Whale evolution has always fascinated me, ever since I learned that their evolutionary path took them from sea to land and then back to the sea. Here’s an animation showing how the land-to-sea-again transition may have occurred.
Scientists have now learned about a new aspect of this transition in the baleen found in the jaws of whales.
If you observe a feeding fin, blue or humpback whale, you are likely to catch a glimpse of the bristles of baleen that fill its gaping jaws. Baleen is unlike any other feeding structure on the planet. Made of keratin, the same material as hair and finger nails, baleen hangs from the roof of a whale’s mouth and is used to filter small fish and crustaceans from large gulps of water. As water rushes into the mouth of a whale, the small creatures easily pass through the comb-like bristles, but once a whale’s mouth is full of water, it flushes the water back out, trapping the tiny creatures in the wall of baleen to be swallowed whole.
Scientists don’t know how or when baleen evolved, but the recent discovery of an ancient whale fossil—roughly 30 to 33 million years old—hidden in the collections of the Smithsonian National Museum of Natural History may hold a critical clue.
Scientists have speculated that baleen may have come to replace teeth and the fossil they studied seems to have had both, making it a transitional fossil.
With such a unique method for feeding, it is only logical to ask why this whale would evolve in such a way. What could be the advantage to losing an important feeding tool like teeth?`
First, teeth are expensive. It takes a lot of energy an d resources to build teeth with strong enamel. Slurping food is much more economical when soft food is readily available. Second, this whale lived at a time in Earth’s history when the environment was rapidly changing. As Antarctica broke away from South America at the end of the Eocene, the ocean’s currents were disrupted. Now, with Antarctica alone, a massive current encircles the continent—a change that had massive implications for both atmospheric and ocean temperatures around the globe. While it remains unclear as to how this might specifically have impacted whales, what is clear is that the change in Earth’s climate was a spark that ignited dramatic evolutionary change.
Fascinating stuff.
@Mano in the OP:
Did the article change since you posted about it? Because it currently reads that Maiabalaena had neither teeth nor baleen.
You did remind me that I had read about transitional whales that had both teeth and baleen, at The Loom.
On the Path Towards Leviathan. Whales mentioned: Janjucetus, Aetiocetus. Also excellent cetacean paleoart by Carl Buell
Mano,
It seems that there were two lines of early mysticete evolution. The one that was ancestral to modern baleen whales evolved: teeth > teeth + baleen > just baleen. The other line never evolved baleen. This Maiabalaena fossil is younger than some of the teeth + baleen genera, and therefore is likely not ancestral and belongs to the extinct lineage that never evolved baleen.
Owl mirror @#1 and Christian Stock @#2,
It looks like I read too quickly and misunderstood the article. Thanks for the corrections!
Actually, this is very confusing. And what Christian Stock says contradicts the original paper, although I originally thought the same thing; that Maiabalaena was an offshoot lineage.
But the claim in the original paper is that all baleen whales derive from whales that had lost teeth, like Maiabalaena. There was never a whale with both teeth and baleen (the authors of this paper say); the actual transition was teeth → toothlessness → baleen.
Tooth Loss Precedes the Origin of Baleen in Whales (open access)
Key sentences from the abstract:
(bolding mine, of course)
They are opposing the claims from the paper from 2008 (Morphological and Molecular Evidence for a Stepwise Evolutionary Transition from Teeth to Baleen in Mysticete Whales (also open access)), which Carl Zimmer wrote about in the article I linked to above. The key paragraph in that article is:
It really bothers me that the Smithsonian article leaves that important point out, to the point where the exact opposite of what the paper was saying can be concluded from it. And the paper itself leads with that point and emphasizes it repeatedly! It’s really bad science writing to not point out that the authors of the work in question are making a new and controversial claim. (And as long as I’m griping, it’s badly spell-checked as well; “rooves” is an incorrect pluralization of “roof”)
There may be challenges to this conclusion, too. Will the authors of the 2008 paper just say “Oh, of course, your logic and reasoning are impeccable. We were wrong!”? Or will they try and defend their own conclusions?
Another open-access paper about the tooth-baleen transition, The Origin of Filter Feeding in Whales, from July of 2017, summarizes the controversy while siding with the teeth+baleen model.
Owlmirror,
Thanks for those articles and the comments. My fascination with whale evolution continues to grow.
https://www.bbc.co.uk/programmes/b00kfqm6