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OFFICIAL27 Why does the professor discuss gastroliths that have been found with sauropod fossils?

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[00:00.00]NARRATOR: Listen to part of a lecture in a zoology class.[00:03.35]FEMALE PROFESSOR: Your reading for today touched on dinosaur fossils from the Mesozoic era [00:10.79]Today, we'll be discussing the sauropods.[00:13.68]I think our discussion of sauropods will illustrate what we can learn by comparing the fossil record to [00:21.65]By "fossils,"we mean traces of prehistoric animals–such as bones, which become mineralized ...or impressions of bones or organs that're left in stone...[00:31.30]Now, sauropods were among the largest animals to exist, ever. [00:35.45]They were larger than blue whales, which are the [00:39.78]they weighed up to 100 tons–20 times as much as elephants. [00:45.01]Also, they were an [00:48.49]there's evidence of sauropods in the fossil record for an [00:55.51]So: Why were sauropods so successful?
[00:58.89]Biologically speaking, sauropods shouldn't have been successful. [01:03.52]Large animals–like [01:11.83]this makes maintaining a population harder. [01:14.93]The largest animals today don't live on land,
[01:18.27]but [01:26.13]and they give birth only once every few years. [01:28.93]We also know that body heat–that ...uh, well ...large [01:37.14]but for an ocean-going whale, that's not a problem; [01:40.33] for a 100-ton land animal, it can be.
[01:43.61]For years we've assumed it was the abundant plant life of the Mesozoic that allowed these giants to [01:50.58]However, we now know that, since oxygen levels were much lower in the Mesozoic than we'd [02:01.78]So now? well, we're looking at other–we...we're-we're trying to understand the biology of sauropods, comparing their fossils to the [02:15.51]What we've found is that sauropods were experts at conserving energy.
[02:21.81]They had enormous stomach capacity–the ability to digest food over a long period...converting it to energy at a slower [02:31.71]For animals with small stomachs, it takes lots of energy to constantly [02:38.04]with larger stomachs and slower digestion, you don't need as much [02:45.01]MALE STUDENT: Does ...mm, do scientists actually know about [02:59.36] ... and comparisons between animals that lived millions of years apart–[03:03.41]w-well, it just seems ...more like guessing.
[03:06.89]FEMALE PROFESSOR: [03:11.12]There's always guesswork when studying extinct animals; but [03:17.05]we "test" the hypothesis, by [03:21.03]then some questions are answered, which may lead to new question...[03:25.65]For example: Let's look at one of these comparisons?
[03:29.34] We know sauropods couldn't chew food–[03:32.72]their skulls show they had no chewing muscles. [03:35.41]Lots of modern animals–like birds and [03:40.48]they need to swallow it whole. [03:42.33]But modern animals have an interesting aid for [03:46.66]They swallow stones ...stones that're used to help grind up the food ...before it's actually [03:54.67]These stones are called "gastroliths."[03:57.85]Gastroliths make food easier to digest, [04:06.06]Over time, gastroliths inside the animal are ground [04:12.19]Now, sauropod fossils are commonly found with smoothed stones...[04:17.11]for years, [04:19.87]they looked just like gastroliths, and were found in the area of the [04:24.54]A recent study measured the gastroliths in modern animals–in ostriches ...[04:30.72]and the study showed that [04:37.24]But we've been able to determine [04:47.14]So now, we're not quite sure what these sauropod stones were used for. [04:51.77]It could be they were [04:58.88]Other [05:06.83]So, the original hypothesis–that the stones found with sauropods were gastroliths–even though it

5.Why does the professor discuss gastroliths that have been found with sauropod fossils?

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原文出处:Professor: But modern animals have an interesting aid for digesting food. Professor: They swallow stones, stones that are used to help grind up the food before it’s actually digested in the stomach. Professor: These stones are called gastroliths. Professor: Gastroliths make food easier to digest, essentially smashing food up, just as we do when we chew. Professor: Over time, gastroliths inside the animal are ground down and become smooth and rounded. Professor: Now, sauropod fossils are commonly found with smooth stones. Professor: For years we thought these were gastroliths. Professor: They looked just like gastroliths and were found in the area of the sauropods’ stomachs. Professor: A recent study measured the gastroliths in modern animals, in ostriches. Professor: And the study showed that ostriches need to ingest about one percent of their total body weight in gastroliths. Professor: But we have been able to determine that the stones found with sauropods total much less proportionally, less than a tenth of one percent of their body weight. Professor: So now we are not quite sure what these sauropods’ stones were used for. Professor: It could be they were accidentally ingested as the sauropods foraged for food, that they served no real purpose. Professor: Other researchers speculate that sauropods ingested these stones as a source of some of the minerals they needed, such as calcium. Professor: So the original hypothesis that the stones found with sauropods were gastroliths, even though it hasn’t been supported, has helped us to make new hypotheses, which may eventually lead to the answer. 解析:But we have been able to determine that the stones found with sauropods totaled much less proportionally, less than a tenth of one percent of their body weight. 教授举了gastroliths的例子,来证明guesswork可以引导研究,找到答案,再发现新的问题。这和B选项表达的意思呼应。

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