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

Invertebrates

Evolutionary diversification of many groups after mass extinction at the end of the Mesozoic
Foraminifera, radiolarians, corals, bryozoans, mollusks and echinoids
Lack of broad, shallow epicontinental seas restricted marine life to narrow continental margins

Birds

Increased diversification
Owls, hawks, ducks penguins and vultures evolved in the early Tertiary
Today - great variation in size and adaptations
Basic skeletal structure has not changed much - birds are primarily fliers
This restricts modifications to the skeleton
Too much change and it won't fly
Major structural change did occur in the evolution of the large flightless predatory birds
- Diatryma
Ostrich, emu and rhea are present descendants

Fish, Amphibians and Reptiles

Have not undergone major evolutionary changes during the Cenozoic
Fish diversity has increased during the Cenozoic
Amphibians have remained essentially unchanged for 200 million years
Reptiles have also seen relatively little change
Turtles first evolved in the Permian
Crocodiles evolved in the Triassic
Snakes evolved in the Mesozoic
Poisonous snakes evolved in the Miocene
Specialized tooth structure for the injection of venom

Vegetation

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

Grass

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
Cheetah - max. speed 70 mph
Grass has diversified since first appearance
Cereal grains - wheat, rye, oats, corn, barley and rice
Bamboo is grass

Mammals

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
1) Homeothermic - warm blooded
2) Hair - insulation
3) Mammary glands for the production of milk - modified sweat gland

Mammal Groups

Three groups of mammals
1) Monotremes
2) Marsupials
3) Placentals

Monotremes

Considered to be "primitive" mammals
- believed by some to be recent evolutionary adaptations
Possess poorly developed mammary glands
Lay eggs, instead of bearing live young
Poor fossil record
Only 3 species exist today
Platypus, and 2 species of spiny anteaters

Marsupials

Bear live young which are born in a very immature state - nearly embryonic
Development after birth takes place in a marsupium (pouch)
Kangaroos, wallabies, wombats, koalas and opossums
First marsupials evolved during the Cretaceous
May have evolved in North America
Today - most abundant and diverse marsupials are found in Australia and South America
Both continents were isolated during the Tertiary
When put in the same environment with placental mammals, marsupials generally do not compete well for resources compared to the placental mammals

---