CHAPTER 16—LIFE OF THE CENOZOIC
CHAPTER OVERVIEW
The Cenozoic has been called the “Age of Mammals.” During the Cenozoic mammals expanded rapidly
into several habitats given the diversity of angiosperms and grasses. Numerous evolutionary advances of
herbivorous mammals can be correlated with the development of extensive grasslands of the Miocene as
well as carnivorous mammalian predators. (Table 16-1, Page 501) Among marine invertebrates, large
discoidal foraminifera known as nummulites and smaller plankton forms proliferated and underwent a
marked diversification during the Cenozoic as did gastropods and pelecypods. Reef corals grew
extensively across tracts of shallow warm marine environments.
This chapter also examines the evolutionary history of the horse in response to changes within the
environment as well as the phylogenetic history of monotremes, marsupials, and placental mammals.
Taxonomic principles on how to distinguish between the principle subclasses of mammals are discussed.
A general description of features is given for the following: Credonta, Carnivora, Artiodactyla, Cetacea,
Tethytheria,, and Perissodactyla. This chapter concludes with an examination of several view points on
the extinction of many Pleistocene mammals.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:









Discuss the development of angiosperms and grasses within the Miocene and the influence
on the proliferation of foraging and grazing mammals.
Explain the significance of foraminifera, the variation these forms underwent in response to
changes in the climate and their use in correlation.
Discuss the evolution of teleost fish, including the effect of the enormous range of adaptive
radiation on this process.
Discuss the evolutionary changes that reptiles and birds underwent within the Cenozoic
including extinctions.
Describe the differences between Perissodactyls and Artiodactyls including the major hoofed
groups classified under each.
Explain the evolutionary history of the horse and the changes it underwent during the
Cenozoic including the number of toes, dentition, skull size, and height.
Describe how monotremes, marsupials, and placental mammals differed within the Cenozoic
and identify which were successful.
Explain how continental fragmentation stimulated biological diversity and resulted in distinctive
faunal radiation on separated land masses.
Discuss the different view points that are presented regarding the extinction of mammals at
the end of the Cenozoic including Pleistocene Glaciation, the North American-South American
Land Bridge, and human predation.
CHAPTER OUTLINE
I.
Grasslands Expand, Mammals Respond
II.
Plankton
III.
Marine Invertebrates
A. Corals and South Pacific Atolls
B. Mollusks
C. Echinoderms, Bryozoans, Brachiopods, and Arthropoda
IV.
Vertebrates
A. Fishes
B. Amphibians
Chapter 16—Life of the Cenozoic
C. Reptiles
D. Birds
V.
Mammals
A. Characteristics of Mammals
B. Earliest Mammals
C. Mammal Groups and Their Features
VI.
Monotremes
VII.
Marsupials
VIII.
Placental Mammals
A. Insectivores
B. Edentates
C. Rodents
D. Rabbits
E. Bats
F. Flesh-Eaters
G. Ungulates – Hoofed Animals
1. Perissodactyls (“Uneven Toes” – One or Three)
2. Horse Family Tree
3. Artiodactyls (“Even Toes” – Two or Four)
4. Ruminants
H. Elephants and Kin
1. Mammoths (Ice Age Elephants)
2. Cetaceans (Whales and Porpoises)
IX.
Demise of the Pleistocene Giants
1. Human Predation
2. Climate Change
Chapter 16—Life of the Cenozoic
KEY TERMS
(Pages 487–523)
arsinothere (509): Huge mammals belonging to the group called ungulates (animals with hoofs) that
sported an enormous pair of side-by-side horns over their skull and snout.
artiodactyl (512): Hoofed mammals that typically have two or four toes on each foot.
atoll (493): A ringlike island or a series of islands formed by corals and calcareous algae around a central
lagoon.
barrier reef (493): A long, narrow coral reef roughly parallel to the shore. If the coral growth is able to
keep pace with the subsidence they will continue to grow.
bovid (516): A group that includes cattle, sheep, goats, muskoxen, and antelopes, are presently the most
numerous of ruminants.
brontothere (511): A group of large perissodactyls with huge, blunt-forked horns over their snouts that
were used for sexual display and jousting with other males to gain access to receptive females.
carnassials teeth (506): Cheek teeth that were developed into blades able to shear past one another and
slice meat into small pieces.
Carnivora (507): Flesh-eating placental mammals, having a common ancestry with the creodonts. The
expansion of the carnivores during the late Tertiary, producing a host of familiar flesh-eaters, including
bears, raccoons, weasels, genets, hyenas, dogs, and cats.
castormorph (506): Term includes beavers and their relatives. A Pleistocene member called Paleocastor
left casts of peculiar corkscrew burrows.
cetacean (519): Whales and porpoises. Whales are descendants of carnivorous land animals, and the
earliest whales known had legs and could both swim and walk.
chalicothere (511): Extinct perissodactyls having robust claws rather than hoofs.
convergent evolution (504): The process by which similarity of form or structure arises among different
organisms as a result of their becoming adapted to similar habitats.
Creodonta (506): Primitive, early, flesh-eating placental mammals.
dinothere (517): A division of the proboscideans that included Miocene and Pliocene animals with
distinctive tusks that were present only in the lower jaws and curved downward and backward, an
orientation presumably useful for uprooting plants and digging for roots and tubers.
edentates (505): Descendants of insectovores. Armadillos, tree sloths, and South American anteaters
are endentates that have not become extinct.
entelodont (512): Repulsive-looking, hog-like beasts. Their trademarks were curious bony processes
that grew along the sides of the skull and jaws.
fringing reef (493): A reef built by corals around the perimeters of volcanic islands that had been
erosionally truncated during a glacial period of low sea level.
glyptodonts (505): Extinct edentates that survived in South America until about 7,000 years ago.
Glyptodonts were about the size of a Volkswagen “Beetle” with a spike-covered knob on its tail for
bludgeoning predators.
Chapter 16—Life of the Cenozoic
mammoth (517): The name commonly applied to extinct elephants of the Pleistocene Epoch.
marsupial (503): Mammals of the order Marsupialia. Female marsupials bear mammary glands and
carry their immature young in a stomach pouch.
mastodon (516): One of a group of extinct, elephant mammals widely distributed in the Northern
Hemisphere during the Oligocene and Pleistocene.
monotreme (502): The egg-laying mammals.
myomorph (506): Rodents that evolved during the late Paleogene and would include hamsters, rats, and
mice.
oreodont (512): North American artiodactyls of the middle and late Tertiary. Short, stocky grazers that
roamed the grassy plains of North America in enormous numbers.
placental mammal (505): The tiny tree shrew living today is anatomically very close to the ancestor of
Cenozoic primates, rodents, bates, carnivores, and herbivores.
perissodactyl (509): Progressive, hoofed mammals, characteristically having an odd number of toes on
the hind feet and usually on the front feet as well.
proboscidean (509): Animals that have a trunk, such as elephants and their progenitors.
protorogomorphs (506): A division of the Rodentia which originated in the Paleocene. Protorgomorphs
were ancestors of the later true squirrels and old world porcupines.
ruminant (515): A herbivorous, cud-chewing ungulate. The most varied and abundant of modern-day
artiodactyls.
sciuromorph (506): A division of the Rodentia in which squirrels are the characteristic rodent. This group
includes chipmunks and marmots.
scleractinid (492): Modern reef corals belong to an order of the phylum Cnidaria named Scleractinia.
They would later evolve to form the major reef-builders of the Cenozoic.
squamate (498): The order of reptiles that both snakes and lizards belong to; by far the most varied and
numerous of living reptiles.
teleost (496): The most advanced of the bony fishes, characterized by thin, rounded scales, completely
bony internal skeleton, and symmetric tail. Teleosts range from Cretaceous to Recent.
ungulate (509): Four-legged mammals whose toes bear hoofs. They are the largest category of
Cenozoic plant-eaters.
Chapter 16—Life of the Cenozoic
MULTIPLE-CHOICE QUESTIONS
1.
The Cretaceous saw the development and expansion of what type of plant?
a. angiosperms
c. psilophytes
b. gymnosperms
d. chlorophytes
2.
The globigerinids and nummulitids belong to what order of marine organisms?
a. radiolaria
c. foraminifera
b. diatom
d. teleosts
3.
The pyramids and other structures in ancient Egypt were constructed from marine limestones
containing
a. diatoms.
c. foraminifers.
b. radiolaria.
d. acritarchs.
4.
All living orders of mammals had evolved by the
a. Paleocene.
c. Miocene.
b. Eocene.
d. Oligocene.
5.
Open prairie and grassland habitats coincide with the appearance of what type of mammals in the
fossil record?
a. carnivores
c. scavengers
b. herbivores
d. omnivores
6.
How many cervical (neck) vertebrae are typically found in modern mammals?
a. five
c. nine
b. seven
d. ten
7.
Teleosts are
a. amphibians.
b. reptiles.
c. bony fishes.
d. mollusks.
8.
One of the characteristics of Cenozoic avian fauna is the presence on all continents of
a. large, flightless, terrestrial, flesh-eating birds.
b. songbirds.
c. flightless, aquatic birds.
d. forest-dwelling birds.
9.
During the Cenozoic, marsupial mammals were found only in
a. Australia and Africa.
c. Australia and South America.
b. Australia and India.
d. Australia and North America
10.
The most primitive of all living mammals lays eggs like a reptile and are called
a. monotremes.
c. edentates.
b. marsupials.
d. creodonts.
11.
The name of the group of even-toed, hoofed mammals is the
a. perissodactyls.
c. edentates.
b. monotremes.
d. artiodactyls.
12.
The family tree of horses presently appears to have its roots in a small herbivore from the
Paleocene of China named
a. radinskya.
c. merychippus.
b. protapirus.
d. equus.
Chapter 16—Life of the Cenozoic
13.
Which of the following is not a trend in the evolution of the horse?
a. increase in size
c. reduction of lateral (side) toes
b. decrease in length of legs
d. increase in the complexity of the teeth
14.
The tusks of elephants are
a. modified canine teeth.
b. modified incisor teeth.
c. modified molars.
d. enlarged nasal bones.
15.
Edentate mammals (toothless) having no teeth at all, or very few would include only
a. wombats.
d. armadillos.
b. koalas.
e. bandicoots.
c. phalangers.
16.
Monotreme mammals would include only which one of the following?
a. wombat
d. kangaroo
b. platypus
e. armadillo
c. opossum
17.
The reptile group that includes lizards and snakes and are by far the most varied and numerous of
living reptiles is called
a. teleosts.
d. ocaecilians.
b. gavials.
e. tuatara.
c. squamates.
18.
The benthonic paleotathymetric indicators that live in particular depths of water and are excellent
indicators of ancient water depths are called
a. scleractinids.
d. coccoliths.
b. rudistids.
e. foraminifers.
c. dinoflagellatges.
19.
Cenozoic mollusk shells that look very much like those found along coastlines today would include
all but
a. ammonites.
d. scallops.
b. clams.
e. oysters.
c. mussels.
20.
Perissodactyls (uneven toed) mammals would include all but
a. rhinoceroses.
d. brontotheres.
b. modern horses.
e. giraffe.
c. tapirs.
Chapter 16—Life of the Cenozoic
FILL IN THE BLANK
1.
Ringlike coral reefs that grow around a central lagoon are called
.
2.
Used for correlating strata the members of Sarcodina that occurred in incredible numbers and
variety were called
.
3.
The primitive inarticulate brachiopod that has an exceptionally long, fleshy, muscular pedicle and
gets its name from its tongue shape is called
.
4.
Bony fish that evolved to the highest level of ossification and skeletal perfection are called
.
5.
Both lizards and snakes belong to an order of reptiles called
6.
The most primitive of all living mammals that still lays eggs in a reptilian manner is
.
.
7. Cetaceans who are characterized with having blubber for insulation, tail and fore-limbs modified for
swimming would include ____________ and ____________.
8. The type of evolution illustrated by the similarity between the South American marsupial
Thylacosmilus and the North American sabertooth Smilodon is called
evolution
9.
Armadillos, tree sloths, and South American anteaters are examples of what order of mammals?
.
10.
By the end of the Cretaceous and continuing into the Paleocene, flesh-eating mammals had been
split into two independent orders: carnivores with evolved larger brains and a second group that
possessed relatively smaller-brained animals with shorter limbs, clawed toes, and long nails called
.
11.
Among mammals, more have adapted to life in the seas as the cetaceans (whales and porpoises)
that are descendants from predatory, hoof-bearing land dwellers known as
12.
Within Tethytheria, ungulates is the order designation that includes elephants, mammoths, and
mastodonts. They are called
.
13.
________________ are mammals that nurture their young in an external pouch.
14.
Two groups of periossodactyls known only from fossils are the _________________ and
_________________.
15.
Camels, pigs, ruminants, hippopotami, and whales have a close evolutionary relationship to
___________________.
.
Chapter 16—Life of the Cenozoic
TRUE-FALSE
1.
Flowering plants continued to expand and diversify, with the most important single
occurrence being the Miocene proliferation of grasses as extensive prairies.
2.
Cenozoic marine mammals, such as whales and porpoises, belong to the group called
Creodonta.
3.
A general name for herbivorous, cud-chewing ungulates is ruminants.
4.
The evolution of the camel occurred primarily in North America.
5.
The development of atolls is related to either subsidence of an island or a rise in sea
level.
6.
Corals require shallow, warm water with large amounts of terrigenous sediment and low
sunlight for photosynthesis.
7.
Although the rudistid pelecypods and ammonoid cephalopods had been thriving groups
during the Mesozoic, they did not survive into the Cenozoic.
8.
The tusks of mastodonts and elephants are elongation of the second pair of incisors.
9.
Marsupials were common both in Australia and Africa during the Cenozoic.
10.
One of the more apparent trends in the evolution of elephants was a multiplication in the
number of cross crests on the incisors.
Chapter 16—Life of the Cenozoic
ANSWER KEY
Multiple Choice
1. a
2. c
3. c
4. d
5. b
6. b
7. c
8. a
9. c
10. a
11. d
12. a
13. b
14. b
15. d
16. b
17. c
18. e
19. a
20. e
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
atolls
Foraminifera
lingula
teleosts
squamata
monotremes
whales, dolphins
convergent
edentates
credenta
Pakicetus
proboscidians
marsupials
brontotheres,
chalicotheres
15. Artiodactyls
True/False
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
T
F
T
T
T
F
T
T
F
F
Chapter 16—Life of the Cenozoic
RESPONSES TO QUESTIONS ACCOMPANYING
SELECTED FIGURES
FIGURE 16–3 (p. 490) Frustules of diatoms are composed of silica.
FIGURE 16–22 (p. 502) Although they reproduce by laying eggs, monotremes have a body
covering of hair. Also, the young are suckled with milk. In addition, monotremes possess the
mammalian number of seven cervical vertebrae and have mammalian features of the lower jaw
and ear.
FIGURE 16–45 (p. 514) The sequence of figures depicts landscapes that reflect the gradually
cooling climates of the Cenozoic.