The Cenozoic: the Mammals take over!

After the death of the Dinosaurs, no completely terrestrial animal larger than 100 pounds survived! There were large alligators and other aquatic or semi-aquatic animals, but no large terrestrial animals made the transition.

Monotremes (egg-laying mammals!) date back to before the middle Mesozoic. Those living today are ‘last survivors of a early line of Mammals.

5 species of Monotremes still exist today (4 of them are Echidnas).

Platypus

Echidna

Monotremes use Electrolocation to find prey, and lay reptile-like eggs. One Platypus gene is also found in birds!

…But…they wouldn’t be what you would think!

The World was populated by Mammals that would look vaguely familiar…

Mammals evolved rapidly in the early Cenozoic.

PLACENTAL mammals had evolved in the Mesozoic. Egg-laying mammals and Marsupials generally survived in isolated areas.

Rhinos that weren’t Rhinos…!

Cattle that weren’t Cattle…!

Predators living near the water started hunting in water more & more…and Whales evolved!

Small forest creatures with toes evolved rapidly when they left the woods...and Horses evolved!

…and Elephants evolved!

Small cattle-sized mammals became large…

And in some places…

Marsupials and Giant Birds ruled!

Paleocene

Eocene

Oligocene

Miocene

Pleistocene

Pliocene

Placentals

Multituberculates

Marsupials

Monotremes

The Age of Mammals?

LOTS of Birds and Reptiles, BTW…

Paleocene

Eocene

Oligocene

Miocene

Pleistocene

Pliocene

"Eocene" by Jay Matternes

Warm and wet…abundant forests.

Paleocene

Eocene

Oligocene

Miocene

Pleistocene

Pliocene

“Oligocene" by Jay Matternes

Later HorsesLater RhinocerosesLater CamelsEarly Seals

Climate cools and dries. Forests diminish… Plains habitat expands.

“Miocene" by Jay MatternesPaleocene

Eocene

Oligocene

Miocene

Pleistocene

PlioceneRecognizable:DogsBearsRaccoonsHorsesBeaverDeerCamelsWhales

Also:DucksOwls…

…and pretty much all modern Bird families.

Paleocene

Eocene

Oligocene

Miocene

Pleistocene

Pliocene

“Pliocene" by Jay Matternes

Extinction of many South American species

Oh yes… These things appeared.

Essentially a “modern-looking” fauna!

Early mammals evolved into new forms. A semi-aquatic predator we call “Pakicetus” gave rise to descendants that were better adapted to water.

Further changes lead to better adaptation to an aquatic life.

Fossil

Restored skeleton

Reconstructed animal

Later whales continued to have small legs. Even modern whales have back leg bones embedded in their bodies: a remnant of their terrestrial life.

The recently discovered Maiacetus…

…with child!

Comparison of Maiacetus

and Dorudon…

Notice the similar skulls.

4-legged ancestor of Manatee or “Sea Cow”.

Similarly, other mammals also developed aquatic features as they adapted to water. This is the skeleton of a Manatee…a “Sea Cow”…with LEGS! Visitors to Florida can see its descendants today.

Equus: Modern Horse

A long process over millions of years to produce what we call the “Horse”!

Early horses were small animals with 4 or 5 toes per foot…no hooves!

A little later; and a little more horse-like!

Early hooves allow faster running!

Roughly 4 million years ago…

…Human-like fossils appear.

And about 2 million years ago…the Ice Ages began! Paleocene

Eocene

Oligocene

Miocene

Pleistocene

Pliocene

Human Footprints

A vast mammalian fauna roamed the plains of North America. Much of the present USA looked like Africa of today!

Authentic reconstruction of ancient mammal?

Virtually all of the giant fauna became extinct at the end of the Ice Ages.

Why?

Both acting together? Stressed-out, starving, large mammals hunted to extinction?

People? (Improved technology?)

Climate? (loss of food, habitat?)

We’re not sure….!

But…we DO know that our ancestors had the technology… spears and spear-throwers… to hunt the largest game.

They left marvelous art in caves about their hunts.

We KNOW what Ice-Age animals looked like!

They left us pictures!