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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2023-12-17  21
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. Witmer was a leading researcher for a study on dinosaur anatomy that was presented at the annual meeting of the Society for Vertebrate Paleontology, which concluded on October 3 in Snowbird, Utah.
   Witmer’s study reached its conclusions by using high-tech computerized axial to mograply (CT or CAT) scans along with comparative anatomy studies. For example, the theory that Triecratops and similar dinosaur species had cheeks was based on past comparisons with mammals such as sheep. But Witmer’s carful 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 ceratopsiaus 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 Gretaceous 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 eight-year-old Christopher Wolfe and his father, paleontologist Doug Wolfe of the Mesa Southwest Museum in Arizona, date to about 90 million years ago. This could mean that ceratopsians originated in North America and migrated to Asia rather than the reverse, paleontologists said. Doug Wolfe named the important new species of dinosaur Zuniceratops christopheri after his son.
   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 in 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-foot-ed) dinosaur that was probably about 20m (about 70ft.) 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.
   Scientists speculated that the tracks were made at the edge of a lake or swamp and were then hardened and preserved. The rock containing the tracks was then pushed into a vertical position over millions of years of geologic activity. Dinosaur eggs have also been found at the site, which paleontologists are working to preserve before it falls victim to erosion. 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 该题问：在阿拉斯加新近发现的化石痕迹证明恐龙在亚洲和北美之间的迁移发生在什么时候?A项意为“比专家以前想的要早得多”；B项意为“比专家以前想的要晚得多”；C项意为“亚洲成为独立的大陆之后”；D项意为“两千五百年前左右的某个时候”。第八段中的第二句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 。表明在阿拉斯加发现的恐龙痕迹是一亿年以前的，而第八段的最后一句说该发现提供了重要的证据表明亚美大陆之间的恐龙迁移发生在cretaeeoll8(白垩纪)时代的早中期。结合上文讲到白垩纪末期在七千至八千万年前，可以确信，该发现证明这种迁移发生的时间早于以往专家们认为的时间。
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