1. The Mammals that Conquered the Seas
Current Issues in Biology, Volume 2
Scientific American

2. The Mammals that Conquered the Seas
Concept Review
Fossil evidence indicates that vertebrates originated in
aquatic environments and later adapted to land.
Mammals originated on land. But some mammals, such as whales, later adapted to marine environments, reversing the trend.

3. The Mammals that Conquered the Seas
Concept Review
Whales may live in water, but they are not fish.
They are clearly warm-blooded mammals, breathing air
and nursing their young. Along with dolphins and porpoises,
they belong to an order of mammals called cetacea.
The whales’ return to water was poorly understood until fossil discoveries over the last two decades helped trace their transition.

4. The Mammals that Conquered the Seas
Concept Review
This shift occurred during the Eocene era, about 55
to 34 million years ago.
Archaic whales, or archaeocetes, may have been drawn
back to aquatic life by ancient seas teeming with food.

5. The Mammals that Conquered the Seas
Concept Review
Whales’ transitional ancestors had characteristics of both
land and sea creatures – legs and hooves for walking, tails
for swimming.

6. The Mammals that Conquered the Seas
Concept Review
Scientists once thought whales might be descended from
extinct wolf-like hoofed mammals called mesonychids.
But later fossil and molecular studies suggest closer ties
to artiodactyls, even-toed hoofed mammals such as
camels and pigs.
The hippopotamus may be an especially close whale
relative.

7. The Mammals that Conquered the Seas
Testing Your Comprehension
Distant ancestors of whales had what characteristics?
a) fur
b) milk-producing glands
c) legs and feet
d) all of the above

8. The Mammals that Conquered the Seas
Testing Your Comprehension
Distant ancestors of whales had what characteristics?
d) all of the above

9. The Mammals that Conquered the Seas
Testing Your Comprehension
Whales are most closely related to which terrestrial mammals?
a) artiodactyls such as camels, pigs, and cows
b) carnivores such as bears, raccoons, and otters
c) perissodactyls such as horses, donkeys, and zebras
d) all of the above

10. The Mammals that Conquered the Seas
Testing Your Comprehension
Whales are most closely related to which terrestrial mammals?
a) artiodactyls such as camels, pigs, and cows

11. The Mammals that Conquered the Seas
Testing Your Comprehension
Which of the following do not help explain how modern whales
fit into the mammalian family tree?
a) DNA analysis
b) the fossil record
c) modern whale anatomy
d) antibody-antigen physiology

12. The Mammals that Conquered the Seas
Testing Your Comprehension
Which of the following do not help explain how modern whales
fit into the mammalian family tree?
c) modern whale anatomy

13. The Mammals that Conquered the Seas
Testing Your Comprehension
Which of these is not thought to be an ancestor of modern
whales?
a) Basilosaurus
b) Ambulocetus
c) Orca
d) Dorudon

14. The Mammals that Conquered the Seas
Testing Your Comprehension
Which of these is not thought to be an ancestor of modern
whales?
c) Orca

15. The Mammals that Conquered the Seas
Biology and Society
Selective pressures in the Eocene environment caused whales
to adapt and return to water. Environmental pressures
are also driving natural selection in the present-day world.
Strongly
Agree
Disagree A. E. C. B. D.

16. The Mammals that Conquered the Seas
Biology and Society
During the Eocene era, ancient oceans covered much of what
is now the Indian subcontinent, including Pakistan. Important
whale ancestor fossils have been found there, but such work
has also been interrupted by modern-day conflict. Scientists
should receive special protection to conduct research globally,
despite political or social problems.
Strongly
Agree
Disagree A. E. C. B. D.

17. The Mammals that Conquered the Seas
Thinking About Science
Most mammals cannot live without fresh water. But cetaceans obtain their water, in part, from sips of the salty ocean. To investigate when the ancestors of whales became able to ingest seawater, scientists applied a technique to measure the ratio of certain oxygen isotopes in fossilized teeth. The ratio of these isotopes is different in fresh and salt water.
Describe how this difference helped shape the hypothesis of the scientists conducting the research.

18. The Mammals that Conquered the Seas
Interpreting Data and Graphs
These drawings illustrate how various hypotheses of whale
ancestry have changed as new findings come to light.
According to each of the four drawings, which category of
creature is the whale’s closest relative?