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Paragraph 1: It should be obvious that cetaceanswhales, porpoises, and dolphinsare mammals. They breathe through lungs, not through gills, and give birth to live young. Their streamlined bodies, the absence of hind legs, and the presence of a fluke3 and blowhole4 cannot disguise their affinities with landdwelling mammals. However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. Extinct but, already fully marine cetaceans are known from the fossil record. How was the gap between a walking mammal and a swimming whale bridged? Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.
1. In paragraph 1, what does the author say about the presence of a blowhole in cetaceans? ○It clearly indicates that cetaceans are mammals. ○It cannot conceal the fact that cetaceans are mammals. ○It is the main difference between cetaceans and landdwelling mammals.
○It cannot yield clues about the origins of cetaceans.
2. Which of the following can be inferred from paragraph 1 about early sea otters? ○It is not difficult to imagine what they looked like
○There were great numbers of them.
○They lived in the sea only.
○They did not leave many fossil remains.
Paragraph 3: The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossil provides precious details on the origins of cetaceans. The skull is cetaceanlike but its jawbones lack the enlarged space that is filled with fat or oil and used for receiving underwater sound in modern whales. Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesheating mammals, the mesonychids, and cetaceans. It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean. It probably bred and gave birth on land.
3. The word precious in the passage is closest in meaning to ○Exact ○Scarce
4. Pakicetus and modern cetaceans have similar ○Hearing structures ○Adaptations for diving
5. The word it in the passage refers to ○Pakicetus
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Paragraph 4: Another major discovery was made in Egypt in 1989. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert. This whale lived around 40 million years ago, 12 million years after Pakicetus. Many incomplete skeletons were found but they included, for the first time in an archaeocyte, a complete hind leg t...
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- Fall '13