Prehistoric Mammals - Mammals of the Mesozoic and Cenozoic Eras
Dinosaurs weren't the only land animals of the Mesozoic and Cenozoic eras. Here are profiles of the early, mouse-sized mammals that coexisted with these enormous beasts, as well as the sabre-toothed cats, mammoths, sloths, and other giant mammals that succeeded them.
Aetiocetus
This primitive whale used both teeth and plankton-filtering baleen.
This primitive whale used both teeth and plankton-filtering baleen.
Alphadon
An early marsupial of the late Cretaceous.
An early marsupial of the late Cretaceous.
Ambulocetus
This "walking whale" led an otter-like lifestyle.
This "walking whale" led an otter-like lifestyle.
Amebelodon
This "shovel-toothed" elephant thrived in flooded lowlands.
This "shovel-toothed" elephant thrived in flooded lowlands.
Anancus
This early elephant's tusks were as long as its entire body.
This early elephant's tusks were as long as its entire body.
Anchitherium
A long-lived "side branch" on the equine tree of life.
A long-lived "side branch" on the equine tree of life.
Barytherium
This ancient elephant sported eight short, stubby tusks.
This ancient elephant sported eight short, stubby tusks.
Basilosaurus
The biggest prehistoric whale that ever lived.
The biggest prehistoric whale that ever lived.
Castorocauda
This early mammal is known as the "Jurassic beaver."
This early mammal is known as the "Jurassic beaver."
Castoroides
Better known as the Giant Beaver.
Better known as the Giant Beaver.
Cetotherium
A sleek ancestor of the modern gray whale.
A sleek ancestor of the modern gray whale.
Cimexomys
Did this tiny mammal feast on Troodon eggs?
Did this tiny mammal feast on Troodon eggs?
Cimolestes
The tiny ancestor of all modern-day carnivores.
The tiny ancestor of all modern-day carnivores.
Crusafontia
This early mammal had some squirrel-like characteristics.
This early mammal had some squirrel-like characteristics.
Cuvieronius
One of the few prehistoric elephants to have lived in South America.
One of the few prehistoric elephants to have lived in South America.
Deinotherium
One of the largest mammals ever to roam the earth.
One of the largest mammals ever to roam the earth.
Dinictis
This leopard-like cat roamed the plains of North America.
This leopard-like cat roamed the plains of North America.
Dinofelis
This jaguar-sized cat may have preyed on early hominids.
This jaguar-sized cat may have preyed on early hominids.
Dinohippus
This prehistoric horse wasn't quite as fearsome as its name.
This prehistoric horse wasn't quite as fearsome as its name.
Docodon
Perhaps not a true mammal, but a "mammal-like reptile."
Perhaps not a true mammal, but a "mammal-like reptile."
Dorudon
This small whale was once mistaken for a baby Basilosaurus.
This small whale was once mistaken for a baby Basilosaurus.
Eomaia
This early mammal is known from a single, spectacular fossil.
This early mammal is known from a single, spectacular fossil.
Eozostrodon
This Triassic critter may (or may not) have been the first true mammal.
This Triassic critter may (or may not) have been the first true mammal.
Epihippus
This tiny, prehistoric horse lived 30 million years ago.
This tiny, prehistoric horse lived 30 million years ago.
Eusmilus
This cat's canines were almost as long as its entire skull.
This cat's canines were almost as long as its entire skull.
Fruitafossor
The earliest digging mammal yet discovered.
The earliest digging mammal yet discovered.
Gomphotherium
One of the earliest shovel-toothed elephants.
One of the earliest shovel-toothed elephants.
Hadrocodium
This tiny mammal had an unusually large brain.
This tiny mammal had an unusually large brain.
Hipparion
One of the most successful horses of the Miocene epoch.
One of the most successful horses of the Miocene epoch.
Hippidion
This donkey-sized horse had a prominent snout.
This donkey-sized horse had a prominent snout.
Homotherium
The last specimen of this "scimitar cat" died 10,000 years ago.
The last specimen of this "scimitar cat" died 10,000 years ago.
Hoplophoneus
This "armed murderer" leaped on its prey from high trees.
This "armed murderer" leaped on its prey from high trees.
Hyracotherium
The horse formerly known as Eohippus.
The horse formerly known as Eohippus.
Indohyus
This ancient hoofed creature may (or may not) have been ancestral to whales.
This ancient hoofed creature may (or may not) have been ancestral to whales.
Kutchicetus
A long-tailed relative of the early whale Ambulocetus.
A long-tailed relative of the early whale Ambulocetus.
Machairodus
One of the earliest of the true sabre-toothed cats.
One of the earliest of the true sabre-toothed cats.
Maiacetus
This prehistoric whale gave birth on land.
This prehistoric whale gave birth on land.
Mammut (Mastodon)
Better known as the North American mastodon.
Better known as the North American mastodon.
Mammuthus (Woolly Mammoth)
The one, and only, woolly mammoth.
The one, and only, woolly mammoth.
Megalonyx
The bones of this giant sloth were discovered by Thomas Jefferson.
The bones of this giant sloth were discovered by Thomas Jefferson.
Megantereon
One of the most successful predators of the prehistoric plains.
One of the most successful predators of the prehistoric plains.
Megazostrodon
A transitional form between therapsids and true mammals.
A transitional form between therapsids and true mammals.
Merychippus
An important intermediate step in equine evolution.
An important intermediate step in equine evolution.
Mesohippus
This "middle horse" was about the size of a deer.
This "middle horse" was about the size of a deer.
Miohippus
This "Miocene horse" actually lived much earlier.
This "Miocene horse" actually lived much earlier.
Moeritherium
This ancient elephant was about the size of a pig.
This ancient elephant was about the size of a pig.
Morganucodon
Another early mammal of the late Triassic period.
Another early mammal of the late Triassic period.
Nimravus
A prehistoric cat with some hyena-like qualities.
A prehistoric cat with some hyena-like qualities.
Oligokyphus
An extremely mammal-like reptile of the early Jurassic.
An extremely mammal-like reptile of the early Jurassic.
Orohippus
This prehistoric horse was a close relative of Hyracotherium.
This prehistoric horse was a close relative of Hyracotherium.
Pakicetus
This dog-like mammal was ancestral to modern whales.
This dog-like mammal was ancestral to modern whales.
Palaeomastodon
One of the earliest elephant-like proboscids.
One of the earliest elephant-like proboscids.
Palaeotherium
This tapir-like beast was remotely related to modern horses.
This tapir-like beast was remotely related to modern horses.
Parahippus
This "almost horse" had noticeably enlarged middle toes.
This "almost horse" had noticeably enlarged middle toes.
Phiomia
An early ancestor of modern elephants.
An early ancestor of modern elephants.
Phosphatherium
The earliest known ancestor of modern elephants.
The earliest known ancestor of modern elephants.
Platybelodon
This prehistoric elephant came equipped with its own spork.
This prehistoric elephant came equipped with its own spork.
Pliohippus
This prehistoric horse was built for speed.
This prehistoric horse was built for speed.
Primelephas
The immediate predecessor of the modern elephant.
The immediate predecessor of the modern elephant.
Proailurus
Could this have been the ancestor of all modern cats?
Could this have been the ancestor of all modern cats?
Protocetus
This "first whale" looked more like a seal.
This "first whale" looked more like a seal.
Purgatorius
Could this have been the direct ancestor of human beings?
Could this have been the direct ancestor of human beings?
Repenomamus
The only early mammal known to have hunted dinosaurs.
The only early mammal known to have hunted dinosaurs.
Rodhocetus
Yet another early step in the evolution of whales.
Yet another early step in the evolution of whales.
Sinoconodon
Another intermediate form between reptiles and mammals.
Another intermediate form between reptiles and mammals.
Sinodelphys
One of the earliest marsupials yet discovered.
One of the earliest marsupials yet discovered.
Smilodon
What most folks know as the "sabre-toothed tiger."
What most folks know as the "sabre-toothed tiger."
Stegomastodon
Not quite a cross between a Stegosaurus and a mastodon.
Not quite a cross between a Stegosaurus and a mastodon.
Teinolophos
An early ancestor of the modern platypus.
An early ancestor of the modern platypus.
Thylacosmilus
A marsupial variant of the sabre-toothed cat.
A marsupial variant of the sabre-toothed cat.
Triconodon
A common mammal of the late Jurassic.
A common mammal of the late Jurassic.
Xenosmilus
This unclassifiable sabre-tooth was discovered in Florida.
This unclassifiable sabre-tooth was discovered in Florida.
Zalambdalestes
This tiny mammal may be the ancestor of modern rodents.
This tiny mammal may be the ancestor of modern rodents.
Zygorhiza
This early whale may have crawled onto land to give birth.
This early whale may have crawled onto land to give birth.