Earth Science 13.4 Cenozoic Era : Age of Mammals
Cenozoic Era :
The Age
of
Mammals
The Age of Mammals
The Age of Mammals: (65 m –
present)
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If the Mesozoic was the “Age of
reptiles” the Cenozoic can be called
the “Age of Mammals”.
During the Mesozoic, mammals were
mainly small scavengers and plant
eaters.
After the Cretaceous extinction,
mammals began to adapt to
environments and expand in their
diversity.
Mammals of the Cenozoic
The Age of Mammals
The Age of Mammals:
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Mammals succeeded during the
Cenozoic because of adaptations
that enabled them to out compete
the surviving reptiles.
For example, because mammals are
warm-blooded, they can live in cold
environments and search for food
any time of day or time of year.
Other adaptations include more
efficient hearts and lungs than
reptiles, and the development of
insulating body hair or fur.
These adaptations allowed
mammals to lead more active lives
than reptiles.
Mammals of the Cenozoic
The Age of Mammals
The Tertiary Period:
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During the Tertiary period (65 – 1.5
million), mountain building and
climate changes accompanied the
breakup of Pangaea. Mammals
became widespread and diverse
worldwide.
Major fragments of Pangaea became
separate continents during the
Tertiary.
Seas separated North America from
South America and Europe from
Africa.
Plate movements led to major
mountain building activity in western
North America (the Rockies), Europe
(the Alps) and India (the Himalayas).
The Age of Mammals
The Tertiary Period:
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Generally, climates during the
Tertiary period were cooler than
those of the Cretaceous.
The mid-Tertiary had temperate
dry climates.
Later in the period, Earth’s
climates cooled leading to the
development of large continental
glaciers in Antarctica about 10
million years ago.
The Age of Mammals
Tertiary Life:
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The Tertiary saw the development
of many new species, from
songbirds to snakes.
The major development of the
Tertiary was the evolution of many
new types of mammals.
Mammals evolved specialized limbs
and teeth for particular
environments.
For example, meat-eaters evolved
sharp teeth for cutting and
tearing. Rodents developed selfsharpening teeth for gnawing. Plant
eaters developed flat molars for
chewing.
The Age of Mammals
Tertiary Life:
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Some animals evolved to take
advantage of a rich new food
source; grass.
As the climate became cooler and
drier, vast grasslands developed.
Many types of grazing animals,
including the ancestors of cattle
and horses, evolved during the
Tertiary.
The Age of Mammals
Quaternary Period: (5.3 – 0)
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Two factors have greatly affected
life on Earth during the
Quaternary period :
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The advance and retreat of
continental glaciers (which have
formed and melted about 30 times
in the last 3 million years)
 And the migration of homo sapiens
(humans) to every corner of the
Earth
The Age of Mammals
Quaternary Period: (5.3 – 0)
 A map showing the physical features of Earth 2 million years ago would
look much the same today.
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But beginning in the late tertiary, a series of ice ages covered large
parts of the northeast hemisphere with continental glaciers.
The Age of Mammals
Quaternary Period: (5.3 – 0)
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Because Earth is a complex system,
many factors determine whether
Earth’s climate becomes cold enough
for an ice age.
These factors include ocean
currents, the size of the ice covered
areas, and the affects of living
things on the atmosphere.
The Age of Mammals
Quaternary Period: (5.3 – 0)
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In the 1940’s, astronomer Milutin
Milankovitch proposed that three
different cycles, related to Earth’s
movements, were the main cause of
ice ages.
These cycles are called the
Milankovitch cycles.
The Age of Mammals
Quaternary Period: (5.3 – 0)
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For example, there is a 100,000 year
cycle related to changes in the shape
of the Earth’s orbit.
Earth receives more or less energy
from the sun depending on it’s
position within each of these cycles.
The Age of Mammals
Quaternary Period: (5.3 – 0)
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Milankovitch thought that ice ages
occur when solar energy reaching
Earth is at a minimum.
Scientists today think that
Milankovitch cycles provide a
“partial” explanation for recent ice
ages.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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One trend in evolution during both
the Tertiary and Quaternary periods
was that some mammals became very
large.
During the ice ages, many large
mammals lived in the cold grasslands,
or steppe, that bordered the ice
covered regions of North America.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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These animals included mastodons
and mammoths, which were both
huge ancestors of the elephant.
In North America, there were also
giant beavers, ground sloths, wolves.
bears, sabre-tooth cats and bison.
All these animals became extinct
about 10,000 years ago, at the end
of the last ice age.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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How can the extinction at the end of
this last ice age have occurred?
Scientists have multiple theories. No
single explanation provides a
complete answer.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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Some scientists suggest disease or
climate change played an important
role in their demise.
Still other scientists suggest that
humans hunted large animals down to
the point of extinction.
Other skeptics question whether
small groups of humans could have
caused so many different species to
all go extinct all at once.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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Modern Homo sapiens evolved from
ancestors in Africa more than
100,000 years ago.
The fossil record shows that about
50,000 years ago early humans began
to migrate out of Africa.
Soon, the range of early humans
extended from Europe, Africa, and
Asia to Australia.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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Than, as sea level fell during the last
ice age, a land bridge formed that
connected Asia with North America.
Scientists think this land bridge
enabled humans to migrate to the
Americas about 14,000 years ago.
The Age of Mammals
Quaternary Life: (5.3 – 0)
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Today, Homo sapiens - humans
inhabit every continent. Our species
has become the most powerful
factor in changing Earth’s
environment; for the better or
worse.
This in turn affects the other
species with whom we share the
planet.