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  3. Once found almost entirely in the western United States and in Asia, dinosaur

Once found almost entirely in the western United States and in Asia, dinosaur

游客2023-12-16  7
问题   Once found almost entirely in the western United States and in Asia, dinosaur fossils are now being discovered on all seven continents. A host of new revelations emerged in 1998 that promise to reshape scientists’ views of dinosaurs, including what they looked like and when and where they lived.
  It is doubtful that Tyrannosaurus Rex had lips or that Triceratops had cheeks, says Lawrence Witmer, an assistant professor of anatomy at Ohio University in Athens, Ohio. He reached its conclusions by using high-tech computerized axial tomography (CT or CAT) scans along with comparative anatomy studies. For example, the theory that Triceratops and similar dinosaur species had cheeks was based on past comparisons with mammals such as sheep. But Witmer’s careful analysis found the structure of the triceratops jaw and skull made it more likely that Triceratops had a beak like that of an eagle. Witmer said that scientists should use birds and crocodiles as models when researching the appearance of dinosaurs.
  In early October scientists announced that they had confirmed the discovery of a new type of ceratopsian dinosaur. The dinosaur’s bones, found in New Mexico in 1996, are forcing paleontologists to rethink their theories about when ceratopsians migrated to what is now North America.
  Scientists previously thought that ceratopsians, the group that included the well-known Triceratops. arrived in North America from Asia between 70 million and 80 million years ago. During this time, the late Cretaceous Period. the earth’s two supercontinents—Laurasia in the north and Gondwanaland in the south—were in the process of pulling apart, cutting dinosaur populations off from each other and interrupting migratory patterns.
  The fossilized bones, found by paleontologist Doug Wolfe of the Mesa Southwest Museum in Arizona, date to about 90 million yeses ago. This could mean that ceratopsians originated in North America and migrated to Asia rather than the reverse, paleontologists said.
  An expedition from the Universities of Alaska in Anchorage and Fairbanks has discovered a region in remote northern Alaska so rich in fossilized dinosaur tracks that team members dubbed it the "dino expressway". The trampled area was found during the summer of 1998 on Alaska’s North Slope near the Brooks Range.
  The team found 13 new track sites and made casts from the prints of five different types of dinosaurs. The rock in which the prints were found dates to more than 100 million years ago, or about 25 million years older than the previously discovered signs of dinosaurs in the Arctic region. Paleontologists said that the new findings provide important evidence that dinosaurs migrated between Asia and North America during the early and mid-Cretaceous Period. before Asia split off into its own continent.
  Two rich fossil sites in the hills of Bolivia have been recently discovered, exciting paleontologists and dinosaur buffs. This discovery includes one of the most spectacular dinosaur trackways ever found.
  The discovery of a large site in the mountain region of Kila Kila in southern Bolivia was announced in early October. Here scientists found the tracks of at least two unknown species of dinosaur. These included a large quadruped (four. footed) dinosaur that was probably about 20 m (about 70 ft) long.
  The other site, located not far from the Bolivian city of Sucre, was uncovered in a cement quarry by workers several years ago but was not brought to paleontologists’ attention until the middle of 1998. The site features a vertical wall covered with thousands of dinosaur prints representing more than 100 different species. The tracks date back to between 65 million and 70 million years ago. Since dinosaurs are believed to have died out around 65 million years ago, the prints were likely made by some of the last dinosaurs on earth. Paleontologists hope to study the site and learn about the diet and physical characteristics of the dinosaurs that are represented there.  [br] Newly-found fossilized tracks in Alaska proved that dinosaurs’ migration between Asia and North America took place ______.
选项 A、much earlier than experts previously thought
B、much later than experts previously thought
C、after Asia became an independent continent
D、sometime around 25 million years ago
答案 A
解析 第四段说科学家认为ceratopsians从亚洲到达美洲是在70 million and 80 million years ago。第八段说“新发现的恐龙足迹存在于1亿年前，早于以前的发现”，最后一句说新的证据表明恐龙在亚洲和北美大陆之间迁徙是during the early and mid-Cretaceous Period(白垩纪中期)，before Asia split off into its own continent。由此可见恐龙在两块大陆之间的迁徙时间要比科学家以前设想还要早。
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