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

• 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

73
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

74
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

75
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

76
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

77
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

78
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

79
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

80
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

81
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

82
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

83
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

84
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

85
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

86
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

87
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

88
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

89
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

90
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

91
Summary

• Changes in climate and prehistoric overkill
• are the two hypotheses
• explaining Pleistocene extinctions

92
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

93
John Day Fossil Restoration

• The dryer conditions that prevailed
• when the John Day Formation was deposited

94
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

95
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

96
Recently Birds Diversity Decreased

• Birds adapted to numerous habitats
• and continued to diversify into the Pleistocene,
• but since then their diversity
• has decreased slightly

97
Mammals
98
Mammals
99
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

100
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

101
Powerful Hind Limbs

• The development of long, powerful hind limbs
• for hopping and speed
• is the most obvious evolutionary trend
• in rabbits

102
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

103
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

104
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

105
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

106
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

107
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

108
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

109
Pliocene and Pleistocene Mammals of Florida

• 6-m-long giant sloths
• armored animals known as glyptodonts

110
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

111
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 jawskull
  joints
• and the distinction
• between cynodonts and the earliest mammals
• is difficult to make

112
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

113
Cenozoic Foraminifera

• Benthonic foraminifera of the Cenozoic Era

• Lenticulina mexicana
• Eocene, Louisiana

114
Cenozoic Foraminifera

• A planktonic form

• Globigerinoides fistulosus
• Pleistocene,
• South Pacific Ocean

115
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

116
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

117
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 biscuit-shaped ancestors

118
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

119
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

120
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

121
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

122
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

123
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

124
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

125
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

126
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

127
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

128
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

129
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

130
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

131
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

132
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

133
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

134
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

135
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

136
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

137
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

138
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

139
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

140
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

141
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

142
Bat Wings

• Unlike pterosaurs and birds,
• bats use a modification of the hand
• in which four long fingers
• support their wings

143
Jaws of Large Cats

• This present-day skull and jaw of a large cat
• show the specialized sharp-crested shearing teeth
  
• of c