Historical Geology 102
Life in the Cenozoic

Cenozoic Era "Age of Mammals"

Evolutionary history of mammals is very well known
Terrestrial deposits are more common for the Cenozoic than from the Paleozoic or Mesozoic
Well preserved fossils


Angiosperms continue to dominate and diversify
Most significant plant evolutionary event - grass diversifies - Miocene (24-5 m.y.)
Grassland and prairies develop
Results in major evolutionary changes in mammals


Dental structure and dental growth patterns changed in some mammals
Grass is very abrasive
Teeth need to grow continuously
Skull and jaw morphology change
Larger teeth require different jaw structure - skull modification for new jaw structure
Grass is difficult to digest
4 chambered stomach evolves
Grasslands do not provide cover from predators
Skeletal modification for faster running
Faster flight of prey resulted in faster predators evolving


Evolved in the Triassic
Late Cretaceous - 8 Families of marsupial and placental mammals
Diversification after the K-T extinction
Rodent-like animals during the Mesozoic
Possess certain attributes which distinguish mammals from other organisms

Pleistocene Mammals

Giant species became common
Mastodons, mammoths, giant bison, giant ground sloths, giant camels, giant beavers, giant kangaroos and the Irish elk
Larger size may have been in response to cooler temperature during Pleistocene glaciation

Large Mammal Extinction

10,000 year ago nearly all large terrestrial mammals of North and South America and Australia became extinct.
Unusual extinction in that it only affected large mammals
Two main theories for this extinction:

Climatic Change

Rapid climatic change at the end of the most recent glacial maximum - warmer temperatures
Changing vegetation
Why didn't the large mammals migrate to cooler climates?
Why aren't there similar extinctions during prior interglacial periods?

Prehistoric Overkill Theory

Mass extinction coincides with the arrival of humans in North America, South America and Australia
Hunting practices killed off the large mammals
Large mammals - unfamiliar with humans and had not developed natural defenses against them

Overkill Theory: Problems

Early human migrations were in small groups
Could they have killed off large populations?

Additional information may be obtained at: Cenozoic Life I
Additional information may be obtained at: Cenozoic Life II