestor of all modern cats?

Proconsul
Could this have been the first true ape?

Procoptodon
Better known as the Giant Short-Faced Kangaroo.

Propleopus
A meat-eating ancestor of the rat kangaroo.

Propliopithecus (Aegyptopithecus)
This early ape resembled a small gibbon.

Prorastomus
An ancient ancestor of modern dugongs and manatees.

Protemnodon
A six-foot wallaby of Pleistocene Australia.

Protoceras
The earliest of the deer-like "protoceratids."

Protocetus
This "first whale" looked more like a seal.

Pseudaelurus
A direct (but ancient) ancestor of modern cats.

Ptilodus
A squirrel-like mammal with a prehensile tail.

Puijila
The earliest known ancestor of modern seals.

Purgatorius
Could this have been the direct ancestor of human beings?

Pyrotherium
This "fire beast" resembled a baby elephant.

Quagga
This South African zebra went extinct in 1883.

Remingtonocetus
Yet another prehistoric whale from modern-day Pakistan.

Repenomamus
The only early mammal known to have hunted dinosaurs.

Rodhocetus
Yet another early step in the evolution of whales.

Rugosodon
The oldest multituberculate yet discovered.

Saadanius
This primate "missing link" was discovered in Saudi Arabia.

Samotherium
A short-necked giraffe of the Miocene epoch.

Sarkastodon
No, it wasn't any more sarcastic than any other prehistoric mammal.

Semirostrum
This prehistoric porpoise had a gigantic underbite.

Shrub-Ox
One of the first bovids to be native to North America.

Simosthenurus
A 200-pound kangaroo of the Pleistocene epoch.

Sinoconodon
Another intermediate form between reptiles and mammals.

Sinodelphys
One of the earliest marsupials yet discovered.

Sinonyx
This hooved carnivore lived a few million years after the dinosaurs.

Sivapithecus (Ramapithecus)
This primate may have been ancestral to modern orangutans.

Sivatherium
This prehistoric giraffe looked more like a moose.

Smilodectes
A lemur-like primate from North America.

Smilodon (Saber-Toothed Tiger)
What most folks know as the "saber-toothed tiger."

Squalodon
This "shark-toothed" mammal was actually an ancestral whale.

Stag Moose (Cervalces Scotti)
A giant, moose-like deer of North America.

Stegomastodon
Not quite a cross between a Stegosaurus and a mastodon.

Stegotetrabelodon
This elephant's footprints have been found in the Arabian peninsula.

Steller's Sea Cow (Hydrodamalis)
A prehistoric ancestor of modern dugongs and manatees.

Stephanorhinus
A two-horned rhino of Pleistocene Eurasia.

Steropodon
An ancient ancestor of the modern platypus.

Sthenurus
A giant kangaroo of Pleistocene Australia.

Straight-Tusked Elephant (Elephas Antiquus)
This elephant species went extinct 50,000 years ago.

Syndyoceras
A deer-like mammal with a V-shaped horn on its snout.

Synthetoceras
This mammal came equipped with its own salad fork.

Taeniolabis
The biggest of the "multituberculate" mammals.

Tarpan
The immediate predecessor of the modern horse.

Tasmanian Tiger
The largest marsupial predator of modern times.

Teinolophos
An early ancestor of the modern platypus.

Teleoceras
A hippo-like rhinoceros of the Miocene epoch.

Tetralophodon
A widespread elephant of the Miocene epoch.

Thalassocnus
A marine sloth of Pliocene South America.

Thylacoleo (Marsupial Lion)
The largest carnivorous mammal ever to live in Australia.

Thylacosmilus
A marsupial variant of the saber-toothed cat.

Titanotylopus
A giant camel of the Pliocene epoch.

Tomarctus
A bone-crushing dog of the Miocene epoch.

Toxodon
A strange, rhino-like beast from South America.

Triconodon
A common mammal of the late Jurassic.

Trigonias
A hornless rhinoceros of the Oligocene epoch.

Uintatherium
This rhino-like mammal sported three pairs of horns.

Wakaleo
A smaller cousin of the Marsupial Lion.

Woolly Mammoth (Mammuthus)
This shaggy beast was hunted by early humans.

Woolly Rhino (Coelodonta)
A shaggy rhinoceros of the Pleistocene epoch.

Xenosmilus
This unclassifiable saber-tooth was discovered in Florida.

Zalambdalestes
This tiny mammal may be the ancestor of modern rodents.

Zygomaturus
A giant marsupial of Pleistocene Australia.

Zygorhiza
This early whale may have crawled onto land to give birth.

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