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Evolution of whales

Evolution of whales

A similar cladogram

 

Why would whales have bones similar to that of a pig or dog?

ankle bones of dog Pakicetus (whale) pig deer

Where do cetaceans lie on the family tree of mammals?

 

Jerry Coyne writes:

The paper I want to write about by Thomas Deméré and his colleagues…one of the best papers I’ve seen about a transitional form. The transition is between modern baleen whales and their toothed ancestors. Baleen whales are in the suborder Mysticeti of cetaceans; all of the species are toothless. (The other order, the toothed whales, is Odontoceti.) Instead of teeth, mysticetes have baleen, a basketlike substance in the upper jaw which is used in filter feeding. Baleen is not bone: it’s made from keratin that’s secreted from the whale’s palate. The secreted substance is abraded by the whale’s tongue, producing a filamentous, fringe-like structure :

The baleen basket is used in feeding, and acts like a sieve.  The whale gapes its mouth, gulping in a huge volume of water containing small fish, zooplankton, and invertebrates. It then closes its jaws a bit and, using its tongue, squeezes out the water, trapping the prey against the baleen. …

Baleen had a lot of uses during the days of whaling; one was to make the supporting struts in “whalebone” corsets.  It doesn’t fossilize well, so the ancestry of baleen whales is deduced from other skeletal features and from DNA. From these we know that the earliest baleen whales actually had teeth. The paper by Deméré is about this transition.

Before I mention their results, I want to show one photo from their paper that supports this evolutionary scenario.  Baleen whales, though toothless, develop tooth buds when they’re embryos.  In toothed whales these buds go on to become the adult teeth, but in baleen whales they degrade and disappear.   I mention this in WEIT as evidence for evolution…

https://whyevolutionistrue.wordpress.com/2010/07/22/baleen-whales-a-lovely-transitional-form/

Deméré, T. A., M. R. McGowen, A. Berta, and J. Gatesy. 2008. Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales. Systematic Biology 57:15-37.

Deméré, T. A., M. R. McGowen, A. Berta, and J. Gatesy. 2008. Morphological and molecular evidence for a stepwise evolutionary transition from teeth to baleen in mysticete whales. Systematic Biology 57:15-37.

Also see

http://evolution.berkeley.edu/evolibrary/article/evograms_03

 

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