Evidence for cetacean evolution

[Bret]

This is a comment I've saved on a Word document so I don't have to keep typing it out over and over. I look at three examples of evidence that cetaceans evolved from terrestrial mammals without using fossil evidence.
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If whales evolved from terrestrial mammals we would expect to find certain things in addition to the characteristics that undeniably make them mammals.

From physiology we see that unlike fish and marine reptiles (see the ichthyosaur body plan), which move side to side, whales should move up and down just like their terrestrial counterparts do. Indeed, that is what we observe. A potential falsification would be if they undulated side to side and their flukes were shaped and positioned like those of Ichthyosaurs.

Based on the fact that we've observed atavistic legs on whales, we would expect from genetics and embryology to see that they retain anatomical or molecular vestiges for hind leg development. We observe both.

Embryonic dolphins develop limb buds that are absorbed back into the body as the fetus grows. (see photo at bottom of page)
http://palaeo.gly.bris.ac.uk/palaeof...es/biology.htm

Cetaceans also have the gene package for limb development. In legged vertebrates, Sonic Hedgehog and Hand2 work together to develop them, but in cetaceans that gene package is non-functioning so the limb buds never develop unless there is a problem and atavistic hand limbs actually grow.
http://www.pnas.org/content/103/22/8414.full

Press release here:
http://news.ufl.edu/archive/2006/05/...he-oceans.html

[shunyadragon]

This is a comment I've saved on a Word document so I don't have to keep typing it out over and over. I look at three examples of evidence that cetaceans evolved from terrestrial mammals without using fossil evidence.
------------------------------------
If whales evolved from terrestrial mammals we would expect to find certain things in addition to the characteristics that undeniably make them mammals.

From physiology we see that unlike fish and marine reptiles (see the ichthyosaur body plan), which move side to side, whales should move up and down just like their terrestrial counterparts do. Indeed, that is what we observe. A potential falsification would be if they undulated side to side and their flukes were shaped and positioned like those of Ichthyosaurs.

Based on the fact that we've observed atavistic legs on whales, we would expect from genetics and embryology to see that they retain anatomical or molecular vestiges for hind leg development. We observe both.

Embryonic dolphins develop limb buds that are absorbed back into the body as the fetus grows. (see photo at bottom of page)
http://palaeo.gly.bris.ac.uk/palaeof...es/biology.htm

Cetaceans also have the gene package for limb development. In legged vertebrates, Sonic Hedgehog and Hand2 work together to develop them, but in cetaceans that gene package is non-functioning so the limb buds never develop unless there is a problem and atavistic hand limbs actually grow.
http://www.pnas.org/content/103/22/8414.full

Press release here:
http://news.ufl.edu/archive/2006/05/...he-oceans.html

Great post welcome to Tweb!!

[Bret]

Great post welcome to Tweb!!

Thank you. And I was USincognito on old TWeb.

[shunyadragon]

Thank you. And I was USincognito on old TWeb.

Well . . . welcome back to the reincarnation of Tweb (tWeb?),

[shunyadragon]

I would like to see more genetic research establishing these relationships.

[Bret]

There's a ton of related papers that pop up when you search for whale evolution. Sticking with anatomical changes, they have found changes to the hoxd12 and hoxd13 are responsible for cetacean flippers.
http://www.ncbi.nlm.nih.gov/pubmed/19074008

To test whether the evolution of the cetacean forelimb is associated with positive selection or relaxation of Hoxd12 and Hoxd13, we sequenced these genes in a wide range of mammals. In Hoxd12, we found evidence of Darwinian selection associated with both episodes of cetacean forelimb reorganization. In Hoxd13, we found a novel expansion of a polyalanine tract in cetaceans compared with other mammals (17/18 residues vs. 14/15 residues, respectively), lengthening of which has previously been shown to be linked to synpolydactyly in humans and mice. Both genes also show much greater sequence variation among cetaceans than across other mammalian lineages. Our results strongly implicate 5'HoxD genes in the modulation of digit number, web forming, and the high morphological diversity of the cetacean manus.