Biology

When and why whales evolved to be so huge

When and why whales evolved to...
Researchers have traced the evolution of whales back a few million years, and found that their size increased rapidly in response to changing climates
Researchers have traced the evolution of whales back a few million years, and found that their size increased rapidly in response to changing climates
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Researchers have traced the evolution of whales back a few million years, and found that their size increased rapidly in response to changing climates
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Researchers have traced the evolution of whales back a few million years, and found that their size increased rapidly in response to changing climates

The blue whale may be the largest animal to have ever existed, but new research has found that the species only claimed the title relatively recently. By comparing the bones of modern whales to fossils from extinct species, a team of scientists from Stanford, the University of Chicago and the Smithsonian has traced the growth spurt of baleen whales to about 4.5 million years ago, when climate change increased the food supply.

For most of their 30-million year evolutionary history, baleen whales have been relatively small, capping out at about 10 m (33 ft) in length. The researchers found that whales as big as today's behemoths, which can measure up to 30 m (100 ft) in the case of the blue whale, began appearing fairly rapidly about 3 million years ago, and they wanted to know why.

The first challenge was to find a way to accurately determine the size of extinct species, given the somewhat patchy fossil record. Working with more complete modern skeletons, the researchers found that the width of a whale's skull could be a good starting point to calculate the length of its body. Using this system, they examined skulls from the Smithsonian's collection and worked out the length of 63 extinct whale species.

According to the team's findings, the uptick in whale sizes really took off about 4.5 million years ago. Around that time, something shifted in the ecosystem that drove a two-pronged path towards gigantism, causing bigger animals to start appearing in different lineages, while the smaller species started dying off.

"We might imagine that whales just gradually got bigger over time, as if by chance, and perhaps that could explain how these whales became so massive," says Graham Slater, co-author of the study. "But our analyses show that this idea doesn't hold up — the only way that you can explain baleen whales becoming the giants they are today is if something changed in the recent past that created an incentive to be a giant and made it disadvantageous to be small."

The change seems to line up with the beginning of an Ice Age, and the researchers suggest that the changing climate would have benefitted baleen whales' feeding habits of filtering krill out of water. As new ice caps formed, nutrients would have seasonally been washed into coastal waters, increasing the food supply. According to previous research on modern whales, filter-feeding is even more efficient in larger species, so nature would have favored the bigger baleens at the time.

As an added bonus, the larger animals would be better equipped for thousand-mile migrations, to take advantage of seasonal shifts in the food supply.

"An animal's size determines so much about its ecological role," says Nicholas Pyenson, co-author of the study. "Our research sheds light on why today's oceans and climate can support Earth's most massive vertebrates. But today's oceans and climate are changing at geological scales in the course of human lifetimes. With these rapid changes, does the ocean have the capacity to sustain several billion people and the world's largest whales? The clues to answer this question lie in our ability to learn from Earth's deep past — the crucible of our present world — embedded in the fossil record."

The study was published in the journal Proceedings of the Royal Society B.

Source: Smithsonian

9 comments
KeithMoat
Cannibalism, big fish (mammal in this case) eat little fish.
ClarkMagnuson
"today's oceans and climate are changing at geological scales in the course of human lifetimes." That's ain't science, that is religion.
f8lee
@Keith - baleen whales don't have teeth - the "baleen" part refers to the filtration system in their mouths - they eat by sucking in huge quantities of water and pressing it out through the filter (baleen) to retrieve the frill and other plankton - all of which are tiny creatures. They quite literally cannot eat fish. That said, "cannibalism" refers to the concept of eating one's own species - so even that term is completely wrong in this regard.
Michael Z. Williamson
Keith: Cannibalism is eating one's own species, not another. And all the baleen whales are filter feeders, not predators. However, even if we ignore human warming factors, geologically, the Earth should continue to warm over the next 15 million years as tectonics force the end of glaciation. This means whales should evolve smaller again.
ezeflyer
The end of the whaling industry is likely to have allowed large whales to survive. And whaling countries like Japan and Norway may be going after smaller species.
Koolski
There is one huge supposition here. You can't assume things like "the width of a whale's skull could be a good starting point to calculate the length of its body" for anything other than today's whales. Since they are evolving, their overall shape may changing too -- like the size of their head.
JimFox
ClarkMagnuson Your comment ain't science but rather ignorance.
chase
Interesting hypothesis/theory of it was indeed a growth spurt. But there's holes in the theory that are easy refuted. Abundance of a food source doesn't make for a gene change. A requirement for an overall physical change within a species. A dramatic gene change would suggest another cause. Change in water chemistry perhaps. The change, the cause. The effect, the need to migrate great distances to accommodate the change. In this case, size. Their theory presents a which came first, the chicken or the egg. They, the large filter whales, may have just gotten lucky. That their physical change came about at a time of abundance in a food source. One they could take advantage of, while food sources for other species may have been in short supply. Just a thought...
GeneWaldenmaier
Evolved ... what is so unique about the whale's DNA's size and complexity relative to the DNA of every living cell that every existed? How did that first DNA evolved with no trace. How did the programs within those cells along with the execution files to run those cells evolve. The building blocks of DNA had to be from the particles found in molecules and they from atoms ...from subatomic particles ... but all so precise that scientist still can not measure the variance within the grouping of each of matter's "building blocks". Evolved...in deed.