托福

关于2018年11月24日的托福听力考试，想必大家都非常感兴趣，那么今天就跟着出国留学网来看看2018年11月24日托福听力考试机经。

题目

is the lecture mainly about

hypotheses about dinosaurs resulting from tissue analysis ors that allow dinosaur bones to be well preserved

role of histology in determining nutritional needs of dinosaurs

identification of some recently discovered dinosaur bones

2. hy does the professor describe the process of petrifaction？  clarify the difference between bone and soft tissue

explain why histology can be used on dinosaur bones  remind students of how long ago dinosaurs lived  describe the origins of some cracks in dinosaur bones

3. hat would researchers have concluded if they had found stress-fractures in the skulls of certain dinosaurs

they had been undernourished

they had engaged in head butting behavior  the skull bones were not well preserved  the skull bones were fragile

4. According to the professor， what evidence supported the original hypothesis that Apatosaurus took decades to reach its adult size

Click on 2 answers.

t bones had many growth rings.

B. Its environment did not support many plants.

C. It was a very large animal. rn day reptiles grow slowly.

5. rior to the use of histological analysis， what would researchers have probably concluded upon the discovery of the bones of a small sauropod？

bones belonged to a new species of sauropod.  bones belonged to a dwarf species of dinosaur.  dinosaur＇s habitat had limited resources.

bones belonged to an immature dinosaur.  does the professor say this：

suggest a reason that the dinosaur did not survive

find out if the students believe such rapid growth was possible  express her sense of amazement

show how inaccurate researchers were in their original prediction

　　听力文本

Narrator：

Listen to part of a lecture in a biology class. Professor：

We have very good ideas about the various shapes and sizes of dinosaurs from studying their petrified bones. But we’ve had to hypothesize about things like their behaviors and lifespan because much of that kind of information isn’t preserved the way bones and teeth are， or so we thought. Now， just to review a second， the

dinosaur bones we studied were preserved and turned to stone millions of years ago through the process of petrifaction. Petrifaction is when all of the original biological material gets replaced with minerals without losing its original shape or details. Some petrified dinosaur bones contain almost perfectly preserved microstructures as small as individual cells. And when bones are that well preserved， we can use histology to examine them. Histology is the study of biological tissue. And in this case，

histology is being used to study petrified bone tissue. To do that， the petrified bone has to be cut into slices so thin that light can pass through

them. Then you can examine them under a microscope. It turns that the

preserved microstructures contains a lot of information， including clues to behavior.

In fact， long-standing hypotheses about dinosaur behavior are being proved wrong and new hypotheses about dinosaur behavior are taking their place. For example， there’s one dinosaur that we know had a high dome-shaped skull composed of thick bone. Since the 1950s， we thought that with such a thick skull that males probably butted heads just like big-horn sheep do today， probably when competing for mates. But just a couple of years ago， some university researchers in the United States took a close look at the histological findings in several of these skulls to look for evidence of head butting like healed cracks or stress fractures. But the analysis clearly showed that there was no sign of that kind of stress to the

bones. Instead， what they found was small structures that look like they may have actually anchored a crest to the skull.

Female： Professor：

A crest， maybe like a rooster comb？

So now paleontologists are wondering what the crest might have

been used for. Display？ Recognition？ But certainly not for head butting.

Now， another long-standing hypothesis was that the really big dinosaurs took decades to reach full size. After all， they hatched some fairly small eggs and they had a lot of growing to do so it’s a fairly logical assumption that it took a long time to reach their giant sizes. Then researchers did a histological examination of Apatosaurus’ bones. Apatosaurus was a species of sauropod， a giant plant-eating dinosaur. It had a long neck and a long tail and its full size was about 25 meters long and weighed about 25 tons. Now， the idea that the Apatosaurus grew slowly was based on many observations including its enormous size and the fact that large modern reptiles grow slowly. For example， Apatosaurus has a relatively small mouth and simple feet and the plants that lived at that time were not particularly nutritious. Altogether， it’s not a recipe for fast growth. However， under a microscope， it’s clear that dinosaur bones have growth rings and by counting them like tree rings， paleontologists can infer how many years of bones have grown. And when comparing the growth rings from several specimens of the same species of dinosaur， paleontologists can figure out growth rate for that species. Well surprisingly， that giant Apatosaurus reached its full size in just eight to eleven years. Just eight to eleven years！ Can you imagine

growing three meters a year？ And the only way information like this can

be worked out is through histology， you know？

And if that isn’t enough， histology has recently revealed another surprise. In Germany， the bones of several small sauropods were found in a quarry. Some sauropods grew to be very large. The discovery of small sauropod bones usually means you have found juveniles， young ones. But the histological evidence showed that the bones were from a species of dwarf sauropods that only grew to six meters long and matured in just three years. The new hypothesis is that these dinosaurs evolved to be small because they lived on an island with limited resources.