Why Did Whales Get So Big?

SCIENCE

According to new research, it was only recently in whales’ evolutionary history that they became so enormous. (Smithsonian)

Use our activity to size yourself up to a blue whale!

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit.

The ancestors of this big, beautiful blue whale were only about 6 meters (20 feet) long. Today, blues can reach more than 33 meters (110 feet).
Photograph by NOAA. CC-BY-2.0

Click to zoom in! Can you spot the long-and-lean baleens? This “Whales of the World” poster was printed in National Geographic magazine in 1976.
Map by Larry Foster, National Geographic

Discussion Ideas

  • A new study analyzes the evolution of baleen whales. What are baleen whales?

 

  • When did baleen whales get so big?
    • Well, not all baleen whales are giants. The smallest baleen whale, the pygmy right whale, is about 6 meters (20 feet) long.
    • The big baleens, such as blue, fin, and sei whales, increased in size during an ice age, about 3-4 million years ago. (On an evolutionary time scale, that’s just recently.)

 

  • Why did baleen whales get so big?
    • Climate change forced a radical alteration in their food supply.
      • During the glacial period, “the planet entered a cycle where large glacial sheets would form in the northern hemisphere, expand all the way down to the northern U.S., and then retreat again. These cycles triggered a shift away from continuous warmth toward seasonal climates that varied over the year. That seasonality reshaped the oceans. By strengthening winds that blow from the south, it intensified the upwelling currents that bring nutrients up from the depths, specifically near the coasts of continents. And those coastal waters were also hit by run-offs from melting glaciers on land, which brought even more nutrients with them.”
      • At the time of this transition, [filter-feeding] baleen whales … were well equipped to take advantage of these dense patches of food. … What’s more, large whales can migrate thousands of miles to take advantage of seasonally abundant food supplies. So, the scientists said, baleen whales’ filter-feeding systems, which evolved about 30 million years ago, appear to have set the stage for major size increases once rich sources of prey became concentrated in particular locations and times of year.”
        • Baleen whales such as blues and humpbacks still migrate enormous distances every year.

 

  • Why are we only now gaining greater understanding about how whales evolved?
    • The same reason we don’t have better understanding about the evolutionary history of most species—an incomplete fossil record. “We haven’t had the right data,” says one researcher. “How do you measure the total length of a whale that’s represented by a chunk of fossil?” (Good point.)

 

  • How did scientists conduct the study of the evolution of whale size?
    • Researchers recently “established that the width of a whale’s skull is a good indicator of its overall body size.” With this correlation, they could conduct their analyses.
      • Researchers measured fossil skulls to estimate the size of 63 extinct species of baleen whale. They also gathered data from 13 extant (still-living) species of baleens.
        • Specimens ranged from the earliest baleen whales, about 30 million years old, to species that are alive and well today. This provided a broad sample of whale size before and after the last ice age.

 

TEACHERS TOOLKIT

Smithsonian: Only Recently Did Whales Become Giant

The Atlantic: Why Did the Biggest Whales Get So Big?

Nat Geo: Size Me Up—to a Blue Whale!

Understanding Evolution: The evolution of whales

Wikipedia: Baleen Whales featured article

(extra credit!) Proceedings of the Royal Society B: Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynamics

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