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

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.

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.

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.

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.

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.

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

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

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

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

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

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

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

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

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.

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.

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.

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?