Evolution: whale teeth and baleens (Evolution)

by David Turell , Friday, November 30, 2018, 15:06 (2183 days ago) @ David Turell

David: The way some whales feed they don't need teeth:

https://phys.org/news/2018-11-whales-lost-teeth-evolving-hair-like.html

For some reason the excerpts didn't publish. From a different article:

https://www.newscientist.com/article/2186912-prehistoric-whales-used-to-simply-suck-the...

Whales were once all toothed predators. Around 36 million years ago, a group of them evolved to lose their teeth. We don’t know what drove that evolutionary trend, but it ultimately gave rise to today’s filter-feeding whales, including blue whales and humpback whales, that use baleen bristles in their mouths to remove tiny prey from the water.

Scientists haven’t been able to precisely reconstruct what happened during whales’ transition from teeth-bearing to filter-feeding – but they had assumed that the filter-feeding system emerged before the whales lost all their teeth.

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Using CT scans, the team found the extinct whale (Maiabalae nanesbittae) had no alveoli – teeth sockets. It also had a different mouth structure than baleen-bearing whales, meaning it had no ability to filter-feed either.

“[The whale] represents a surprising intermediate stage between modern filter-feeding whales and their toothed ancestors,” Peredo says. “Our study makes it very unlikely that teeth and baleen existed at the same time in the same animals.”

Peredo suggests baleen might have appeared 23 million years ago, about 10 million years after whales lost their teeth.

But how did M. nanesbittae capture prey? Peredo says this whale was probably a suction-feeder like modern salmon and trout. The whale has an enlarged bone in the back of its mouth, resembling those observed in suction-feeding fish. Such bones help the mouth muscles generate a strong sucking force.

The transformation from a biter to a suction-feeder then into a filter-feeder also tells us about when whale diets changed. Sucking and biting are techniques that work best when the animal aims to take one target at a time, whereas filter-feeding targets bulk quantity of tiny organisms.

“There’s a good chance that [filter-feeding] is more energetically efficient,” Peredo says. “It seems to be a successful body plan for marine mammals.”

Comment: When a mammal enters a new environment to live the changes have to be very complex and enormous. Just hopping into the water doesn't work. Losing teeth and gaining a filter system isn't done stepwise. It has to be designed.