Baleen Whales Are Just the Size they Ought to Be

Humpback whale (Megaptera novaeangliae)

 IN THE HUNTER/GATHERER EQUATION, FILTER-FEEDING BALEEN WHALES came down on the gathering side millions of years ago. 

Gathering – in baleens’ case taking the form of filtering shrimp-like krill and other crustaceans, small fishes and phytoplankton out of the ocean waters with great baleen plates in place of teeth – has made them much more efficient feeders than their toothed cousins.

A study by researchers at Stanford University suggests that the largest whales grew to their bulky sizes from a need to generate sufficient body heat to survive in cold waters. But baleen whales’ ability to take in huge quantities of calories has helped make most of them larger than their toothy counterparts. But they’re not likely to grow even larger because…that would be too big.

A silhouette drawing of a blue whale (Balaenoptera musculus) comparing it to a human. A diver, of course. Image: Kurzon, under the Creative Commons Attribution-Share Alike 3.0 Unported license.


Blue whales – baleens who weigh in at 150 tons and 100 feet or so – are the largest animals on Earth. They can charge through a mass of krill (each weighing in at about 2 oz.) with their mouths open to 80 degrees, inflating like a parachute and taking in enough water to equal their own body mass. With each krillish mouthful, according to a separate study, they can acquire 457,000 calories in crustaceous protein, quite a deal considering the energy they expend.

As carnivores, toothed whales have to hunt down individual prey, expending high energy for a lower caloric return. The sperm whale – the largest toothed whale at about 45 tons and 50 feet in length – is famous for making dives to as deep as 3,000 feet, lasting as long as an hour, to hunt giant squids. And for returning with the sucker marks of squids that don’t go willingly.

A section of baleen from a filtering whale’s mouth. Often compared to Venetian blinds, baleen is primarily composed of keratin, the same substance that makes up fingernails.


Some 90 species of whales roam our planet’s oceans, all members of the suborder Cetacea. The baleen family (Mysticeti) encompasses about 15 species, the toothed whales (Odontoceti) about 73 (including 46 species of much smaller dolphins and porpoises, usually discussed as a separate group).

While a common perception of whales may be of animals with large, square heads – that is, the sperm whale design, thanks to the most famous whale of all, Moby Dick – the big-headed boxy shape is an outlier. Nearly all whales, baleen and toothed, big and little, are pretty much torpedo-shaped, no matter their size.




For a long time, it was thought that sea-going animals ballooned in size because life in a watery environment freed them from the constraints of gravity.

But in their paper published in Proceedings of the Royal Academy B,  the Stanford University scientists suggest that large size reflects the need for bodies that can amass the immense numbers of body cells required to maintain body heat in ocean environments. They add that the volume-to-surface ratio is smaller in animals with massive bulk than in smaller ones, enhancing the heat-conserving factor.

They note that marine mammals in general are far larger than their land-based relatives – not just whales but sea lions, seals and walruses. The largest whales are far bigger than the hippos they diverged from, sea lions larger than bears, for example (they don’t mention the significant of layers of blubber as a factor in heat conservation. And, there are exceptions to the bigger-is- beautiful algorithm. Sea otters are definitely small animals – but with lots of fur).

Bowhead breaching.


The transition of land mammals into animals suited for life in the seas some 50 million years ago and the development of baleen lifestyles some 30 million years ago came about as adaptations designed to maximize access to food.

Separate research by scientists at Smithsonian’s National Museum of Natural History and Stanford has suggested that the gigantic whale species we know today are relatively recent. The emergence of gigantic species came only some 4.5 million years ago, possibly because the beginning of the last great ice age triggered a change from consistent warmth to season cooling, boosting the food supply by enhancing upwelling of nutrients from the depths and runoff of nutrients from land-based glaciers.

The ballooning of sizes developed independently in at least three different baleen lineages – the fins and humpbacks, the blues and seis, and the rights and bowheads.

There are limits. The Stanford researchers suggest that if whales were to keep evolving to ever-larger dimensions, their metabolisms would speed up to the point that taking in enough food would become impossible.


For a comprehensive NOAA guide to whale shapes, sizes and other details, click here. 


PRINCIPAL SOURCES: “Whales,” National Oceanic and Atmospheric Administration; “Dolphins and Porpoises,” NOAA; “Independent evolution of baleen whale gigantism linked to Plio-Pleistocene ocean dynammics,” Graham J. SlaterJeremy A. GoldbogenNicholas D. Pyenson, Proceedings of the Royal Society B; “Sea mammals are huge for a reason,”  Angus Chen, Science Magazine news feed;  “What should I know about baleen whales?” Marine Mammal Laboratory, NOAA Fisheries; “Whales Swallow Half a Million Calories in Single Mouthful,” Wynne Parry, Live Science; “Ancient Gap-Toothed Whale Led to Evolution of Efficient Filter Feeding,” “Whales Only Recently Evolved into Giants,” Jen Viegas,;  “Dolphins & Porpoises,” NOAA; “10 Wonderful Whale Facts,” NOAA; “Why Did the Biggest Whales Get so Big?” Ed Yong, The Atlantic; “The Oral History of Toothless Whales,” Jennifer S. Holland, Hakai Magazine; “Whale Facts,”; “How narwhals use their tusks,” Adam Ravetch, World Wildlife Fund.