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更新时间:2017-5-30 8:02:39 来源:纽约时报中文网 作者:佚名

How Whales Became the Biggest Animals on the Planet

Whales are big. Really big. Enormously big. Tremendously big.


Fin whales can be 140,000 pounds. Bowhead whales tip the scales at 200,000 pounds. And the big mama of them all, the blue whale, can reach a whopping 380,000 pounds — making it the largest animal to have ever lived.


But for as long as whales have awed us with their great size, people have wondered how they became so colossal.


In a study published Tuesday in the journal Proceedings of the Royal Society B, a team of researchers investigated gigantism in baleen whales, the filter-feeding leviathans that include blue whales, bowhead whales and fin whales. The marine mammals became jumbo-size relatively recently, they found, only within the past 4.5 million years. The cause? A climatic change that allowed the behemoths to binge-eat.

周二,在一项发表在《英国皇家学报》B辑(Proceedings of the Royal Society B)的研究中,一组研究人员对须鲸科的“巨人症”进行了研究,这一滤食性庞然大物包括蓝鲸、弓头鲸及长须鲸。研究人员发现,这种海洋哺乳动物是在较为近期,仅在过去450万年间才变成巨无霸的。原因?一场导致这种巨型生物大量进食的气候变化。

Whales have an interesting evolutionary history. They began as land-dwelling, hoofed mammals some 50 million years ago. Over several millions of years they developed fins and became marine creatures. Between about 20 million and 30 million years ago, some of these ancient whales developed the ability to filter-feed, which meant they could swallow swarms of tiny prey in a single gargantuan gulp. But even with this feeding ability, whales remained only moderately large for millions of years.


“But then all of a sudden — ‘boom’ — we see them get very big, like blue whales,” said Nick Pyenson, the curator of fossil marine mammals at the Smithsonian Institution’s National Museum of Natural History and an author of the paper. “It’s like going from whales the size of minivans to longer than two school buses.”

“但突然间——‘轰’地一下——它们变得非常巨大,比如蓝鲸”,史密森尼学会国立自然历史博物馆(Smithsonian Institution’s National Museum of Natural History)策展人、该论文的作者尼克·佩尔森(Nick Pyenson)说。“鲸鱼的体型变化就像从小货车变得比两个校车还大。”

Dr. Pyenson and his colleagues measured more than 140 museum specimens of fossilized whales, and then plugged that data into a statistical model. It showed that several distinct lineages of baleen whales became giants around the same time, independently of one another. Starting around 4.5 million years ago, giant blue whales were popping up in oceans across the world alongside giant bowhead whales and giant fin whales.


The researchers suspected that an environmental change happened during that time that essentially caused the baleen whales to bulk up. After some investigation, they found that this time period coincided with the early beginnings of when ice sheets increasingly covered the Northern Hemisphere.


Runoff from the glaciers would have washed nutrients like iron into coastal waters and intense seasonal upwelling cycles would have caused cold water from deep below to rise, bringing organic material toward the surface. Together these ecological effects brought large amounts of nutrients into the water at specific times and places, which had a cascading effect on the ocean’s food web.


Throngs of zooplankton and krill would gather to feast on the nutrients. They would form dense patches that could stretch many miles long and wide and be more than 65 feet thick. The oceans became the whales’ giant all-you-can-eat buffets.


“Even though they had the anatomical machinery to filter-feed for a long, long time,” said Jeremy Goldbogen, a comparative physiologist from Stanford University and author of the paper, “it wasn’t until the ocean provided these patchy resources that it made bulk filter-feeding so efficient.”

“尽管它们有着能够长期滤食的生理结构,”斯坦福比较生理学家、论文作者杰里米·戈登伯根(Jeremy Goldbogen)说,“直到海洋提供了这些大片资源,才使得大量滤食如此有效。”

The baleen whales could now gulp down much larger amounts of prey, which allowed them to get bigger. But that was only part of the equation.


“Plentiful food everywhere isn’t going to get you giant whales,” said Graham Slater, an evolutionary biologist at the University of Chicago and the study’s lead author. “They have to be separated by big distances.”

“到处都是充足的食物是无法让让鲸鱼变成巨型的,”芝加哥大学进化生物学家格雷厄姆· 斯莱特(Graham Slater)、论文的主要作者说。“必须被遥远的距离分隔开才行。”

Because the ecological cycles that fuel the explosions of krill and zooplankton occur seasonally, Dr. Slater said the whales must migrate thousands of miles from food patch to food patch. Bigger whale ancestors that had bigger fuel tanks had a better chance of surviving the long seasonal migrations to feed, while smaller baleen whales became extinct.


If the food patches were not far apart, Dr. Slater said, the whales would have grown to a certain body size that was comfortable for that environment, but they would not be the giants we see today.


“A blue whale is able to move so much further using so much less energy than a small-bodied whale,” Dr. Slater said. “It became really advantageous if you’re going to move long distances if you’re big.”