Life of the Cenozoic Era main points

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Life of the Cenozoic Era main points

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Title: Life of the Cenozoic Era main points

1
Chapter 18
Life of the Cenozoic Eramain points.1.
Angiosperms diversified, along with
invertebrates2. Early Tertiary climate in N
America was humid and warm, becoming more arid
thru time.3. marsupial and placental animals
evolved from common ancestor in Paleocene.4.
carnivorous mammals existed and evolved.5.
evolution of odd-toed and even-toed mammals very
well represented in fossil record.6. one trend
among Pleistocene mammals was toward huge size,
but most of these mammals are now extinct.7. as
Pangea continued to break up, intercontinental
migrations became more difficult.8. a Late
Cenozoic land connection between N America and S
America resulted in migrations in both directions.
2
Cenozoic Life History

The Cenozoic was the time during which
Earths present-day fauna and flora evolved
as trends established millions of years earlier
continued
For example, we see fewer skull bones
and fewer bones in the jaw during the transition
from fish to amphibians
and then to reptiles
and finally to mammals

3
Evolution of Mammals

But by Cenozoic time
mammals had clearly differentiated
from their ancestors
Mammals arose during the Late Triassic
but really started to diversify
following the end-of-Mesozoic extinctions

4
Other Biological Events

Other equally important biological events
were taking place
For instance, angiosperms
continued to dominate land plant communities
and now constitute more than 90 of all land
plants
Birds evolved during the Jurassic,
perhaps earlier, but the families now common
appeared during the Tertiary,
reached their maximum diversity during the
Quaternary,
and have declined slightly since then

5
Increasingly Familiar

Following the Mesozoic extinctions,
marine invertebrates diversified
giving rise to the present-day familiar marine
fauna
Overall, we can think of the Cenozoic Era
as a time during which Earth's flora and fauna
became increasingly familiar
Cenozoic life history for invertebrates
as well as vertebrates, especially mammals,
is better known that it is for any previous era,
because Cenozoic sedimentary rocks in many areas
are easily accessible at or near the surface

6
Good Fossil Records

Cenozoic rocks are especially common
in western North America,
although they are also found
along the Gulf and Atlantic coasts
Many mammals familiar now,
such as horses, rhinoceroses, rodents, rabbits,
and camels,
have very good fossil records
Indeed, these animals have left so many fossils
that they fill large storage rooms
in museums, and even casual fossil collectors
can find at least parts of them with little
difficulty

7
Marine Invertebrates and Phytoplankton

The Cenozoic marine ecosystem
was populated mostly
by those plants, animals,
and single-cell organisms
that survived the terminal Mesozoic extinction
Gone were the ammonites, rudists,
and most of the planktonic foraminifera
Especially prolific Cenozoic invertebrates
were the foraminifera, radiolarians, corals,
bryozoans, mollusks, and echinoids

8
More Provincial

The marine invertebrate community
in general became more provincial
during the Cenozoic
because of changing ocean currents
and latitudinal temperature gradients
In addition, the Cenozoic marine invertebrate
faunas
became more familiar in appearance
Entire families of phytoplankton
became extinct at the end of the Cretaceous

9
Species Diversified

Only a few species in each major group
survived into the Tertiary
These species diversified and expanded
during the Cenozoic,
perhaps because
of decreased competitive pressures
Coccolithophores, diatoms, and dinoflagellates
all recovered from
their Late Cretaceous reduction in numbers
to flourish during the Cenozoic

10
Diatoms

Diatoms were particularly abundant
during the Miocene, probably
because of increased volcanism during this time
Volcanic ash provided
increased dissolved silica in seawater
which diatoms used to construct their skeletons
Massive Miocene diatomite
is present in several western States

11
CoralsReef Builders Again

Corals were perhaps the main beneficiary
of the Mesozoic extinctions
Having relinquished their reef-building role
to rudists during the mid-Cretaceous,
corals again became the dominant reef builders
They formed extensive reefs
in the warm waters of the Cenozoic oceans
and were especially prolific in the Caribbean
and Indo-Pacific regions

12
Changing Climatic Patterns

Changing climatic patterns
accompanied by shifting plant distributions
characterize the Tertiary
During the Paleocene and Eocene,
mean annual temperatures were high,
abundant precipitation fell,
and tropical to semitropical forests
covered much of North America

13
Leaf Structure

Leaf structure is a good climatic indicator
For instance, leaves with entire or smooth
margins,

many with pointed drip-tips,
are found mostly in areas with abundant rainfall
and high annual temperatures
Smaller leaves with incised margins
are more typical of cooler, less humid regions

14
Late Paleocene Thermal Maximum

Seafloor sediments and geochemical evidence
indicate that about 55 million years ago
an abrupt warming trend took place
During this time,
known as the Late Paleocene Thermal Maximum,
large-scale oceanic circulation was disrupted
so that heat transfer from equatorial regions
to the poles diminished or ceased
As a result,
deep oceanic water became warmer,
resulting in extinctions
of many deep-water foraminifera

15
Major Climatic Change

A major climatic change took place at the end of
the Eocene

when mean annual temperatures
dropped as much as 7 degrees C
in about 3 million years

16
Decrease in Precipitation

A general decrease in precipitation
over the last 25 million years
took place in the mid continent region
of North America
As the climate became drier,
the vast forests of the Oligocene
gave way first to savanna conditions
grasslands with scattered trees
and finally to steppe environments
short-grass prairie of the desert margin

17
Cenozoic Birds

Birds today are diverse and numerous,
making them the most easily observed vertebrates
But the first members
of many of the living orders, including
owls, hawks, ducks, penguins, and vultures,
evolved during the Early Tertiary
Beginning during the Miocene
a marked increase in the variety of songbirds
took place, and by 5 to 10 million years ago
many of the existing genera of birds were present

18
Birds Vary Considerably

Today, birds vary considerably
in habitat, adaptations, and size,
although none are very heavy
Some are seed eaters,
whereas others consume insects, grubs, and worms,
the birds of prey are predators,
and some, such as vultures, eat carrion
Nevertheless, their basic skeletal structure
has remained remarkable constant
throughout the Cenozoic

19
Diatryma

Restoration of Diatryma,
which lived during the Paleocene and Eocene
in North America and Europe

20
Fliers

Large flightless birds still exist
in Africa, South America, and Australia.
They are truly remarkable creatures,
but the real success among birds belongs to the
fliers
Even though few skeletal modifications
occurred during the Cenozoic,
a bewildering array of adaptive types arose
If number of species and habitats occupied
is any measure of success,
birds have certainly been
at least as successful as mammals

21
Mammal Diversification

With the demise of dinosaurs and their relatives,
mammals quickly exploited the adaptive
opportunities,
beginning a remarkable diversification
that continued throughout the Cenozoic Era
The Age of Mammals had begun

22
Mammal Teeth

In fact, mammal teeth
not only differ from front to back of the mouth,
but they also differ among
various mammalian orders
and even among genera and species
This is especially true of the chewing teeth,
the premolars and molars
A single chewing tooth is commonly enough
to identify the genus from which it came

23
South American Marsupials

However, they were also quite widespread
in South America until only
a few millions of years ago
Most South American marsupials died out
when a land connection was established
between the Americas
and placental mammals migrated south
Now the only marsupials (pouch)
outside Australia and some nearby islands
are various species of opossums

24
Placenta

Like marsupials, placental mammals give birth to
live young,
but their reproductive method differs
in important details
In placentals, the amnion of the amniote

has fused with the walls of the uterus,
forming a placenta

25
Mammals

Several orders of mammals existed
during the Mesozoic
but most placental mammals
diversified during the Paleocene and Eocene
epochs
Among the living orders of mammals
all are placentals except for
the monotremes and marsupials

Bold lines are actual geologic ranges thinner
lines are inferred branching
26
Only Vaguely Familiar

Surely we would know they were mammals
and some would be at least vaguely familiar,
but the ancestors of
horses, camels, elephants, and rhinoceroses
bore little resemblance
to their living descendants
Furthermore, some mammals,
such as the giant uintatheres,
would be totally unfamiliar

27
Uintatheres

Scene from the Eocene
showing the rhinoceros-sized mammals
known as uintatheres
They had three pairs
of bony protuberances on the skull
and saberlike upper canine teeth

28
Arsinoitherium

Skull of Arsinoitherium
a rhinoceros to elephant-sized
Early Oligocene animal
with hollow horns more than 0.5 m long

29
Megaloceros

Giant deer Megaloceros giganteus
commonly called Irish Elk
that lived in Europe and Asia during the
Pleistocene
Large males had antler spreads of 3.5 m

30
Increasingly Familiar

As we finish our hypothetical trip
through the Cenozoic,
we can conclude
it was a time
during which the world's mammalian fauna
became increasingly familiar

31
Small Mammals

What do insectivores, rodents, rabbits and bats
have in common?
All are placental mammals
and thus share a common ancestor,
but the main reason for considering them together
is that most are small
and have adapted to the microhabitats
unavailable to larger mammals
In the case of bats,
they are the only mammals capable of flight

32
An Animal Like an Insectivore Gave Rise to
Placental Mammals

As you would expect
from the order name Insectivora,
members of this group,
today's shrews, moles, and hedgehogs,
eat insects
Insectivores have probably not changed much
since they appeared during the Late Cretaceous
In fact, an insectivore-like creature
very likely lies at the base
of the great diversification of placental mammals

33
Saber-Toothed Cats

One of the most remarkable developments in cats
was the evolution of huge canines
in the saber-toothed cats
Saber-toothed cats existed throughout
most of the Cenozoic Era
and are particularly well known
from Pleistocene-aged deposits

34
Carnivores distinctive Are Less Common

Fossils of carnivorous mammals
are not nearly as common as those
of many other mammals
Why should this be so?
First, in populations
of warm-blooded (endothermic) animals,
carnivores constitute no more than 5
of the total population, usually less

35
Carnivores Are Solitary Animals

Second, many, but not all,
carnivores are solitary animals,
so the chance of large numbers
of them being preserved together is remote
Nevertheless, fossil carnivores
are common enough for us
to piece together
their overall evolutionary relationships
with some confidence

36
Carnivores Began to Diversify

The order Carnivora began to diversify
when two distinct lines evolved
from creodonts and miacids during the Paleocene
Both had well-developed
canines and carnassials,
but they were rather short-limbed and flat-footed
Certainly they were not very fast
but neither was their prey

37
Carnivora
The creodont branch became extinct by Miocene
time, so need not concern us further, but the
other branch evolving from miacids led to all
existing carnivorous mammals

Relationships among some carnivores

38
Cats, Hyenas and Dogs

Nevertheless, the fossil record
and studies of living animals
clearly indicate hyenas

are more closely related to cats and mongooses

Their similarity to dogs

is another example of convergent evolution

39
The Ungulates or Hoofed Mammals

The term ungulate is an informal one
referring to several groups of living and extinct
mammals
Actually, it refers to having hoofs,
but not all ungulates do have hoofs
However, the most numerous ungulates
are indeed hoofed mammals belonging
to the orders Artiodactyla and Perissodactyla

40
Artiodactyla and Perissodactyla

The artiodactyls,
commonly called even-toed hoofed mammals,
are the most diverse and numerous
with about 170 living species
of cattle, goats, sheep, swine, antelope, deer,
giraffes, hippopotamuses, camels, and several
others
In marked contrast, the perissodactyls
or odd-toed hoofed mammals,
have only 16 existing species
of horses, rhinoceroses, and tapirs

41
Defining Characteristics of Hoofed Mammals

During the Early Tertiary, though,
perissodactyls
were more abundant than artiodactyls
Some defining characteristics
of these groups of hoofed mammals
are the number of toes
and how the animal's weight is borne on the toes
Their teeth are also distinctive

42
Toes of Hoofed Mammals

Perissodactyls have one or three functional toes
whereas artiodactyls have two or four toes
in perissodactyls the weight is borne on the
third toe
artiodactyls walk on toes two and four

43
Perissodactyls

Perissodactyls have one or three toes,
although a few fossil species
retained four toes on their forefeet
Nevertheless, their weight is
borne on a axis passing through the third toe
Even today's horses
have vestigial side toes
and rarely are they born with three toes

44
Size for Protection

Size alone is adequate protection
in some very large species such as rhinoceroses
In contrast to the long, slender limbs
of horses, antelope, deer, and so on,
these animals
have developed massive, weight-supporting legs

45
Low- and High-Crowned Teeth

Once grasses had evolved,
many hoofed mammals became grazers
and developed high-crowned, abrasion-resistant
teeth

Low-crowned teeth
are typical of many mammals with varied diets

High-crowned, cement-covered chewing teeth
are adapted for grazing

46
Relationships Among Artiodactyls

Relationships among the living artiodactyls

and some extinct ones

The oldest known artiodactyls were Early Eocene
rabbit-sized animals that differed little from
their ancestors Yet these rather small creatures
were ancestral to the myriad living and several
extinct families of even-toed hoofed mammals
47
Extinct Artiodactyls

Among the extinct families
are the rather piglike oreodonts

so common in North America
until their extinction during the Pliocene
and the peculiar protoceratids
with forked horns on their snouts

48
Camel Evolution

Most camel evolution
took place in North America,
but during the Pliocene they migrated
to Asia and South America,
where the only living species exist now
North American camels
went extinct near the end
of the Pleistocene Epoch

49
Bovidae

Artiodactyls in general,
both species and individuals
are quite numerous and among them
the family Bovidae
is by far the most diverse, with dozens of
species
of cattle, bison, sheep, goats, and antelope
This family did not appear until the Miocene,
but most of its diversification
took place during Pliocene time
on the northern continents

50
Bovids in North America

Bovids are now most numerous
in Africa and southern Asia
North America still has its share of bovids
such as bighorn sheep and mountain goats,
but the most common ones
during the Cenozoic were bison,
migrants from Asia,
the pronghorn, and oreodonts,
all of which roamed the western interior
in vast herds

51
Artiodactyls

Most artiodactyls are ruminants, that is,
cud-chewing animals
the major exceptions being pigs
and their relatives the peccaries and hippos

52
Predicted by the Theory of Evolution

This kind of fossil evidence
is exactly what we expect
if the theory of evolution is valid
Recall from our discussion of the theory of
evolution
If we examine the fossil record
of presumably related organisms
we should find that they were quite similar
when they diverged from a common ancestor
but became increasingly different
as their divergence continued.

53
Artiodactyls Cladogram

Fossil evidence indicates a close tie
between ancestors of the artiodactyls

54
Fossil Record of Horses

With the possible exception of camels,
probably no group of mammals
has a better fossil record than do horses
Indeed, horse fossils are so common,
especially in North America
where most of their evolution took place,
that their overall history
and evolutionary trends are quite well known

55
Evolution of Horses

Summary chart
showing genera of horses
During the Oligocene
two separate lines emerged
one leading to three-toed browsers

and the other to one-toed grazers

including the present-day horses

56
Horse Evolution

Some evolutionary trends in horses
include an increase in size
lengthening of the limbs
reduction in the number of toes
and development of high-crowned teeth
with complex chewing surfaces

57
Earliest Member of the Horse Family

The earliest member
of the horse family (family Equidae)
is the fox-sized animal known as Hyracotherium
This small forest-dwelling animal
had four-toed forefeet and three-toed hind feet,
but each toe was covered by a small hoof
Otherwise it possessed
few of the features of present-day horses

58
Hyracotheriums Link to Horses

So how can we be sure Hyracotherium belongs
to the family Equidae at all?
Horse evolution
was a complex, branching affair,
with numerous genera and species
existing at various times during the Cenozoic
Nevertheless, their exceptional fossil record
clearly shows Hyracotherium is linked
to the present-day horse, Equus,
by a series of animals
possessing intermediate characteristics

59
Horse Evolution Branched

Horse evolution proceeded along two distinct
branches
One led to three-toed browsing horses,
all now extinct,
and the other led to three-toed grazing horses
and finally to one-toed grazers
The appearance of grazing horses,
with high-crowned chewing teeth
coincided with the evolution and spread of
grasses
during the Miocene

60
Elephants

Phylogeny of present-day elephants
and some of their relatives
Trends were
increased size and development of large tusks
and along proboscis

Several fossil elephants are not shown

61
Elephant Tusks

By Oligocene time, elephants existed
that showed the trends toward large size,
and that had developed a long proboscis
and large tusks
Incidentally, elephant tusks
are enlarged incisors,
not canine teeth as many people think
Most elephants developed tusks
in the upper jaw only,
but a few had them in both jaws,
and one, the deinotheres, had only lower tusks

62
Mastodons and Mammoths

The most familiar elephants,
other than living ones,
are the extinct mastodons and mammoths
Mastodons evolved in Africa,
but from Miocene to Pleistocene time
they spread
over the Northern Hemisphere continents
and one genus even reached South America
These large browsing animals
died out only a few thousands of years ago
During the Pliocene and Pleistocene
mammoths and living elephants diverged

63
Mammoths

Most mammoths were no larger
than elephants today,
but they had the largest tusks of any elephant
In fact, mammoth tusks are common enough
in Siberia that they have been
and continue to be a source of ivory
Until their extinction
near the end of the Pleistocene mammoths lived
on all Northern Hemisphere continents
as well as in India and Africa

64
Giant Aquatic Mammals Whales

Our fascination with huge dinosaurs
should not overshadow the fact that
by far the largest animal ever is alive today
At more than 30 m long
and weighing an estimated 130 metric tons
blue whales greatly exceed the size of any other
living thing,
except some plants such as redwood trees
But not all whales are large

65
Land-Dwelling Ancestors

Fossils discovered in Middle Eocene rocks
in Pakistan indicate that their land-dwelling
ancestors
were among the artiodactyls,
but some paleontologists think
the ancestors were the wolf-sized,
meat-eating mammals called mesonychids

66
Whale Cladogram

Cladogram showing the relationships
among some fossil and living whales
and their land-dwelling ancestors
Pakicetus had well-developed hind limbs,
but only vestiges remain
in Protocetus
and Basilosaurus

67
Mammals of the Ice Age

The most remarkable aspect
of the Pleistocene mammalian fauna
is that so many very large species existed
Mastodons, mammoths, giant bison,
huge ground sloths, immense camels,
and beavers 2 m tall
at the shoulder were present in North America
South America had its share of giants, too,
especially sloths and glyptodonts

68
Cooler ConditionsLarger Sizes

Of course, many smaller mammal species
also existed,
but one obvious trend among Pleistocene mammals
was large body size
Perhaps this was an adaptation
to the cooler conditions
that prevailed during that time
Large animals have less surface area
compared to their volume
and thus retain heat more effectively
than do smaller animals

69
Pliocene and Pleistocene Mammals of Florida

Among the diverse Pliocene and Pleistocene
mammals of Florida were
6-m-long giant sloths

armored animals known as glyptodonts
that weighted more than 2 metric tons

70
La Brea Tar Pits

At the La Brea tar pits
the tar is naturally formed asphalt,
whereas true tar is a product manufactured from
peat or coal
at least 200 kinds of animals were found trapped
in the sticky residue
where liquid petroleum seeped
out at the surface and then evaporated
Many of the fossils of are carnivores,
especially dire wolves and saber-toothed cats
that gathered to dine on various animals
that became mired in the tar

71
Pleistocene La Brea Tar Pits

Mural by Charles R. Knight
shows Late Pleistocene animals La Brea, California

A herd of mammoths is visible in the distance
A giant ground sloth is trapped in tar
while giant vultures and saber-tooth cats wait
nearby
72
Pleistocene Extinctions