评论
打印
Listen to part of a lecture in a zoology class.
听一段动物学课程。
Your reading for today touched on dinosaur fossils from the Mesozoic era, which ended about 65 million years ago.
你们今天的阅读材料讲的是中生代时期的恐龙化石，中生代在六千五百万年前结束。
Today we will be discussing the sauropods.
今天我们要讲的是蜥脚类动物。
I think our discussion of sauropods will illustrate what we can learn by comparing the fossil record to modern animals.
我认为，我们对蜥脚类动物的讨论能告诉我们，将化石和现代动物对比，我们能学到什么。
By fossils, we mean traces of prehistoric animals such as bones, which become mineralized, or impressions of bones or organs that are left in stone.
化石是指史前生物的遗迹，比如已经矿化的骨头和骨头或器官在石头上留下的印记。
Now sauropods were among the largest animals to exist ever!
有史以来，在存在过的动物中，蜥脚类动物是体型最大的。
They were larger than blue whales, which are the largest animals alive today.
它们比蓝鲸还大，而蓝鲸是现存动物中最大的。
They weigh up to one hundred tons, twenty times as much as elephants.
蜥脚类动物体重能达到100吨，是大象体重的二十倍。
Also, they were an extremely successful kind of dinosaur.
并且它们作为恐龙而言是很成功的。
There's evidence of sauropods in the fossil record for an unusually long time, over one hundred million years.
有化石证据显示，蜥脚类动物的存在时间长得有些不寻常，超过了一亿年。
So, why were sauropods so successful?
为什么蜥脚类动物这么成功？
Biologically speaking, sauropods shouldn't have been successful.
从生物学角度来看，蜥脚类动物不应该这么成功。
Large animals like elephants, say, they require much more food and energy and have fewer offspring than smaller animals.
大型动物（如大象）比起体型更小的动物而言，需要更多的食物和能量，而后代更少。
This makes maintaining a population harder.
这就使维持一定的种群数量变得更加困难。
The largest animals today don't live on land, but in the ocean where food is easier to find.
现在，体型最大的动物不生活在陆地上，而是生活在更容易觅食的海洋里。
A blue whale, for instance, can eat up to 8,000 pounds of food a day.
举个例子，一只蓝鲸一天能吃掉八千磅的食物。
And they give birth only once every few years.
而且它们每隔几年才繁衍一次。
We also know that body heat, that… well, large animals can't easily get rid of excess body heat.
我们还知道体温……大型动物不容易散去多余体温。
But for an oceangoing whale, that's not a problem.
对于在海里生活的鲸鱼来说，这不是问题。
For a 100-ton land animal, it can be.
但对于一百吨的陆生生物而言，就是个问题了。
For years, we have assumed it was the abundant plant life of the Mesozoic that allowed these giants to thrive.
多年来，我们都以为，是中生代时期的丰富植物让这些巨型动物繁荣起来。
However, we now know that since oxygen levels were much lower in the Mesozoic than we assumed, there was much less plant life for sauropods to eat than we thought.
但我们现在知道了，由于中生代的氧气含量比我们所以为的要低得多，在那时候并没有我们想象中那么多的植物供蜥脚类动物食用。
