Chapter 18
Life of the Cenozoic Era
main points….
1. Angiosperms diversified, along with invertebrates
2. 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.
Cenozoic Life History
• The Cenozoic was the time during which
– Earth’s 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
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
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
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
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
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
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
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
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
Corals—Reef 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
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
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
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
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
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
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
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
Diatryma
• Restoration of
Diatryma,
– which lived
during the
Paleocene and
Eocene
– in North
America and
Europe
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
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
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
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
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
Mammals
• Several orders of
mammals existed
– during the Mesozoic
– but most placental
mammals
– diversified during the
Paleocene and Eocene
epochs
Bold
lines are
actual
• Among the living
geologic
orders of mammals
ranges
– all are placentals except thinner
for
lines are
– the monotremes and
inferred
marsupials
branching
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
Uintatheres
• Scene from the Eocene
– showing the rhinocerossized mammals
– known as uintatheres
• They had three pairs
– of bony protuberances
on the skull
– and saberlike upper
canine teeth
Arsinoitherium
• Skull of
Arsinoitherium
– a rhinoceros to
elephant-sized
– Early Oligocene
animal
– with hollow horns
more than 0.5 m
long
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
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
Artiodactyls
• Most artiodactyls are ruminants, that is, cud-chewing
animals
– the major exceptions being pigs
– and their relatives the peccaries and hippos
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.”
Artiodactyls Cladogram
• Fossil evidence indicates a close tie
– between ancestors of the artiodactyls
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
Evolution of Horses
• Summary chart
– showing genera of
horses
• During the Oligocene
– two separate lines
emerged
– one leading to threetoed browsers
– and the other to onetoed grazers
– including the presentday horses
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
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
Hyracotherium’s 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
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
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
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
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
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
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
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
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
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
Cooler Conditions—Larger 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
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
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
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
while giant vultures
A giant ground sloth is trapped in tar
and saber-tooth cats
wait nearby
Pleistocene Extinctions
• Extinctions have occurred continually
–
–
–
–
during life history,
but at times of mass extinctions
Earth's biotic diversity sharply declined,
as at the ends of the Paleozoic and Mesozoic eras
• In marked contrast,
–
–
–
–
–
the Pleistocene extinctions were rather modest,
but they did have a profound effect
on genera of large terrestrial mammals,
those weighing more than 40 kg,
and some large flightless birds
Extinctions
• The facts just discussed bring up three
questions:
(1) What caused extinctions?
(2) Why did these extinctions eliminate mostly large
mammals?
(3) Why were extinctions more severe in Australia
and the Americas?
• No completely satisfactory explanation exists,
– but two competing hypotheses are currently being
debated
Extinction Hypotheses
• One hypothesis holds
– that rapid climatic changes
– at the end of the Pleistocene
– caused extinctions, glaciers withdrew…
• whereas another hypothesis
• called prehistoric overkill
– holds that human hunters were responsible
South America
• South America was an island continent
– from the Late Cretaceous
– until a land connection with North America
– was established about 5 million years ago
• The South American mammalian fauna
• at that time,
– consisted of various marsupials
– and several orders of placental mammals
– that lived nowhere else in the world
• These animals thrived in isolation
– and showed remarkable convergence
– with North American placentals
Isthmus of Panama
• When the Isthmus of Panama formed,
– however, migrants from North America
– soon replaced most of the indigenous
– South American mammals
• Among the marsupials
– only opossums survived,
– and most of the placentals also died out
• The land connection allowed migrations
– in both directions,
– and several South American mammals
– successfully migrated northward
Migrations between Americas
• Several
mammals
successfully
migrated and
occupied
North
America
• Many types •
of placental
mammals
migrated
south
Many South
American
mammals
soon became
extinct
Marsupials
• Most of the living species of marsupials
– are restricted to the Australian region
• Marsupials occupied Australia
– before its complete separation from Gondwana,
– but apparently placentals,
– other than bats and a few rodents, never did
Primates Evolved
• Primates might have evolved
– by Late Cretaceous time,
– but they were undoubtedly present by the Paleocene
• Small Paleocene primates
– closely resembled their contemporaries,
– the shrew-like insectivores
• By the Eocene, though,
– larger primates had evolved
Primate Evolution
• Lemurs and tarsiers
– that resemble their present descendants
– lived in Asia and North America during the Eocene
• By Oligocene time
– primitive New World and Old World monkeys
– had developed
– in South America and Africa, respectively
• The Hominoids,
– the group that includes apes and humans,
– evolved during the Miocene
Summary
• The marine invertebrate groups
– that survived the Mesozoic extinctions
– diversified throughout the Cenozoic
• Bivalves, gastropods, corals,
– and various kinds of phytoplankton
– such as foraminifera proliferated
• During much of the Early Cenozoic,
–
–
–
–
–
subtropical and tropical forests
covered North America,
but the climate became drier
by Oligocene and Miocene time,
especially in the midcontinent region
Summary
• Birds belonging to living orders and families
– evolved during the Early Tertiary Period
• Large, flightless predatory birds
– of the Early Tertiary eventually gave way
– to mammalian predators
• The evolutionary history of mammals
–
–
–
–
is better known than it is
for other classes of vertebrates
because they have a good fossil record
and their teeth are so distinctive
Summary
• Egg-laying mammals (monotremes) and
marsupials
–
–
–
–
exist mostly in the Australian region,
but the placental mammals,
by far the most common mammals,
owe their success to their method of reproduction
• All placental and marsupial mammals
– descended from shrewlike ancestors
– that existed from Late Cretaceous to Early
Tertiary time
Summary
• Small mammals
– such as insectivores, rodents, and rabbits
– occupy the microhabitats unavailable
– to larger mammals
• Bats, the only flying mammals,
– have forelimbs modified into wings
– but otherwise differ little from their ancestors
Summary
• Most carnivorous mammals
–
–
–
–
–
have well-developed canine teeth
and specialized shearing teeth,
although some aquatic carnivores
such as seals have peglike teeth
all of which look much the same
• The most common ungulates
– are the even-toed hoofed mammals (artiodactyls)
– and odd-toed hoofed mammals (perissodactyls),
– both of which evolved during the Eocene
Summary
• Many ungulates show evolutionary trends
– such as molarization of the premolars
– as well as lengthening of the legs for speed
• During the Early Cenozoic,
–
–
–
–
–
perissodactyls were more common
than artiodactyls
but now their 16 living species
constitutes only about 10%
of the world's hoofed mammal fauna
Summary
• Although present-day Equus
–
–
–
–
–
–
differs considerably
from the oldest known member
of the horse family, Hyracotherium,
an excellent fossil record
shows a continuous series
of animals linking the two
• Even though horses, rhinoceroses, and tapirs
–
–
–
–
–
as well as the extinct titanotheres and chalicotheres
do not closely resemble one another,
fossils and studies of living animals
show that they diverged
from a common ancestor during the Eocene
Summary
• The fossil record for whales
– is now complete enough to verify
– that they evolved from land-dwelling ancestors
• Elephants evolved from rather small ancestors,
– became quite diverse and abundant,
– especially on the Northern Hemisphere continents,
– and then dwindled to only two living species
Summary
• Horses, camels, elephants, and other mammals
–
–
–
–
spread across the northern continents
during the Cenozoic
because land connections existed
between those landmasses at various times
• South America was isolated
– during most of the Cenozoic
– and its mammalian fauna was unique
Summary
• A land connection was established
–
–
–
–
between the America's
during the Late Cenozoic
and migrations in both directions
took place between the continents
• One important evolutionary trend
– in Pleistocene mammals and some birds
– was toward giantism
• Many of these large species died out
– beginning about 40,000 years ago
Summary
• Changes in climate and prehistoric overkill
– are the two hypotheses
– explaining Pleistocene extinctions
Cenozoic Biota
• Recall that when Earth formed
–
–
–
–
it was hot, barren, and waterless,
the atmosphere was quite noxious,
and early organisms were single celled bacteria
or their precursors
• By Cenozoic time, though,
–
–
–
–
Earth was taking on its present-day appearance
and its biota continued to evolve
as more and more familiar types
of plants and animals appeared
John Day Fossil Restoration
• The dryer conditions that prevailed
– when the John Day Formation was deposited
Three-toed horses
Sabertooth catlike
piglike entelodonts
animal
rhinoceros
small deerlike animals
oreodonts
John Day Fossils Discovered
• Fossil mammals and plants
– were first collected here
– by U.S. cavalry soldiers during the Civil War
(1861-1865)
– and scientists have studied these fossils ever since,
– giving us a good idea of what life and the climate
– were like in central Oregon millions of years ago
Plant leaves as
Climatic Indicators
• Thus fossil floras with high percentages
– of smooth-margin leaves with drip-tips
– indicate the climate
– was wet and warm
Recently Birds’ Diversity
Decreased
• Birds adapted to numerous habitats
– and continued to diversify into the Pleistocene,
– but since then their diversity
– has decreased slightly
Mammals
Mammals
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
Rabbits
• Rabbits (order Lagomorpha)
– superficially resemble rodents
– but differ from them
– in several anatomic details
• Furthermore, since they arose
– from a common ancestor during the Paleocene
– rabbits and rodents
– have had an independent evolutionary history
• Like rodents, rabbits are gnawing animals,
– although details of their gnawing teeth differ
Powerful Hind Limbs
• The development of long, powerful hind limbs
– for hopping and speed
– is the most obvious evolutionary trend
– in rabbits
Aquatic Carnivores
• Unfortunately the ancestry of aquatic carnivores
– is less well known
– than for other families of carnivores
• Aquatic adaptations include
– a somewhat streamlined body,
– a layer of blubber for insulation,
– and limbs modified into paddles
• Most are fish-eaters
– and have rather simple, single-cusped teeth,
– except walruses
– which have flattened teeth for crushing shells
Artiodactyls
• Artiodactyls have either two or four toes,
– and their weight is borne along an axis
– that passes between the third and fourth digits
• For those artiodactyls with two toes,
– such as today's swine and deer,
– the first, second, and fifth digits
– have been lost or remain only as vestiges
Hoofed Herbivores
• All artiodactyls and perissodactyls
– are herbivorous animals
– with their chewing teeth,
• premolars and molars,
– modified for a diet of vegetation
• One evolutionary trend in these animals
–
–
–
–
–
was molarization,
a change in the premolars
so that they are more like molars,
thus providing
a continuous row of grinding teeth
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
Pliocene
– a rodent
– a rabbit
– Merycodus, an
extinct
pronghorn
– Synthetoceras, a
hoofed mammal
with a horn on its
snout
– Pliohippus, a
one-toed grazing
horse
John Day Fossil Beds
• One such area,
– John Day Fossil Beds National Monument,
– consists of three widely separated units in central
Oregon
• Among its several attractions
– is its truly inspiring scenery
– of reddish, pink, greenish, white, yellow, and black
rocks
– and its fossil mammals dating
– from 54 million to 6 million years ago
Since Paleocene
• With the exception of bats,
–
–
–
–
all of these small mammals
have been integral parts
of the world's mammalian fauna
since at least Paleocene time
Pliocene and Pleistocene
Mammals of Florida
– 6-m-long giant sloths
– armored animals known as
glyptodonts
A Brief History of the Primates
• The order Primates includes
– the “lower primates”
• tarsiers, lemurs, and lorises,
– and the living monkeys, apes, and humans,
– collectively referred to as “higher primates”
• We will tell much of the primate story later
– when we consider human evolution,
– so here we will be brief
Not More Complex
• So contrary to popular belief,
– evolutionary processes do not necessarily
– yield more and more complex structures
• Also, remember that some Mesozoic
mammals
– still had reptile features, such as jaw–skull joints
– and the distinction
– between cynodonts and the earliest mammals
– is difficult to make
John Day Fossil Restoration
• Restoration of Clarno Formation fossils
– from Eocene age rocks in John Day Fossil Beds
National Monument Oregon
– The Climate at this time was subtropical
– and the lush forests of the region were occupied by
early rhinoceroses
tapirs
Titanotheres standing 2.5m high at the shoulder
ancient horses
carnivores
Cenozoic Foraminifera
• Benthonic
foraminifera of the
Cenozoic Era
– Lenticulina mexicana
– Eocene, Louisiana
Cenozoic Foraminifera
• A planktonic
form
– Globigerinoides
fistulosus
– Pleistocene,
– South Pacific
Ocean
Other Suspension Feeders
• Other suspension feeders
– such as bryozoans and crinoids
– were also abundant and successful
– during the Tertiary as well as the Quaternary
• Bryozoans, in particular, were very abundant
• Perhaps the least important
– of the Cenozoic marine invertebrates
– were brachiopods,
– with fewer than 60 genera surviving today
Mollusks
• Just as during the Mesozoic,
–
–
–
–
bivalves and gastropods
were two of the major groups
of marine invertebrates during the Tertiary,
and they had a markedly modem appearance
• After the extinction of ammonites and
belemnites
–
–
–
–
at the end of the Cretaceous,
the Cenozoic cephalopod fauna
consisted of nautiloids and shell-less cephalopods
such as squids and octopuses
Echinoids
• Echinoids continued their expansion
– in the infaunal
habitat
– and were
particularly
prolific
– during the Tertiary
• New forms such
as this sand dollar
– evolved during
this time
– from biscuitshaped ancestors
Paleocene Flora
• Paleocene rocks
– in North America's western interior
– have fossil ferns and palms,
– both indicating a warm subtropical climate
• In a recently discovered Paleocene flora
–
–
–
–
in Colorado
with about 100 species of trees,
nearly 70 percent of the leaves
had smooth margins and many had drip tips
• This range of diversity is much like
– that found in today's rain forests
Release of Methane
• Some scientists think
–
–
–
–
–
–
–
that this deep, warm oceanic water
released methane
from seafloor methane hydrates,
contributing a greenhouse gas
to the atmosphere
and either causing or encouraging
the temperature increase at this time
Subtropical Conditions
• Subtropical conditions persisted
– into the Eocene in North America,
– probably the warmest of all the Tertiary epochs
• Fossil plants in the Eocene John Day Beds in
Oregon
– include ferns, figs, and laurels,
– all of which today live only in
– the humid parts of Mexico and Central America
Warm Eocene Climate
• Yellowstone National Park in Wyoming
–
–
–
–
has a temperate climate now
with warm dry summers and cold snowy winters,
certainly not an area where one would expect
avocado, magnolia, and laurel trees to grow
• Yet their presence there
– during the Eocene indicates the area
– had a considerably warmer climate
– than it does now
Adaptations for Flying
• Given that birds evolved from a creature very
much like Archaeopteryx
– this uniformity is
not surprising
– because
adaptations for
flying
– impose limitations
– on variations in
structure
Diatryma and Related Genera
• Its massive, short legs
– indicate that Diatryma was not very fast,
– but neither were the early mammals it preyed on
• This extraordinary bird and related genera
–
–
–
–
–
were widespread in North America and Europe
during the Early Tertiary,
and in South America
they were the dominant predators
until about 25 million years ago
• Eventually, they died out,
– being replaced by carnivorous mammals
Easier to Study Cenozoic Fossils
• We have already mentioned
–
–
–
–
–
that Cenozoic deposits are easily accessible
at or near the surface,
and overall they show fewer changes
resulting from metamorphism and deformation
when compared with older rocks
• In addition, because mammals
– have teeth fully differentiated into various types,
– they are easier to identify and classify
– than members of the other classes of vertebrates
Class Mammalia
• All warm-blooded vertebrates
– with hair and mammary glands
– are members of the class Mammalia,
– which includes two fundamentally different kinds of
mammals
– the prototheria and the theria (or eutheria)
• The prototheria include some extinct animals
– but the only living ones are the monotremes
• order Monotremata or egg-laying mammals
– the platypus and spiny anteater of the Australian
region
Therian Mammals
• Therians, in contrast, include all mammals
– that give birth to live young
– such as marsupial mammals
• order Marsupialia,
• commonly called “pouched mammals”
– and the placental mammals
• with about 18 living orders
Marsupial Mammals
• Marsupial mammals give birth to live young,
– which are born in a very immature,
– almost embryonic condition
– and then undergo further development
– in the mother's pouch
• Marsupials probably migrated to Australia,
– the only area in which they are common today,
– via Antarctica before Pangaea fragmented
completely
Marsupial Placenta Less Efficient
• Nutrients and oxygen flow
– from mother to embryo through the placenta,
– permitting the young to develop
– much more fully before birth
• Actually, marsupials also have a placenta,
– but it is less efficient,
– explaining why their newborn
– are not as fully developed
Success of Placental Mammals
• A measure of the success of placental mammals
– is partially related
– to their method of reproduction
• More than 90% of all mammals,
• fossil and extinct,
– are placentals
• All today's placental mammals
– as well as several extinct groups
– evolved from Late Cretaceous
– and Early Tertiary ancestors
Diversification of Placental
Mammals
• In our following discussion of placental
mammals,
– we emphasize the origin and evolution
– of several of the 18 or so living orders
– and a few extinct ones
• Recall that in Linnaeus's classification scheme
– an order
– consists of one or more related families
Orders Made of Families
• For instance, the families
– Canidae (dogs), Felidae (cats), Ursidae (bears),
– and several others,
– constitute the order Carnivora
• Mammals of one kind or another existed
–
–
–
–
through most of the Mesozoic
along with dinosaurs,
and the Mesozoic was in fact
an important time in their evolution
Moas and Elephant Birds
• Two of the most notable large flightless birds
– were the now extinct moas of New Zealand
– and elephant birds of Madagascar
• Moas were up to 3 m tall,
– whereas elephant birds were shorter
– but more massive, weighing up to 500 kg
• more than five times the weight
• of a good sized human
• They are known only
– from Pleistocene-age deposits,
– and both went extinct shortly after
– humans occupied their respective areas
Paleocene Mammals
• However, the Cenozoic,
– commonly referred to as the Age of Mammals,
– was truly the time of mammal diversification
• During the Paleocene Epoch
–
–
–
–
–
several orders of mammals were present,
but some were simply holdovers
from the Mesozoic
or belonged to new but short-lived groups
that have no living descendants
Mostly Small Creatures
• The Paleocene mammalian fauna
– was also made up mostly of small creatures
• By Late Paleocene time, though,
– some rather large mammals were around,
– although giant terrestrial mammals
– did not appear until the Eocene
• Recall that some
– very large, flightless, predatory birds were present,
– but even these were not giants
Mammalian Orders by the Eocene
• Many mammalian orders that evolved
–
–
–
–
during the Paleocene died out,
but of the several
that first appeared during the Eocene
only one has become extinct
• Thus by Eocene time
– many of the mammalian orders
– existing now were present
• Yet if we could go back for a visit
– we would not recognize most of these animals
Archaic Paleocene Mammals
Died Out
• Warm, humid climates persisted
– throughout the Paleocene and Eocene,
– but by Oligocene time
– drier and cooler conditions prevailed
• Most of the archaic Paleocene mammals
– as well as several groups
– that originated during the Eocene
– had died out by this time
• The uintatheres and
– large, rhinoceros-like titanotheres
– went extinct
Other Groups Died Out
• In addition, several smaller groups of mammals
–
–
–
–
–
–
suffered extinctions, including
several types of herbivores
loosely united as condylarths,
carnivorous mammals known as creodonts,
most of the remaining multituburculates,
and some primates
• All in all, this was a time
– of considerable biotic change
Oligocene
• By Oligocene time,
–
–
–
–
most of the existing mammalian orders
were present,
but they continued to diversify
as more and more familiar genera evolved
• If we were to encounter some of these animals
–
–
–
–
we might think them a bit odd,
but we would have little difficulty recognizing
rhinoceroses, although some were hornless,
elephants, horses, rodents, and many others
Mammals of the Tertiary Period
• We know mammals evolved
– from mammal-like reptiles
– called cynodonts
– during the Late Triassic,
• and diversified during the Cenozoic,
– eventually giving rise
– to the present-day mammalian fauna
• Now more than 4000 species exists,
– ranging from tiny shrews to
– giants such as whales and elephants
Most Mammals Are Quite Small
• When one mentions the term mammal,
– what immediately comes to mind are
– horses, pigs, cattle, deer, dogs, cats, and so on,
– but most often we do not think much about small
mammals,
– rodents, shrews, rabbits, and bats
• Yet most mammals are quite small,
– weighing less than 1 kg
Rodents Eat Almost Anything
• Rodents evolved during the Paleocene
– and not only have diversified
– into numerous species
– but also have adapted
– to a wide range of habitats
• One reason for their phenomenal success
– is that they can eat almost anything
Bat Wings
• Unlike pterosaurs and
birds,
– bats use a modification
of the hand
– in which four long
fingers
– support their wings
Jaws of Large Cats
• This present-day skull and jaw of a large cat
– show the specialized sharp-crested shearing teeth
– of carnivorous mammals
• The canine teeth are also large,
– but several Cenozoic saber-tooth cats
– had huge canine teeth
• the one shown here is the Oligocene Eusmilus
specialized sharp-crested shearing
teeth called carnassials
huge canine
saber tooth
Cenozoic Foraminifera
• Benthonic
foraminifera of the
Cenozoic Era
– Cibicides americanus
– Early Miocene,
California
Plant leaves as Climatic Indicators
• Climatic trends for four areas in North
America
– based on
the
percentages
of plant
species
– with entire
margin
leaves
Rodents
• More than 40% of all existing mammal species
– are rodents (order Rodentia),
– most of which are very small
• A few, though, including
–
–
–
–
beavers and the capybara of South America,
are sizable animals,
the latter measuring more than 1 m long
and weighing in excess of 45 kg
Fossil Bats
• The oldest fossil bat (order Chiroptera)
– comes from the Eocene-age Green River Formation
of Wyoming,
– but well-preserved specimens are known
– from several other areas, too
• Apart from having forelimbs modified into
wings,
– bats differ little from their immediate ancestors
– among the insectivores
• Indeed, with the exception of wings
– they closely resemble living shrews
Carnivore Specialties
• Nevertheless, most carnivores
– have well-developed, sharp, pointed canine teeth
– and specialized shearing teeth
– known as carnassials for slicing meat
• Some land-dwelling carnivores
– depend on speed, agility, and intelligence
– to chase down prey,
– but others employ different tactics
• Badgers, for instance, are not very fast
– they dig prey from burrows,
– and some small cats depend on
– stealth and pouncing to catch their meals
Aquatic
Carnivores
• Seals, sea
lions, and
walruses
– are most
closely
related to
bears
Fewer Bony Elements
• In addition, these speedy runners
– have fewer bony elements in the feet,
– mostly because they have fewer toes
• Not all hoofed mammals
– are long-limbed, speedy runners
• Some are quite small
– and dart into heavy vegetation
– or a hole in the ground
– when threatened by predators
Artiodactyls More Effective
• Perhaps the fact that artiodactyls
–
–
–
–
–
use the same resources more effectively
than do perissodactyls
explains why artiodactyls have flourished
and mostly replaced perissodactyls
in the hoofed mammal fauna
Perissodactyls —
Odd-Toed Hoofed Mammals
• As paleontologists trace horses, rhinoceroses,
tapirs,
– and their extinct cousins
– the titanotheres and chalicotheres
– back through the fossil record,
– differentiating one from the other
– becomes increasingly difficult
Perissodactyls Diverged Then
Declined
• These various perissodactyls
–
–
–
–
diverged from Paleocene ancestors,
reached their greatest abundance
during the Oligocene,
and have declined markedly since then
Progressive Trend in the
Development
• Late Eocene and Early Oligocene horses,
–
–
–
–
followed by more recent ones
show a progressive development
of various characteristics
found in present-day Equus
Other Perissodactyls
• The other living perissodactyls,
–
–
–
–
rhinoceroses and tapirs,
increased in size from Early Cenozoic ancestors,
and both became more diverse
and widespread than they are now
• Most rhinoceroses evolved in the Old World,
– but North American rhinoceroses were common
– until they became extinct on this continent
– at the end of the Pleistocene
Chalicotheres
• Chalicotheres,
• although never particularly abundant,
– are interesting though
– because the later members of this family
– were the size of large horses
– but their feet had claws on their feet
– rather than hooves
• The prevailing opinion is that these claws
– were used to hook and pull down branches
Not All Whales Are Large
• Consider, for instance,
– dolphins and porpoises
– both are sizable but hardly giants
• Nevertheless, an important trend
– in whale evolution
– has been increase in body size
Aquatic Mammals
• Several kinds of mammals
– are aquatic or semiaquatic,
– but only sea cows and whales, order Cetacea,
– are so thoroughly aquatic
– that they cannot come out onto land
Eocene whales
• The Early Eocene whale Ambulocetus
–
–
–
–
still had limbs capable of support on land,
whereas Basilosaurus,
a 15-m-long Late Eocene whale,
had only tiny, vestigial rear limbs
• Basilosaurus still had teeth similar
–
–
–
–
–
to those of mesonychids,
and its nostrils were still on the snout,
but it was truly a whale,
although very differently proportioned
from those living now
Baleen and Toothed Whales
• By Oligocene time,
– both presently existing whale groups
• baleen whales and toothed whales
– had evolved
Pleistocene Faunas
• As opposed to fauna of the Paleocene Epoch
–
–
–
–
–
with its archaic mammals,
unfamiliar ancestors of living mammalian orders,
and large predatory birds,
the fauna of the Pleistocene consists
mostly of quite familiar animals
• Even so, their geographic distribution
–
–
–
–
–
might surprise us because
rhinoceroses, elephants, and camels
still lived in North America,
and a few unusual mammals, such as chalicotheres
and the heavily armored glypotodonts, were present
Pleistocene Avian Fauna
• In the avian fauna,
– giant moas were in New Zealand
– and elephant birds were in Madagascar
Frozen Mammals
• Some of the world's best-known fossils
– come from Pleistocene deposits
• Everyone has heard
– of the frozen mammals found in Siberia and Alaska,
– such as mammoths, bison, and a few others
• These extraordinary fossils,
– although very rare,
– provide much more information than most fossils do
Frozen Baby Mammoth
• Frozen baby mammoth found
– in Siberia in 1971,
– 1.15 m long
and 1.0 m
tall,
– had a hairy
coat
Recovered From Permafrost
• Contrary to what you might hear
– in the popular press,
– all of these frozen animals were partly
decomposed,
– none were fresh enough to eat,
– and none were found in blocks of ice or icebergs
• All were recovered
– from permanently frozen ground
– known as permafrost
Lost Genera
• Particularly hard hit were Australia and the
Americas
• In Australia, 15 of the continent's 16 genera
– of large mammals died out,
– North America lost 33 of 45 large-mammal genera,
– and in South America 46 of 58 such genera went
extinct
• In contrast, Europe lost only 7 of 23 such
genera,
– and in Africa south of the Sahara
– only 2 of 44 died out
Climate and Vegetation Changes
• The Arctic region flora changed
–
–
–
–
from a productive herbaceous one
that supported a variety of large mammals,
to a relatively barren water-logged tundra
that supported a far sparser fauna
• The southwestern U.S. region also changed
–
–
–
–
–
from a moist area with numerous lakes,
where saber-toothed cats, giant ground sloths,
and mammoths roamed,
to a semiarid environment
unable to support a diverse large mammalian fauna
Argument Against
the Climatic Hypothesis
• The second argument
– against the climatic hypothesis
– is the apparent lack of correlation
– between extinctions
– and the earlier glacial advances and retreats
– throughout the Pleistocene Epoch
• Previous changes in climate
– were not marked by episodes of mass extinctions
Hunters Concentrate
on Small Animals
• A second problem is that present-day hunters
– concentrate on smaller, abundant,
– and less dangerous animals
• The remains of horses, reindeer,
– and other small animals
– are found in many prehistoric sites in Europe,
– whereas mammoth and woolly rhinoceros remains
– are scarce
Other Arguments
• Finally, few human artifacts
–
–
–
–
are found among the remains of extinct animals
in North and South America,
and there is usually little evidence
that the animals were hunted
• Countering this argument
– is the assertion that the impact
– on the previously un-hunted fauna
– was so swift as to leave little evidence
Intercontinental Migrations
• The mammalian faunas
– of North America, Europe, and northern Asia
– exhibited many similarities
– throughout the Cenozoic
• Even today, Asia and North America
– are only narrowly separated at the Bering Strait,
– which at several times during the Cenozoic formed
– a land corridor across which mammals migrated
Fossils Featured in National Parks
• Dinosaurs are undoubtedly
– the most popular prehistoric creatures,
– but extraordinary concentrations
– of Cenozoic animal and plant fossils
– are featured in several of our national parks
• and monuments
– in Wyoming, Colorado, Nebraska, and South
Dakota
The Age of Mammals Begins
• Mammals coexisted with dinosaurs
–
–
–
–
for more than 100 million years,
yet during this entire time
they were neither abundant nor diverse,
and all were quite small
• Indeed, even at the end of the Cretaceous
– only a few families of mammals existed,
– a situation that was soon to change
Metasequoia
• Well-preserved
leaves of
Metasequoia
(dawn redwood)
– Oligocene-toMiocene John
Day Formation of
Oregon
– These rocks
provide a good
record of the
ancient flora and
fauna of central
Oregon
Diatomite
• Outcrop of diatomite from the Miocene
– Monterey Formation, Newport Lagoon, California
Foraminifera
• The foraminifera were a major component
– of the Cenozoic marine invertebrate community
• Although dominated by relatively small forms,
– it included some exceptionally large forms
– that lived in the warm waters
– of the Cenozoic Tethys Sea
• Shells of these larger forms accumulated
– to form thick limestones,
– some of which ancient Egyptians used
– to construct the Sphinx and the Pyramids of Giza
Coral
• The dominant
reef-building
animals
– of the Cenozoic
Era are corals
– such as this
modern
colonial
Scleractinian
Cenozoic Vegetation and Climate
• During the Cenozoic,
– Angiosperms, or flowering plants,
– continued their diversification
– which had began during the Cretaceous
– as more and more familiar types of plants evolved
• In fact, many Tertiary plants
– would be quite familiar to us today,
– but their geographic distribution was very different
Climatic Change
• Since the Oligocene,
– mean annual temperatures
– have varied somewhat worldwide,
– but overall have not changed much
– in the middle latitudes except
– during the Pleistocene
Herbivores Adapted Quickly
• Many herbivorous mammals
– quickly adapted to these new conditions
– by developing chewing teeth suitable
– for a diet of grass
Other Adaptations
• Penguins adapted to an aquatic environment,
– and in some large extinct and living flightless birds
– the skeleton became robust
– and the wings shrank to vestiges
• One early adaptation involved the evolution
– of large, flightless predatory birds
– such as Diatryma
• This remarkable bird stood more than 2 m tall,
– had a huge head and beak, toes with large claws,
– and small vestigial wings
Archaic Mammals
• These so-called archaic mammals,
–
–
–
–
–
–
such as various marsupials, insectivores,
and the rodent-like multi-tuburculates,
occupied a world
with several new mammalian orders, including
the first rodents, rabbits, primates, and carnivores,
and the ancestors of various hoofed mammals
• But most of these Paleocene mammals,
–
–
–
–
–
even those belonging to orders that still exist,
had not yet become clearly differentiated
from their ancestors,
and the differences between herbivores
and carnivores were slight
Giant Mammals Evolved
• With the evolution of a now extinct order
–
–
–
–
–
known as the Dinocerata,
better known as uintatheres,
and the strange creature known as Arsinoitherium,
giant mammals of one kind or another
have been present ever since
Miocene and Pliocene
• By Miocene and certainly Pliocene time,
– most of the mammals were quite similar to those existing
now
• On close inspection, though,
–
–
–
–
we would see horses with three toes,
cats with huge canine teeth,
Deer-like animals with forked horns on their snouts,
and very tall, slender camels
• We would still see a few odd mammals,
– but overall the fauna would be quite familiar
Insectivora
• Placental mammals of the order Insectivora,
– in a scene from the Late Cretaceous
– None of
these
animals
– measured
more than
a few
centimeters
long
The Meat Eaters—
Carnivorous Mammals
• The order Carnivora is extremely varied,
– consisting of present-day animals as different as
– bears, seals, weasels, skunks, dogs, and cats
• Even though all are predators
– and therefore meat eaters,
– their diets vary considerably
• For example, cats rarely eat anything but meat,
– whereas bears, raccoons, and skunks
– have a varied diet and are thus omnivorous
Cats, Hyenas and Dogs
• Cats, hyenas,
– and viverrids (civits and mongooses)
– share a common ancestry,
– but dogs are rather distantly related
– to the somewhat similar appearing hyenas
• In fact, dogs (family Canidae)
– and hyenas (family Hyenadae)
– not only are similar in appearance
– but also, with few exceptions, are pack hunters
Depend on Speed
• Many hoofed mammals
–
–
–
–
such as antelope and horses
depend on speed
to escape from predators
in their open-grasslands habitat
• As a result they have long slender limbs,
– giving them a greater stride length
• The bones of the palm and sole
– have become very long
Long Slender Limbs
• Long slender limbs in hoofed mammals
– evolved as the bones between the wrist and toes
– and ankle and toes became longer
Grazers Versus Browsers
• Some ungulates,
• horses for example,
–
–
–
–
–
are characterized as grazers
because they eat grass,
as opposed to browsers,
which eat the tender leaves, twigs,
and shoots of trees and shrubs
• Grasses are very abrasive because
– as they grow through soil
– they pick up tiny particles of silt and sand
– that quickly wear teeth down
Camels
• During much of the Cenozoic Era,
– especially in North America,
– camels of one kind or another
– were quite common
• The earliest were small four-toed animals,
– but by Oligocene time all had two toes
• Among the various types
– were very tall giraffe camels,
– slender gazelle-like camels,
– and giants standing 3.5 m high at the shoulder
Adaptations for Grinding
Abrasive Grasses
• Incisor teeth become wider
• Molarization of premolars yields a continuous row of
teeth for grinding vegetation
• Chewing teeth become high-crowned and cement
covered
• Chewing surfaces of premolars and molars become
more complex
• Front of skull and lower jaw become deeper to
accommodate high-crowned teeth
• Face in front of eye becomes longer to accommodate
high-crowned teeth
Pony-Sized Merychippus
• Speed was essential in this habitat,
– and horses’ legs became longer
– and the number of toes was reduced finally to one
• Pony-sized Merychippus is a good example
–
–
–
–
of the early grazing horses;
it still had three toes,
but its teeth were high-crowned
and covered by abrasion-resistant cement
largest land-dwelling
mammal ever
• At more than 5 m high at the shoulder
– and weighing perhaps 13 or 14 metric tons,
– a hornless Oligocene-Miocene rhinoceros
– in Asia was the largest land-dwelling mammal ever
• For the remaining perissodactyls,
– chalicotheres and titanotheres,
– only the titanotheres have a good fossil record
Titanotheres
• Titanotheres existed only during the Eocene,
– giving them the distinction
– of being the shortest lived
– perissodactyl family
• They evolved from small ancestors
– to giants standing 2.5 m high
– at the shoulder
Giant Land-Dwelling
Mammals—Elephants
• A distinctive characteristics of elephants
– is their long snout, or proboscis;
– they are members
– of the order Proboscidea
• During much of the Cenozoic,
–
–
–
–
proboscideans of one kind or another
were widespread on the northern continents,
but now only two species exist,
one in southeast Asia and one in Africa
Transition From Land dweller
• During the transition
– from land-dwelling animals
– to aquatic whales,
– the front limbs modified into paddle-like flippers,
– the rear limbs were lost,
– and the nostrils migrated to the top of the head
• In addition, whales have
– a large, horizontal tail fluke used for propulsion
Years of Little Fossil Evidence
• For many years,
–
–
–
–
paleontologists had little fossil evidence
that bridged the gap
between land-dwelling animals
and fully aquatic whales
• This important transition took place
– in a part of the world where the fossil record was
poorly known
• But beginning 15 or 20 years ago,
– paleontologists have made some remarkable finds
– that resolved this evolutionary enigma
Mammals in Pleistocene
Europe, Asia, and Australia
• Elephants, cave bears, and giant deer
– known as Irish Elk
– lived in Europe and Asia,
• and Australia had 3-m-tall kangaroos
– and wombats the size of rhinoceroses
Pleistocene Fossil Localities
• Paleontologists have
– recovered Pleistocene animals
– from many places in North America,
– but two noteworthy areas are Florida
– and the La Brea Tar pits at Rancho La Brea
– in southern California
• In fact, Florida is one of the few places
– in the eastern United States where fossils
– of Cenozoic land-dwelling animals are common
Mammal Migration in Europe
• For example, reindeer and the Arctic fox
–
–
–
–
lived in southern France
during the last glaciation
and migrated to the Arctic
when the climate became warmer
Arrival of Humans
• Proponents of the prehistoric overkill
hypothesis,
– argue that the mass extinctions
– in North and South America and Australia
– coincided closely with the arrival of humans
• Perhaps hunters had a tremendous impact
– on the faunas of North and South America
– about 11,000 years ago because the animals
– had no previous experience with humans
• The same thing happened
– much earlier in Australia
– soon after people arrived about 40,000 years ago
Scattered Communities
• No large-scale extinctions
– occurred in Africa and most of Europe,
– because animals in those regions
– had long been familiar with humans
• One problem with the prehistoric overkill
hypothesis
–
–
–
–
–
–
is that archaeological evidence indicates
the early human inhabitants
of North and South America,
as well as Australia,
probably lived in small, scattered communities,
gathering food and hunting
Extinctions on Oceanic Islands
• How could a few hunters
– decimate so many species of large mammals?
• However, it is true that, humans
– have caused major extinctions on oceanic islands
• For example, in a period of about 600 years
after arriving in New Zealand,
– humans exterminated several species
– of the large, flightless birds called moas
Multiple Reasons
• The reason for the extinctions
– of large Pleistocene mammals
– is still unresolved
– and probably will be for some time
• It may turn out that the extinctions
– resulted from a combination
– of different circumstances
• Populations that were already
–
–
–
–
under stress from climatic changes
were perhaps more vulnerable to hunting,
especially if smaller females and young animals
were the preferred targets
Land Connection
• During the Early Cenozoic,
–
–
–
–
a land connection existed
between Europe and North America,
allowing mammals to roam
across all the northern continents
• Many did;
– camels and horses are only two examples
Separate Island Continents
• However, the southern continents
– were largely separate island continents
– during much of the Cenozoic
• Africa remained fairly close to Eurasia,
– and, at times, faunal interchange
– between those two continents was possible
• For example, elephants first evolved in Africa,
– but they migrated to all the northern continents
Some Unfamiliar
• However, large horse-like animals with claws
– known as chalicotheres, and some other animals
– would be unfamiliar or at least would be found
– in areas where we would not expect them today
• elephants in the western United States, for instance
Climate and Vegetation Changes
• Rapid changes in climate and vegetation
– occurred over much of Earth's surface
– during the Late Pleistocene,
– as glaciers began retreating
• In the North America and northern Eurasia
– conifer and broadleaf forests replaced
– open-steppe tundras
– as warmer and wetter conditions prevailed
Geologically Short
• Although the Cenozoic
–
–
–
–
constitutes only 1.4% of all geologic time,
this comparatively brief episode
of 66 million years of Earth and life history
was brief only in the context of geologic time
• From the human perspective
– it was far longer than we can even conceive,
– certainly long enough for many changes
– to take place in Earth's biota
Why Didn't
Large Mammals Migrate?
• Rapid changes in climate and vegetation
– can certainly affect animal populations,
– but the climate hypothesis
– presents several problems
• First, why didn't the large mammals
– migrate to more suitable habitats
– as the climate and vegetation changed?
– After all, many other animal species did
Archaic Mammals of the Paleocene
• The archaic mammals of the Paleocene Epoch
included such animals as
Protictus, an early carnivore
Insectivores
the pantodont
Pantolambda,
which stood
about 1 m tall
the
treedwelling
multiturbuculate
Ptolodus
Cenozoic Foraminifera
• Benthonic
foraminifera of the
Cenozoic Era
– Uvigerina cubana
– Late Miocene,
California
Creodont Died Out but Miacids
Evolved Into Existing Carnivores
• 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
Artiodactyls—Even-Toed Hoofed
Mammals
• 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
Pliocene
• Pliocene
mammals
– of western North
American
grasslands
– Amebeledon, a
shovel-tusked
mastodon
– Teleoceras, a
short-legged
rhinoceros
– Cranioceras, a
horned hoofed
mammal
Early Elephant
• One of the earliest members of the order,
–
–
–
–
from the Eocene,
was a 100- to 200-kg creature
called Moeritherium
which possessed few elephant characteristics
• It was probably semiaquatic
Eocene Whales
• Restoration of Protocetus and Basilosaurus
– Although Basilosaurus was a fully aquatic whale
– it differed considerably from today’s whales
Ruminants
• Most living artiodactyls are ruminants,
– which are the cud-chewing animals
– with complex three- or four-chambered stomachs
– in which food is processed to extract more nutrients
• Perissodactyls
– lack such a complex digestive system
Trends in Horses
• Size increase
• Legs and feet become longer: for running
• Lateral toes reduced to vestiges
• Straightening and stiffening of the back
• Adaptations for grinding abrasive grasses
• Larger, more complex brain