May 24, 2017

How did whales get so big? New study has the answer

We are "living in a time of giants", according to a Stanford University researcher who has been investigating how whales got to be as huge as they now are. Once upon a time, they were much smaller.

In fact, body mass in the biggest whales grew from around 10 tons to 100 tons over just a few million years of evolution. So how did it happen?

According to new research, the ancient climatic and oceanic conditions existed for larger whales to trump smaller ones in the survival of the fittest contest, and those conditions continued to exist in a form that allowed larger whales to get even bigger.

A highly efficient way of eating

Researchers working on a recent study believe that a very long time ago, variations in climate had an impact on the food eaten by some whales, such as krill and small fish.

The conditions caused these sources of food to become more concentrated in certain pockets of the oceans, and bigger whales thrived on that situation.

Baleen whales - a group that includes the enormous blue whale - have eating apparatus of the same name. The baleen filter is composed of keratin (which human fingernails are made from) and looks like a comb's bristles.

Baleen whales gulp in vast amounts of water when eating, then expel it. Food remains behind, caught in the baleen filter. With this very effective method, a lot of food can be consumed in one go so long as there are large pockets of food available in the first place - which was the case under the conditions mentioned.

This efficient technique alone would not have been sufficient for big whales to win out. They also needed enough fuel to make the system work to their advantage. Baleen whales may have had the baleen filter for a very long time, but not the vast supply of food.

Stanford University researcher Jeremy Goldbogen explained that: "Baleen evolved about 20 million years ago, and we didn't see the evolution of gigantism until about very recently, about 3 million to 5 million years ago."

That period of change coincided with the start of the ice ages, and more nutrients began flowing into the oceans from increased runoff.

At the same time, there was increased upwelling, which NOAA defines as occurring when: "Winds blowing across the ocean surface push water away. Water then rises up from beneath the surface to replace the water that was pushed away."

These conditions all contributed to a situation in which there were denser patches of food, which is more amenable to large whales. Smaller whales would have benefited in circumstances where there was lots of swimming around to be done in the search for food.

A unique point in history

Referring to a 2013 study published in the ICES Journal of Marine Science, in order to support his findings, Goldbogen said:

"There are cases where food limitation or food production can basically control body size changes on very short time scales." Therefore, "the inference here is that if you have enough food available and very very efficient animals, that perhaps they can evolve larger and larger body sizes."

He added: "We're totally living in a time of giants. Unlike no other time in Earth's history. We have a unique opportunity to study how the largest animals of all time function in these different ecosystems, and that's a lot of fun."

Naturally, these findings make us wonder if the growth of whales has basically ended, or if it is still continuing.

"Are whales still getting bigger?" Goldbogen asks. "If we fast-forward a few million years into the future if food is not limiting, can they evolve even greater body sizes?"

In a time of instant information, that answer is going to be a long time coming.


Image credit: Wikimedia Commons