The Miocene Epoch (meaning "moderately recent") extends from approximately 23 million years ago until 5 million years ago. It was during the Miocene that a new ecological niche was filled, as grazing animals became common after the rise of grasses in the Oligocene. Both the grazers and their associated predators became fleet of foot to maneuver around the relatively protection-free grass plains.
Classic Fossil-Bearing Sites
Calvert Formation, Maryland
Agate Springs Fossil Beds, Nebraska
Twenty-one million years ago in western Nebraska the Niobrara River (now a mere trickle) was cutting valleys and laying down sand bars. The sediments carried by the river turned to rock over time, and the layer is now known as the Harrison Formation.
A severe multi-year drought struck the region at some point, concentrating the animals around the few remaining waterholes. Animals died by the thousands. When, eventually, the rains reappeared, the carcasses of the animals were swept downstream, congregating in river bends. The mass of bones was buried in the sand, to be discovered years later (1878) by roaming explorers. Two small hills still hold the remains of thousands of animals who died many years ago.
Three craterform structures are known from Miocene times. A 20 km crater from 21 million years ago is found in the Northwest Territories of Canada (with possible implication for the deaths at Agate Springs). A 24 km impact structure from 14.8 million years ago is located in Ries, Germany. And a 10 km crater from an impact 10 million years ago is found in Karla, Russia.
Miocene Graphics
| |
|
|
| Agate Springs, Nebraska |
Diceratherium cooki |
Cranioceras |
| |
|
|
| Trilophodon |
Moropus |
Return to Life Through Geologic Time
Return to Earth History Resources