Small Animal Care & Management - Fourth Edition - 4

Section I

Period

Epoch

Years before
present (B.P.)

Geologic events

Events refer especially to North America and
do not reflect great worldwide variations

Hadean
Archeon
Proterozoic

Fossil algae; other fossils
extremely rare; evidence of
sponges and worm burrows

4.5 billion
3.8 billion
2.5 billion

Volcanic activity; mountain
building; glaciations;
variable climate

Origin of many invertebrate phyla
and classes; trilobites dominant;
marine algae

600 million

Cambrian

Three periods of land
submergence; mild

Ostracoderms (first vertebrates);
abundant marine invertebrates;
first land plants

500 million

Submergence of land; warm

Ordovician
Silurian

First jawed fishes

425 million

Continental seas and reefs; mild

Devonian

First amphibians; freshwater fishes
abundant; bryozoans and corals

405 million

Inland seas; first forests; mild

Radiation of amphibians;
abundant sharks; scale trees and
seed ferns

345 million

Mississippian

Inland seas; warm to hot;
swamplands

Pennsylvanian

First reptiles; giant insects; great
conifer forests

310 million

Shallow inland seas; extensive coal
deposits; warm and moist

280 million

Permian

Radiation of reptiles; ;
displacement of amphibians;
extinction of many marine
invertebrates

Continents elevated; building of
Appalachians; cold and dry

Triassic

First dinosaurs; mammal-like
reptiles; conifers dominate plants

230 million

Continents elevated; widespread
deserts; cool and dry

First birds; first mammals;
dinosaurs abundant

180 million

Continents with shallow seas,
building of Sierra Nevada
mountains; cool then mild

Climax of giant land and marine
reptiles, followed by extinction;
flowering plants; decline of gymnosperms

135 million

Spread of inland seas and swamps;
building of Andes, Himalayas,
Rockies; mild to cool

Paleocene

First placental mammals

70 million

Mountain building; subtropical

Eocene

Radiation of placentals

60 million

Mountain erosion; rain and mild

Oligocene

Apes, monkeys, whales

40 million

Mountain erosion; mild

Miocene

Abundant grazing mammals

25 million

Plains and grasslands; moderate

Pliocene

Large carnivores

7 million

Continental elevation; cool

Pleistocene

Early man

Recent

Modern man

Carboniferous

MESOZOIC

Biologic events

Jurassic

Cretaceous

Tertiary

Quaternary

0.5 to 3 million

Ice ages; then warmer

11 thousand

The history of the earth is divided into periods of time. This geologic time chart shows the geologic
events that occurred in North America and the living organisms that were present during the geologic events.

Figure 1-1

Ordovician period and became abundant during the Devonian period.
See Figure 1-2.
During the Triassic period, between 230 and 180 million years ago,
dinosaurs appeared, along with mammal-like reptiles. The first birds and
mammals appeared between 180 and 135 million years ago during the
Jurassic period, when dinosaurs became abundant. Most paleontologists

© Cengage Learning®

PALEOZOIC

PRECAMBRIAN

Era

CENOZOIC

4



Table of Contents for the Digital Edition of Small Animal Care & Management - Fourth Edition

Contents
Small Animal Care & Management - Fourth Edition - Cover1
Small Animal Care & Management - Fourth Edition - Cover2
Small Animal Care & Management - Fourth Edition - iii
Small Animal Care & Management - Fourth Edition - iv
Small Animal Care & Management - Fourth Edition - Contents
Small Animal Care & Management - Fourth Edition - vi
Small Animal Care & Management - Fourth Edition - vii
Small Animal Care & Management - Fourth Edition - viii
Small Animal Care & Management - Fourth Edition - ix
Small Animal Care & Management - Fourth Edition - x
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Small Animal Care & Management - Fourth Edition - xviii
Small Animal Care & Management - Fourth Edition - xix
Small Animal Care & Management - Fourth Edition - xx
Small Animal Care & Management - Fourth Edition - xxi
Small Animal Care & Management - Fourth Edition - xxii
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