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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
>> In all limbed vertebrates, Sonic hedgehog is required for normal limbs to develop beyond the knee and elbow joints. Because ancient whales’ hind limbs remained perfectly formed all the way to the toes even as they became smaller suggests that Sonic hedgehog was still functioning to pattern the limb skeleton.
The new research shows that, near the end of 15 million years, with the hind limbs of ancient whales nonfunctional and all but gone, lack of Sonic hedgehog clearly comes into play. While the animals still may have developed embryonic hind limb buds, as happens in today’s spotted dolphins, they didn’t have the Sonic hedgehog required to grow a complete or even partial limb, although it is active elsewhere in the embryo.
The team also showed why Sonic hedgehog became inactive and all traces of hind limbs vanished at the end of this stage of whale evolution, said Cohn. A gene called Hand2, which normally functions as a switch to turn on Sonic hedgehog, was shown to be inactive in the hind limb buds of dolphins. Without it, limb development grinds to a halt. <<
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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
>> In all limbed vertebrates, Sonic hedgehog is required for normal limbs to develop beyond the knee and elbow joints. Because ancient whales’ hind limbs remained perfectly formed all the way to the toes even as they became smaller suggests that Sonic hedgehog was still functioning to pattern the limb skeleton.
The new research shows that, near the end of 15 million years, with the hind limbs of ancient whales nonfunctional and all but gone, lack of Sonic hedgehog clearly comes into play. While the animals still may have developed embryonic hind limb buds, as happens in today’s spotted dolphins, they didn’t have the Sonic hedgehog required to grow a complete or even partial limb, although it is active elsewhere in the embryo.
The team also showed why Sonic hedgehog became inactive and all traces of hind limbs vanished at the end of this stage of whale evolution, said Cohn. A gene called Hand2, which normally functions as a switch to turn on Sonic hedgehog, was shown to be inactive in the hind limb buds of dolphins. Without it, limb development grinds to a halt. <<
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