R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
CHAPTER 18
LIFE OF THE CENOZOIC ERA
OUTLINE
INTRODUCTION
MARINE INVERTEBRATES AND PHYTOPLANKTON
PERSPECTIVE The Messel Pit Fossil Site in Germany
CENOZOIC VEGETATION AND CLIMATE
CENOZOIC BIRDS
THE AGE OF MAMMALS BEGINS
Monotremes and Marsupial Mammals
Diversification of Placental Mammals
PALEOGENE AND NEOGENE MAMMALS
Small Mammals—Insectivores, Rodents, Rabbits, and Bats
A Brief History of the Primates
The Meat Eaters – Carnivorous Mammals
The Ungulates or Hoofed Mammals
Giant Land-Dwelling Mammals—Elephants
Giant Aquatic Mammals—Whales
PLEISTOCENE FAUNAS
Ice Age Mammals
Pleistocene Extinctions
INTERCONTINENTAL MIGRATIONS
SUMMARY
CHAPTER OBJECTIVES
The following content objectives are presented in Chapter 18:
 Survivors of the Mesozoic extinctions evolved and gave rise to the present-day
invertebrate marine fauna.
 Angiosperms continued to diversify and to dominate land plant communities, but
seedless vascular plants and gymnosperms are still common.
 Many of today’s families and genera of birds evolved, and large flightless birds were
important Early Cenozoic predators.
 If we could visit the Paleocene, we would not recognize many of the mammals, but
more familiar ones evolved during the following epochs.
 Small mammals such as rodents, rabbits, insectivores, and bats adapted to the
microhabitats unavailable to large mammals.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
 Carnivorous mammal fossils are not as common as those of herbivores, but there are
enough to show their evolutionary trends and relationships to one another.
 The evolutionary histories of odd-toed and even-toed hoofed mammals are well
documented by fossils.
 Today’s giant land mammals (elephants) and giant marine mammals (whales)
evolved from small Early Cenozoic ancestors.
 Extinctions at the end of the Pleistocene Epoch were most severe in the Americas and
Australia, and the animals most affected were large land-dwelling mammals.
 As Pangaea continued to fragment during the Cenozoic, intercontinental migrations
became increasingly difficult.
 A Late Cenozoic land connection formed between North and South America,
resulting in migrations in both directions.
LEARNING OBJECTIVES
To exhibit mastery of this chapter, students should be able to demonstrate comprehension
of the following:
 the composition of Cenozoic marine invertebrate communities
 the distribution of Paleogene and Neogene vegetation and its climatic significance
 the continuing evolution of birds
 the diversification of mammals, especially placental mammals
 the nature of archaic Paleocene-Eocene mammalian faunas compared to those of the
later Cenozoic
 adaptive radiation and evolutionary trends in hoofed animals
 the significance of gigantism in Pleistocene mammals
 the distribution of mammals as related to plate tectonics
 the hypotheses for the Pleistocene extinction event
CHAPTER SUMMARY
1. The marine invertebrate groups that survived the Mesozoic extinctions diversified
throughout the Cenozoic. Bivalves, gastropods, corals, and several kinds of
phytoplankton such as foraminifera proliferated.
Figure 18.1 Restoration of Fossils from the Eocene-aged Clarno Formation in
John Day Fossil Beds National Monument, Oregon
Figure 18.2 Miocene Diatomite and Diatoms
Figure 18.3 Cenozoic Foraminifera
Figure 18.4 Cenozoic Fossil Invertebrates
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
2. During much of the Early Cenozoic, North America was covered by subtropical
and tropical forests, but the climate became drier by Oligocene and Miocene time,
especially in the midcontinent region.
Figure 18.5 Cenozoic Vegetation and Climate
3. Birds belonging to living orders and families evolved during the Paleogene Period.
Large, flightless predatory birds of the Paleogene were eventually replaced by
mammalian predators.
Figure 18.6 Restoration of Diatryma
Enrichment Topic 1. Shorebird Population in Rapid Decline.
Since records have been kept of bird populations, 20% of species have gone extinct. In
March 2008, a 24-year survey reported the decline in Australian and Asian shorebirds,
beginning in the mid-1980s. Migratory shorebirds of Australia dropped to 73%, while
resident Australian shorebirds had been reduced to 81%. Wetland loss from damming and
river diversion is partly responsible for decline. Wright, “Shorebird Population in Rapid
Decline,” Discover, January 2009, p. 42-43.
4. Evolutionary history is better known for mammals than for other classes of
vertebrates, because mammals have a good fossil record and their teeth are so
distinctive.
Enrichment Topic 2. Vertebrates and Tectonics
Paleobiologist Malcolm McKenna proposed a proto-Iceland that once connected North
America to Europe, 56 million years ago. While most researchers acknowledge a land
bridge between Siberia and Alaska, McKenna proposed that 55 million years ago, it was
possible to “walk from New Mexico to Paris, without changing latitude.” This land
bridge may have allowed species to migrate between continents, but researchers pointed
out that the land bridge would also have blocked circulation between the Arctic and
Atlantic oceans. Furthermore, changes in ocean temperature would have occurred when
the land bridge broke, which may have led to intense global warming in the PaleoceneEocene boundary. The hypothesis also explains an extinction of benthonic foraminifera.
Other geologists question the new hypothesis, however. “Vertebrates and Tectonics,”
Geotimes, December 2003, v.48 n.12 p.8-9.
5. Egg-laying mammals (monotremes) and marsupials exist mostly in the Australian
region. The placental mammals—by far the most common mammals—owe their
success to their method of reproduction. All placental and marsupial mammals
descended from shrew-like ancestors that existed from Late Cretaceous to
Paleogene time.
Figure 18.7 Mammals Existed During the Mesozoic, but Most Placental
Mammals Diversified During the Paleocene and Eocene Epochs
Figure 18.8 Archaic Mammals of the Paleocene Epoch
Figure 18.9 Some of the Earliest Large Mammals
Figure 18.10 Pliocene Mammals of the Western North American Grasslands
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
6. Small mammals such as insectivores, rodents, and rabbits occupy the microhabitats
unavailable to larger animals. Bats, the only flying mammals, have forelimbs
modified into wings but otherwise differ little from their ancestors.
Figure 18.11 Fossil Rodents
Enrichment Topic 3. Move Over, Ratzilla.
A rat skull dating 4 million years old was found in 2008 in Uruguay. This skull belonged
to a creature as large as a bull, and as heavy as a small car. The new “champion” rat,
Josephoartigasia monesi, lived in forests near river deltas or estuaries. This large
vegetarian probably survived until 3 million years ago, when the intercontinental
migration brought North American bears and cats into its range. (Dickinson, “Ancient
Rat as Big as a Bull,” Discover, January 2009, p. 79.
7. Most carnivorous mammals have well-developed canines and specialized shearing
teeth, although some aquatic carnivores such as seals have peglike teeth.
Figure 18.12 Teeth of Carnivorous Mammals
Figure 18.13 Today’s Carnivorous Mammals Evolved from a Primitive Group
Known as Miacids
Enrichment Topic 4. Venomous Mammals?
Richard Fox, paleontologist, found some fossils of a 60 million-year-old mammals. The
fragments featured a long, pointed canine tooth that resembled venom-delivery structures.
In fact, the groove in the canine tooth parallels channels found in some venomous snakes.
Few modern mammals are known for venoms: Only the two species of solenodons living
in Haiti and Cuba have grooves in their teeth for venom delivery. Mark Dufton,
biochemist, suggested that early mammals may have been limited by their size, and oral
venom would have been an asset. “Killer Bite,” Science News, June 25, 2005, v.164 n.20
p.403.
8. The most common ungulates are the even-toed hoofed mammals (artiodactyls) and
odd-toed hoofed mammals (perissodactyls), both of which evolved during the
Eocene. Many ungulates show evolutionary trends such as molarization of the
premolars as well as lengthening of the legs for speed.
Figure 18.14 Characteristics and Evolutionary Trends in Hoofed Mammals
9. During the Paleogene, perissodactyls were more common than artiodactyls but now
their 16 living species constitute less than 10% of the world’s hoofed mammal
fauna.
Figure 18.15 Relationships among the Artiodactyls (Even-Toed Hoofed
Mammals)
10. 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.
Figure 18.16 Evolution of Horses
Table 18.1 Trends in the Cenozoic Evolution of the Present-Day Horse Equus
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
11. Even though horses, rhinoceroses, tapirs, as well as the extinct titanotheres and
chalicotheres, do not closely resemble one another, fossils show they diverged from
a common ancestor during the Eocene.
12. During much of the Cenozoic Era, proboscideans of one kind or another were
widespread on northern continents, but now only three species exist.
Figure 18.17 Phylogeny of Elephants and Some of Their Relatives
13. The fossil record for whales is now complete enough to verify that they evolved
from land-dwelling ancestors.
Figure 18.18 Relationships among Whales and Their Land-Dwelling Ancestors
Enrichment Topic 5. From Where the Whale?
Paleontologists look at the skeletal morphology of modern organisms and ancient fossils
to find similarities and differences. Molecular biologists look at genes to see how many
the modern and fossil organism had in common. Until recently these two groups had very
different answers for the ancestor of whales. They did agree that cetaceans evolved from
four-legged animals that roamed the land, with nostrils near the tips of their noses and
teeth of several sizes and types. Cetaceans moved into the sea during the Eocene, almost
50 million years ago. Scientists, however, disagreed on other issues. The paleontologists
thought that ancient whales were members of an extinct group of highly-specialized
ungulates (hoofed mammals) called mesonychians. Molecular biologists favored
artiodactyls (even-toed ungulates such as cows, pigs, camels, deer, and hippos) as the
ancestors of cetaceans. Recently discovered complete cetacean fossils, 49 million years
old, have brought paleontologists over to the side of the molecular biologists. This peacemaking fossil was wolf-sized Pakicetus attocki, a meat eater, similar to modern dogs but
with more a powerful tail, longer snout and smaller eyes. Pakicetus was a landlubber;
adapted to walking and running on land, but also may have fed while wading in streams.
Pakicetids are thought to be ancestral to cetaceans because of the structure of their ear
bones and anklebones. “From Where the Whale?” Oct. 2001,
www.studyworksonline.com.
Enrichment Topic 6. Blue Whale Ancestor
A ferocious fossil whale with sharp, 3 cm long teeth has been found in Australia. The 25
million year fossils are from an early type of baleen whale, although the new fossil
discovery did not have baleen. Instead, the whale was a powerful predator that captured
its prey, perhaps sharks. The recent discovery has caused the rewriting of baleen whale
evolution. In addition to sharp teeth, the whale also had large eyes, suitable for hunting.
“Report: Blue Whale Ancestor Was No Gentle Giant,” Reuters, August 2006,
http://www.cnn.com/2006/TECH/science/08/16/blue.whale.ancestor.reut/index.html
14. One important evolutionary trend in Pleistocene mammals and some birds was
toward gigantism. Many of these large species died out, beginning about 40,000
years ago. Pleistocene mammalian fauna is remarkable in that so many large species
existed.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
Horses, camels, elephants, and other mammals spread across the northern
continents during the Cenozoic because land connections existed between those
landmasses at various times
Figure 18.19 The Irish Elk
Figure 18.20 Pleistocene Fossils from Florida and California
15. Changes in climate and prehistoric overkill are the two hypotheses explaining
Pleistocene extinctions.
Enrichment Topic 7. Were Humans Responsible for Mammoth Extinction?
Dale Guthrie reported in 2006 that climate shifts were probably responsible for the
mammoth extinctions, and not over-hunting by humans. He used radiocarbon dating of
bones from bison, moose, and humans that survived the extinction, and bones of
mammoth and wild horses that did not survive. Guthrie stated that radiocarbon dates
showed that numbers of bison were actually expanding—before and during human
colonization. He concluded that climate shifts were responsible, because they resulted in
vegetation changes to which the wild horses and mammoths could not adapt. “Scientist:
Humans Not Responsible for Mammoth Extinction,” Reuters, May 13, 2006,
http://www.cnn.com/2006/TECH/science/05/10/mammoth.extinction.reut/index.html
16. During most of the Cenozoic, South America was isolated, and its mammal fauna
was unique. A land connection was established between the Americas during the
Late Cenozoic, and migrations in both directions took place.
Figure 18.21 The Great American Interchange
Enrichment Topic 8. Did Blond Mammoths Have More Fun?
An analysis of 43,000-year-old DNA from prehistoric mammoths indicated that some of
them possessed blond fur, a finding that supported previous visual analyses of mammoth
hair, which appears to come in a variety of colors. When investigating the DNA,
researchers found a key pigmentation gene, Mc1r, which exists in two varieties. When
researchers investigated further, they determined that one of the gene versions functioned
better than the other for production of brown pigment. The researchers proposed that the
weaker gene version produced lighter brown, blonde, or red shades. “Mammoths Get
Lighter: DNA Analysis Says There Were Probably Woolly Blondes,”
News@Nature.com, July 10, 2006, http://www.nature.com//news/2006/060703-14.html
LECTURE SUGGESTIONS
Life after the Extinction
1. Discuss how Earth may have appeared when the Cenozoic Era began: Which
organisms survived the Mesozoic mass extinction, and which organisms did not?
Discuss how the majority of the top terrestrial and marine organisms—in the form
of reptiles—were now extinct.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
2. Why were mammals better equipped to radiate and diversify following the
extinction?
3. Did the flying organisms encounter similar extinctions at the end of the
Mesozoic? Which flying organisms dominated in the Mesozoic, and which
dominate in modern times?
4. Discuss how the marine invertebrate communities changed following the
Mesozoic extinction, and compare these changes to those that followed the
Paleozoic extinction. In which extinction did marine invertebrates face the greater
losses?
Evolution of the Horse
The evolution of the horse is a great example to review evolution by gradualistic changes.
There are several fossil intermediates of the horse. Discuss the evolutionary trends
surrounding body size, teeth, elongation of the skull, length of limbs, and number of
digits. Why might each of these changes have given the horse an advantage via natural
selection?
Cope’s Rule
1. Cope’s Rule states that organisms tend to increase in body size over evolutionary
time. Have the class investigate when mammals were at their largest sizes. When
did some of these larger mammals become extinct? What were the possible
reasons for the extinction events?
2. On islands, organisms tend to stay small because of limited natural resources and
the competition for these resources. Are there modern examples of smaller life
forms on islands that the students can uncover?
CONSIDER THIS
1. Is the term “Age of Mammals" a fair assessment of the Cenozoic Era? Is there a
better term that should be used?
2. Why do you think the top marine predators of the Mesozoic were reptiles, but
they relinquished that role in the Cenozoic?
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
IMPORTANT TERMS
Artiodactyla
browser
carnassials
Carnivora
Cetacea
grazer
Hyracotherium
molar
molarization
Paleocene-Eocene Thermal
Maximum
Perissodactyla
premolar
Primates
Proboscidea
ruminant
ungulate
SUGGESTED MEDIA
Videos
1. Walking with Prehistoric Beasts, BBC
2. Prehistoric America, BBC
3. Life of Birds by David Attenborough, BBC
4. Life of Mammals, BBC
5. Miracle Planet, Survival of the Fittest, The Science Channel
6. PaleoWorld, Are Rhinos Dinos?, The Learning Channel
7. PaleoWorld, Attack of the Killer Kangaroos, The Learning Channel
8. PaleoWorld, Back to the Seas, The Learning Channel
9. PaleoWorld, Dawn of the Cats, The Learning Channel
10. PaleoWorld, Island of the Giant Rats, The Learning Channel
11. PaleoWorld, Killer Birds, The Learning Channel
12. Life on Earth, The Hunters and the Hunted, BBC
13. Nature: Triumph of Life: The Survivors, PBS Home Video
14. Mammoths of the Ice Age, WGBH Boston
15. Lost Worlds, Vanished Lives, The Rare Glimpses, BBC
16. Life in the Cenozoic, Physical Geography II
Demonstration Aids and Slides
1. Evolution of Life on Earth, slide set, Educational Images, Ltd.
2. Cenozoic Fossil Collection, Science Stuff
CHAPTER 18 – ANSWERS TO QUESTIONS IN TEXT
Multiple Choice Review Questions
1.
2.
3.
4.
b
a
c
d
5.
6.
7.
8.
b
e
b
c
9. a
10. b
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
Short Answer Essay Review Questions
11. South America was isolated from all other landmasses from Late Cretaceous until a
land connection with North America formed about 5 million years ago. Before the
connection, South American fauna was made up of marsupials and several orders
of placental mammals that lived nowhere else. However, when the Isthmus of
Panama formed, migrations took place in both directions. As a result of the great
American interchange, about 50% of South American’s modern mammals came
from the north.
12. As they became grazers, the animals’ teeth became high-crowned and abrasionresistant for chewing grasses. They evolved long, slender limbs as the bones
between the wrist and toes and ankles and toes became longer. Their long limbs
allowed them to see over grasses and to run fast with greater stride length. Their
toes became weight-bearing.
13.
Western North America has rocks of the right ages for fossil mammals but eastern
rocks are predominantly older.
14.
Large leaves with smooth, entire margins characterize rainy, warm climates, while
small leaves with incised margins typify cooler, drier regions
15.
In the early Cenozoic, one of the early adaptations in birds was the evolution of
large, flightless predators such as Diatryma, which stood more than 2 meters tall.
These early predators were widespread in North America and Europe during the
Paleogene, and in South America they were the dominant predators until about 25
million years ago. Eventually they died out and were replaced by carnivorous
mammals.
16. The three trends in whale evolution are (a) increase in body size, (b) modification
of the front limbs to paddlelike flippers, and loss of the rear limbs (vestigial organs
indicate their former presence and function), and (c) migration of the nostrils to the
top of the head.
17. There are four evolutionary trends in horses: (a) a decrease in the number of toes,
(b) an increase in size, (c) lengthening of the limbs, and (d) the development of
high-crowned teeth with complex chewing surfaces.
18. The Paleocene fossil ferns and palms in the western interior of North America
indicate a warm, subtropical climate. About 55 million years ago a large scale
oceanic circulation was disrupted, and an abrupt warming trend took place, known
as the Paleocene-Eocene Thermal Maximum. Subtropical conditions persisted in
the Eocene, probably the warmest of all Cenozoic epochs. A major climate change
took place at the end of the Eocene, when mean annual temperatures dropped as
much as 7oC in 3 million years. A general decrease in precipitation during the last
25 million years took place in the mid-continent of North American, and the vast
forests of the Oligocene gave way to savannah conditions, then steppe conditions.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
Our Pleistocene Ice Age ended about 10,000 years ago, and temperatures have risen
since then.
19. The Paleocene fauna are considered archaic because, although several orders of
mammals were present, some were simply holdovers from the Mesozoic or
belonged to new, but short-lived groups that have no living descendants.
20. Although dogs and hyenas are similar in appearance and are pack hunters, they are
only distantly related. Hyenas are more closely related to cats and mongooses and
their similarity to dogs is because of convergent evolution.
Apply Your Knowledge
1. One anomalous feature of this assemblage of fossils is the number of carnivores.
With endothermic animals, the ratio of predator to prey is a low number (usually
less than 5%), because endothermic animals have a large energy requirement.
“Several” horses, camels, and mastodons would not be enough animals to sustain
“dozens” of saber-toothed cats, dogs, and vultures (all predators). The organic
mudstones and claystones indicate a shallow environment, perhaps a swampy
area. If large animals came to this paleoenvironment to drink, they might have
become mired or trapped in the area. Trapped animals and decaying carcasses
would attract predators to the site, and these animals likely became trapped as
well. The large occurrence of fossil carnivores is also noted at La Brea Tar Pits in
Los Angeles, California, where a similar scenario likely played out in the
Pleistocene.
2. Carnivorous mammals can be identified by their specialized shearing teeth, or
carnassials, and sharp pointed canine teeth. In herbivorous mammals, the canines
are not well developed, but instead the teeth show molarization to provide a
continuous row of grinding teeth. Grazers, or animals that eat grass, evolved highcrowned cement-covered chewing teeth. Browsers, or animals that ate bushes and
shrubs, have molars, but do not have the high-crowned teeth found in grazers.
Speedy runners can be detected by the long, slender limb bones. As hoofed
mammals evolved for speed, the bones between the wrist and toes and the ankle
and toes became longer. In contrast, mammals such as rhinoceroses have sturdy
limb bones to support their large weight. Plant fossils can be used to indicate
ancient climates. The smaller leaves with incised margins are more indicative of
cooler, drier areas, while leaves with entire or smooth margins and drip-tips
dominate in areas with abundant rainfall and high annual temperatures.
3. Student answers will vary greatly. Example: The first vertebrates to evolve were
fish. Eventually, fish with articulating bones in their fins evolved to survive in
swampy environments. From these fish, limbs evolved via natural selection, and
amphibians eventually moved onto the land. However, these amphibians, just like
the frogs we have today, had to return to the water to lay their eggs.
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R.M. Clary, Ph.D., F.G.S.
Department of Geosciences
Mississippi State University
When reptiles evolved from amphibians, they had tough skin and were able to
reproduce with shelled eggs. They did not need to return to the water to
reproduce. From early reptiles, a group of mammal-like reptiles evolved before
the dinosaurs. Although mammals did co-exist with dinosaurs, they did not
dominate their area until the dinosaurs went extinct. Then, the mammals that
survived the extinction rapidly diversified to fill the different environments on
Earth.
4. Student answers will vary. Data that would help resolve the overkill hypothesis
might include the discovery of large deposits of butchered extinct animals’ bones,
whose dates would coincide with the extinction of these organisms. Conversely, if
large deposits of extinct animals’ bones were found in areas with no signs of
human habitation, then scientists would have to rethink the overkill hypothesis.
Data that would support or refute the climate change hypothesis might be more
difficult, because climate changes would affect more organisms, instead of a
selective group (large North and South American mammals). If faunal and floral
data could show that the continents most affected by extinction had a more severe
climate change, this would support the hypothesis. Conversely, if data show that
the climate fluctuations on the continents most affected by the extinctions were
milder, this would help to refute the climate change hypothesis.
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