Innovation and Speciation:baleen whale feeding (Evolution)

by David Turell @, Wednesday, June 07, 2017, 18:49 (288 days ago) @ David Turell

About 30 million years ago some whale forms changed from teeth to baleen feeding. They are like large vertical venetian blinds hanging in whale mouths to filter tiny aquatic prey:

In a recent paper published in PLOS One,... detail for the first time how baleen whales use crossflow filtration to separate prey from water without ever coming into contact with the baleen. Baleen are comb-like keratin plates that have replaced the teeth of the whale's ancestors about 30 million years ago and play the role of a filtration surface in their mouths. The researchers looked at how this type of feeding affects a whale's drag as it moves through the water and how this form of filtration is enhanced by a large body size.


We study the physics of the various feeding mechanisms used by whales such as the humpback, blue and right whales. One practical aspect of this research is to know how much food they need. For the largest species, the food is krill and copepods.


"Blue whales, for example, feed on millions of krill that gather in big patches, in many cases patches that are larger than the whales themselves. This allows whales to grow to enormous sizes. These whales are the largest animals to have ever lived on Earth -- they are larger than most dinosaurs. They engulf water and prey, and then filter what they don't need out through the baleen plates.

"There's still a lot we don't understand about filtration by baleen, especially with regards to the detailed physics involved. Blue whales lunge toward the prey patch and open their mouth to enormous gapes to catch as many prey as possible. In the process they engulf an enormous amount of water which needs to be filtered out instants after mouth closure. Blue whales engulf the equivalent of their own mass, which for a 90 foot-long whale translates into a hundred tons of water. This is a lot of water to purge out of the mouth. It's done after prey capture, with the whale's belly muscle tightening to force the water through the baleen, past the lips and out of the mouth. This is a complicated process, most of which is out of view. This leaves scientists with very few clues on the workings of the filtration process that takes place within."

In their current paper, Potvin and Werth studied another type of baleen whale, the right whale, which offer a simpler version of filtration by baleen. Right whales have a baleen system that is similar to that of blue whales, although with longer baleen plates. But unlike their distant cousins the blue whales, right whales do not lunge and catch their prey like a raptor. Instead, they skim the water with their mouths open to collect their food at a much slower pace, effectively eating like a grazer. This process also is more visible since it is performed with the mouth partially opened. And, because of this skimming motion, the flow of water moving though the baleen system is simpler to simulate mathematically than the flows taking place inside a blue whale's closed mouth.

Right whales feed on small prey called copepods which are about the size of a grain of rice.
"Copepods also hang out in big patches," Potvin said. "Whales open their mouths while swimming through the patch, effectively skimming through it in a manner similar to a collector's net capturing butterflies. Again the baleen act like a filtration surface but the copepods are smaller than the space between baleens and so the filtration process must be different from, for example, draining pasta using a strainer.

"Instead, crossflow filtration is used, with most of the water passing through the baleen and exiting out of the mouth, but with the prey heading straight to the back side of the mouth where it is swallowed, all the while without ever coming into contact with the baleen.The copepods are mostly a slurry of food by the time they get to the whale's esophagus.

Comment: this article is presented to show another of the complexities the evolution of whales faced in becoming aquatic. And remember whales have to handle the metabolism of salt water, too much of which will kill a mammal. My question is still why did God bother?

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