Weighing in at 200,000 kilograms and stretching the length of a basketball court, the blue whale is the biggest animal that’s ever lived.
蓝鲸重达20万公斤，有一个篮球场那么长，是有史以来最大的动物。
Now, scientists have figured out why they and other baleen whales got so huge.
如今，科学家们已经找到了它们和其他的须鲸如此庞大的原因。
“It’s a cool study,” says Jakob Vinther, an evolutionary paleobologist at the University of Bristol in the United Kingdom.
“这是一项很酷的研究，”英国布里斯托尔大学的进化古生物学家雅各布·温瑟尔说。
"I’m going to send it to my students."
“我要把它发给我的学生们。”
Biologists have long debated why some whales became the world’s biggest animals.
生物学家们很早就开始讨论为什么有些鲸鱼成为了世界上最大型的动物。
Some have proposed that because water bears the animal’s weight, whales can move around more easily and gulp in enough food to sustain big appetites.
有人提出这是因为水托起了它们的重量，所以鲸鱼可以轻松地移动，并吞下足够的食物来填饱自己的大胃口。
Others have suggested that whales got big to fend off giant sharks and other megapredators.
其他科学家则认为鲸鱼长这么大是为了抵御大型的鲨鱼和其他的大型捕食者。
Researchers have also argued about when these animals got so huge.
研究员们还争论着一个问题就是鲸鱼从什么时候开始变得如此巨大。
In 2010, Graham Slater, an evolutionary biologist currently at the University of Chicago in Illinois, argued that cetaceans—a term that includes whales and dolphins—split into different-sized groups very early in their history, perhaps 30 million years ago.
2010年，目前就职于伊利诺斯州芝加哥大学的进化生物学家格雷厄姆·斯莱特提出，鲸类——包括鲸鱼和海豚的一个术语——在其历史的早期就分裂成了不同大小的群体，可能是在3000万年前。
Dolphins remained the shrimps of the cetacean world, filter-feeding baleen whales became the giants, and predatory beaked whales stayed in the middle size-wise, with the descendants in those three groups sticking within those early established size ranges.
海豚仍然是鲸类动物世界的小虾米，滤食性长须鲸变成了庞然大物，而掠食性喙鲸的体型保持在中等大小，这三种鲸的后代都保持在早期确定的体型范围内。
However, Nicholas Pyenson, a whale expert at the Smithsonian Institution's National Museum of Natural History in Washington, D.C., was skeptical.
然而，华盛顿特区史密森学会国家自然历史博物馆的鲸鱼专家尼古拉斯.彭森说持怀疑态度。
So a few years ago, the two decided to tap the museum’s vast cetacean fossil collection to settle the dispute.
因此，几年前，两人决定利用博物馆收藏的大量鲸类化石来解决争端。
Pyenson had already surveyed living whale proportions and determined that the size of the whale correlated with the width of its cheek bones.
彭森已经调查了活鲸鱼的比例，并确定了鲸鱼的大小与其颧骨的宽度相关。
So Pyenson measured or obtained these data from skulls of 63 extinct whale species and of 13 modern species and plotted them on a timeline that showed the whale family tree.
所以，彭森从63种灭绝鲸鱼和13种现代鲸鱼的头骨中测量或获得了这些数据，并将它们绘制在显示鲸鱼家谱的时间轴上。
The data showed that whales didn’t get really big early on, as Slater had suggested.
数据显示，鲸类并没有像斯莱特所说的那样在早期就长得很大。
Nor did they gradually get big over time.
随着时间的推移，它们也没有逐渐变大。
Instead they become moderately large and stayed that way until about 4.5 million years ago, Slater, Pyenson, and Jeremy Goldbogen at Stanford University in Palo Alto, California, report today in the Proceedings of the Royal Society B.
相反，它们一直到大约450万年才变得相当巨大，位于加州帕洛阿尔托的斯坦福大学的斯莱特、宾森和杰里米·戈德博根在今天的《皇家学会学报B》上发表了一篇报告。
Then baleen whales went “from relatively big to ginormous,” Slater says.
然后长须鲸“从相对较大变成巨大，”斯莱特说。
Blue whales today are 30 meters long, where until 4.5 million years ago, the biggest whales were 10 meters long.
今天的蓝鲸有30米长，而450万年前，最大的蓝鲸只有10米长。
“The idea … that the shift … occurred so recently—4.5 million years ago—is surprising,” says Felisa Smith, a paleoecologist at the University of New Mexico in Albuquerque, who was not involved in the work but studies body size evolution.
新墨西哥大学阿尔伯克基分校的古生态学家费丽萨·史密斯说:“这种变化发生在距今如此近的时期—450万年前—的想法令人吃惊。”
Next, Slater and his colleagues checked to see what was happening in the world at the time to cause the change.
接下来，斯莱特和他的同事检查了当时世界上发生了什么导致了这种变化。
They found that the baleen whales' growth spurt coincided with the beginning of the first ice ages.
他们发现长须鲸的生长高峰与第一个冰河时代的开始是一致的。
As glaciers expanded, spring and summer runoff poured nutrients into the coastal ocean, fueling explosive growth in krill and small animals the whales consumed, they speculate.
他们推测，随着冰川的扩张，春夏两季的融水将营养物质注入沿海海洋，推动了鲸鱼所消耗的磷虾和小动物的爆炸性增长。
Until that time, prey had been uniformly distributed and plentiful, but the climate change caused many fish and big sea animals to disappear, and productivity plummeted.
在此之前，猎物分布均匀且数量充足，但气候变化导致许多鱼类和大型海洋动物消失，生物数量大幅下降。
That seasonal runoff created a new pattern of food availability: seasonal patches of very abundant food spaced far apart over the course of the year.
这种季节性融水创造了一种新的食物供应模式:在一年中，非常丰富的季节性的食物在地域上相隔很远。
Goldbogen helped Slater and Pyenson understand how that change was important.
戈德伯根帮助斯莱特和宾森理解了这种变化的重要性。
He studies whale eating and diving, and his work indicates that the more concentrated the food, the more efficient the feeding, especially in whales with really, really big mouths.
他研究鲸鱼的进食和潜水，他的工作表明，食物越集中，进食的效率就越高，特别是对于嘴非常非常大的鲸鱼。
Furthermore, larger whales can travel faster between patches of prey.
此外，体型较大的鲸鱼可以在猎物之间游得更快。
So baleen whales that got bigger, faster, thrived, whereas smaller species went extinct.
所以长须鲸变得更大，更快，更繁荣，而较小的物种则灭绝了。
And their giant size may have even promoted greater productivity, “by bringing up nutrients from deep waters as they dive and resurface,” suggests Geerat Vermeij, a paleobiologist at the University of California, Davis, who was not involved in the work.
加州大学戴维斯分校的古生物学家吉拉特.维尔梅伊没有参与这项研究，他说，“在它们潜水和重新浮出水面的过程中，会从深水中带出来营养”，它们巨大的体型甚至可能促进了更大的生物圈生产力。
This is not the first time researchers have decided that food has shaped whale evolution.
这不是研究人员第一次认为食物塑造了鲸鱼的进化。
But “the work helps us sort out the relative importance of different reasons why baleen whales got so big,” says Hans Thewissen, an anatomist who studies whales at Northeast Ohio Medical University in Rootstown and was not involved with the study.
但“这项工作帮助我们理清了长须鲸变大的不同原因的相对重要性，”解剖学家汉斯·特威森说，他在Rootstown的东北俄亥俄医科大学研究鲸鱼，没有参与这项研究。
“They elegantly and explicitly analyzed the data.”
“他们明确而清晰地对数据进行了分析”
“The study provides support for when and how the largest whales evolved,” Smith agrees.
史密斯对此表示赞同:“这项研究为大型鲸鱼的进化时间和方式提供了支持。”
However, although the timing of the shift seems to rule out that gigantism arose as a defense against megasharks and other predators prowling oceans at the time, she says, “I think there is enough uncertainty to remain somewhat skeptical” that the defense argument is dead.
然而，尽管这一转变的时机似乎排除了巨人症是作为一种防御当时在海洋中游荡的巨鲨和其他掠食者的手段出现的，她说，“我认为有足够的不确定性来保持某种程度上的怀疑”这种防御性论点是否说不通。
你是从什么时候开始感觉到春天到了呢
文中提到过的鲸鱼变得如此巨大的原因有哪些？
A.对付巨型捕食者
B.一直沿袭远古祖先的巨大体型
C.冰河时代冰川融水带来丰富食物
D.为了更快到达下一处进食点
留言回复正确选项即可获得红包哦，朋友们快来试试吧！
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