文章大意:本文是一篇说明文。文章介绍了大熊猫的特殊食性和其拥有的“伪拇指”,并探讨了这种特殊的进化方式。大熊猫以竹子为食,每天需要吃30磅,而它们的“伪拇指”帮助它们紧紧抓住竹子。研究人员发现,大熊猫的祖先Ailurarctos在600万到700万年前就已经拥有了这种特殊的骨骼结构,并开始食用竹子。这种“伪拇指”没有进化成真正的拇指,因为这样会影响大熊猫的行走。
For such a big bear, the giant panda’s favorite food, bamboo, is surprising. It’s a tough, stick-like plant with relatively few nutrients, so the panda has to eat it all day long just to sustain itself. That amounts to about 30 pounds a day for a 300-pound panda. How do they do it?
The answer is in their paws. Each one has a sixth finger, which scientists call a “pseudo-thumb”. It is actually an extension of the panda’s wrist bone. “It’s not nearly as good a thumb as ours, so they can’t make tools or complex movements,” said Wang Xiaoming, a scientist who studies fossils at the Natural History Museum of Los Angeles County in California. But the pseudo-thumb is shaped like a hook(挂钩), and it helps the bear tightly grasp stalks(秆)of bamboo as it chews them.
For many years, researchers have wondered how the pseudo-thumb evolved(进化). Very few fossils of panda paws have been found, so the earliest evidence scientists could find was from about 150,000 years ago. But in 2015, Wang and his team discovered a spoon-shaped piece of bone belonging to Ailurarctos, an ancestor of modern pandas that lived in the Miocene Epoch, about 6 million to 7 million years ago. While some primitive(原始的)animals also had big wrist bones, Ailurarctos seemed to be one of the first animals to actually use its pseudo-thumb.
Researchers believe that in a crowded forests, where Ailurarctos had to vie with ancient elephants, apes, and deer for food. Being able to eat bamboo helped the bear stay alive. Bamboo was available in large quantities and it grew quickly, so the bears could snack on the plant as much as they wanted.
The team thinks that the beneficial bone never evolved into a real thumb because it would be too difficult for a panda to walk on all four paws without pressing a larger finger. “We think the pseudo-thumb is an evolutionary balancing act,” Wang said. “Pandas need it for grasping, but they also keep stepping on it.”
8. What is the function of the “pseudo-thumb”?
A.It benefits pandas’ walking. |
B.It can turn the food easily like a real thumb. |
C.It can only make simple movements and tools. |
D.It helps the five existing fingers hold bamboo tightly. |
9. What does the underlined word “vie” in Paragraph 4 mean?
A.Deal. | B.Work. |
C.Compete. | D.Connect. |
10. What has been found by researchers according to the text?
A.The “pseudo-thumb” has evolved for 150,000 years. |
B.A panda’s real thumb will come into being. |
C.Quite a few fossils of panda paws have been found. |
D.The “pseudo-thumb” is an evolutionary result. |
11. Where is this text probably taken from?
A.An animal story. | B.A nature textbook. |
C.A science magazine. | D.A news report. |