Dolphin reveals an extra set of ‘legs’

[JohnMK]

Dolphin reveals an extra set of 'legs' - Science - MSNBC.com

TOKYO - Japanese researchers said Sunday that a bottlenose dolphin captured last month has an extra set of fins that could be the remains of hind legs, a discovery that may provide further evidence that ocean-dwelling mammals once lived on land. Fishermen captured the four-finned dolphin alive off the coast of Wakayama prefecture in western Japan on Oct. 28, and alerted the nearby Taiji Whaling Museum, according to museum director Katsuki Hayashi. Fossil remains show dolphins and whales were four-footed land animals about 50 million years ago and share the same common ancestor as hippos and deer. Scientists believe they later transitioned to an aquatic lifestyle and their hind limbs disappeared.

Intriguing. Could this dolphin or its mother have been subject to some kind of environmental toxin which exposed a normally obscure and antiquated genotype, or was this just random fluke? Either way this is noteworthy.

[Hostile55]

Yeah I like it when things like this pop up too. What I really found intriguing was the fact that in the womb, at a certain stage of development, the human foetus has gills and a tail.

[gallo]

Quote by: Hostile55 Yeah I like it when things like this pop up too. What I really found intriguing was the fact that in the womb, at a certain stage of development, the human foetus has gills and a tail.

A tail, yes. Gills, never. The human foetus, just like all vertebrates develop structures that are called "gill slits." They are not gills, and not slits. In fish, the gill arches do develop from these structures but in humans and other verts other structures of the neck and ears develop from them. Maybe they should be referred to as the pharyngeal pouches.

Also, all whales and dolphins begin to develop legs in their early embryonic development. Some species of whale retain bones that are remnants of the pelvis and the rear legs (femur), and occasionally whales have been found with the remnants of rear legs, much like this dolphin. Fossil whales such as Dorudon, Basilosaurus, Gaviocetus, Takracetus and Rodhocetus, while fully aquatic, still had hind legs, none of which functioned as legs. Older whales actually walked on land, like Dalanistes and Ambulocetus.

These extra fins serve no survival purpose and may, in fact, be detrimental. They don't seem to offer an advantage in maneuverability, and do create more drag. Thus we have a slower dolphin. This is not an advantage in the presence of predators. Statistically, dolphins without hind legs have a slight survival advantage over those who do have them, which means that dolphins without hind legs tend to produce more offspring than those who do. Thus, most dolphins don't have hind legs. It's called natural selection.

[kubedawg]

Could it be a sign of evolution from dolphin to human!?

[Fonceai]

Actually it's more a sign of the opposite.

If all mammals start with legs of some sort, and then develop otherwise in dolphins and whales, it suggests that, as stated earlier, that there was some form of land creature that evolved for the ocean.

[gallo]

Quote by: kubedawg Could it be a sign of evolution from dolphin to human!?

No. Humans don't have dolphin ancestors. What a silly idea. Besides, individuals do not evolve, populations do.

[kubedawg]

Well I think it's a solid theory compared to the whole "mokey" theory. Dolphins are so smart compared to poo throwing monkeys..

[Fonceai]

Oh come on now...

If it were socially acceptable for you to take a hot steaming dump into your hand and wing it at some asshole who offends you, wouldn't you do it?

---

I think it just proves that dolphins are derived from some sort of land-dwelling mammal. Sucks to be them to not have developed the bodies to build tools.

[gallo]

Quote by: kubedawg Well I think it's a solid theory compared to the whole "mokey" theory. Dolphins are so smart compared to poo throwing monkeys..

Well, it's solid something, but it isn't a theory. Why imagine anything about an aquatic mammal when there are perfectly good animals that already have 4 limbs out in the sty to imagine as your ancestors?

By the way, what "mokey" theory are you talking about? What's a "mokey"? What does a "mokey" have to do with monkeys? Why do you imagine that poo throwing is meaningful to your ancestors? Do "mokeys" throw poo too? In your opinion, is poo throwing necessary for a solid theory?

Are dolphins smarter than "mokeys"? Are dolphins smarter thatn monkeys? How do you know?

[kubedawg]

Quote by: Fonceai Oh come on now... If it were socially acceptable for you to take a hot steaming dump into your hand and wing it at some asshole who offends you, wouldn't you do it? --- I think it just proves that dolphins are derived from some sort of land-dwelling mammal. Sucks to be them to not have developed the bodies to build tools.

Nah, I don't do things based upon them being socially acceptable. It'd have to be something bad that they did to piss me off, not because my friends or others thought it was a good idea. You really don't think in the early stages of human life we didn't have fins and/or gills?

[Fonceai]

Current embryonic development? No.

Earlier forms of the mammal that would someday develop into humans? Maybe.

The ability of a fetus to breathe liquid is similar to gills, but only because that fluid is oxygen-enriched.

The appearance of arms and legs being fins is closer evidence, as it demonstrates that the appendages develop into hands/arms and feet/legs later but had their basis in fins.

Really though, because of the many many evolutionary leaps required to go from fish to land-fish to land creature to mammal that while reasonable to say that everything came from fish, dolphins and whales don't represent a lower step in the process.

They represent a later step... the development of land mammals to water.

Basically acquiring the advantages of land life and bringing them back to the sea.

[gallo]

Quote by: Fonceai Quote by: kubedawg You really don't think in the early stages of human life we didn't have fins and/or gills? Current embryonic development? No.

Aside from the grammatical confusion of the question caused by the double negative that injects considerable uncertainty of meaning, Fonceai is correct. If by "early stages of human life" kubedawg is referring to human embryos, then no we never had fins and/or gills. In fact, dolphins don't ever have gills either, and they have fins only in the broadest sense of the word.

Quote by: Fonceai Earlier forms of the mammal that would someday develop into humans? Maybe.

Nope. No mammal, embryonic or otherwise ever has fins or gills. As I explained to Hostile55 in post #3, "gill slits" and never become gills in mammals. They are folds caused by pharyngeal pouches that are characteristic of all embryonic chordates.

Quote by: Fonceai The ability of a fetus to breathe liquid is similar to gills, but only because that fluid is oxygen-enriched.

Nope. a foetus doesn't actually breathe liquid. The necessary oxygen for the foetus comes through the placenta from mother. CO2 is eliminated the same way. Early on, before the development of the placenta, the embryo is small enough that it can absorb oxygen and eliminate waste directly into the environment of the womb. But it can't actually be called "breathing."

Quote by: Fonceai The appearance of arms and legs being fins is closer evidence, as it demonstrates that the appendages develop into hands/arms and feet/legs later but had their basis in fins.

Except that as I recall from my embryology class, human embryos never do have fins. They have limb buds that are homologous to the fins of fish at about the same stage in development, but they don't even resemble fins. One must always remember that ontogeny does not recapitulate phylogeny.

Quote by: Fonceai Really though, because of the many many evolutionary leaps required to go from fish to land-fish to land creature to mammal that while reasonable to say that everything came from fish, dolphins and whales don't represent a lower step in the process. They represent a later step... the development of land mammals to water.

Exactly correct, as I also explained in post #3. A very interesting book on the topic is Zimmer, Carl. At The Water's Edge: Fish With Fingers, Whales With Legs and How Life Came Ashore but Then Went Back to Sea. 1998. Simon & Schuster. New York. 290 pages.

Even though the book isn't that old, there is one error in scientific thought that is apparent. Zimmer expresses earlier theory on the origin of whales as descended from mesonychids. Molecular biology indicates that that is not the case. They are more closely related to the artiodactyls (even-toed ungulates). Nevertheless, the book is very interesting.

Quote by: Fonceai Basically acquiring the advantages of land life and bringing them back to the sea.

Right, as long as you keep in mind that the first terrestrial vertebrates appeared about 400 million years ago, about 100 million years after land plants and about 350 million years before whales began to adapt to water.

[Fonceai]

@gallo

Good stuff. Thanks for clearing up the finer points. I was aware of the technical differences but I was merely citing the similarities that could be "misleading".

The only challenge I have to that is the breathing amniotic fluid. It serves as both air, food, and toilet for the baby. I watched my daughter "inhale" fluid and it filled her lungs and belly. Then I watched it slowly leave her mouth as her lungs deflated, while it also left her groin as her stomach deflated.

[gallo]

Quote by: Fonceai The only challenge I have to that is the breathing amniotic fluid. It serves as both air, food, and toilet for the baby. I watched my daughter "inhale" fluid and it filled her lungs and belly. Then I watched it slowly leave her mouth as her lungs deflated, while it also left her groin as her stomach deflated.

Depends on what you mean by breathing. A foetus does "practice" breathing by taking in and expelling amniotic fluid, and of course, waste products are expelled into the amniotic fluid, but it isn't "breathing" in the primary sense of the word. Oxygen comes from the mother through the placenta and CO2 goes back the same way. Here's how that works. The mother breathes air into the lungs where O2 passes through the into the blood (attaches to the hemoglobin). From there carried to the heart and then pumped out to the body. Part of that is the small blood vessels in the wall of the uterus. From there the blood passes through into the small vessels of the foetus in the placenta which are in close association with the uterine wall. From there blood is circulated to the foetus. The lungs do not function in this so a foetus does not "breathe." This should be made clear from the existance of the ductus arteriosis, and the foramen ovale, that allow most blood to bypass pulmonary circulation. (A third, the ductus venosus, causes most blood to bypass the liver.) It is the first breathing of a newborn infant that causes a cascade of physiological changes that cause the ductus arteriosis to immediately reduce and quite soon stop functioning. The foramen ovale is the infamous "hole in the heart" that requires surgery soon after birth when it fails to close as it should.

All in all, it depends on what you are talking about when you say "breathe," breathing motions or air exchange in order to get O2.

[Fonceai]

Ahhh... spiffy.

Then since that was the only questionable thing for me, I can now say conclusively there is no fish-like traits in a developing human fetus; only things that appear similar.

[gallo]

Quote by: Fonceai Ahhh... spiffy. Then since that was the only questionable thing for me, I can now say conclusively there is no fish-like traits in a developing human fetus; only things that appear similar.

Ah! Good.

But if you want to say that you saw your daughter "breathing" in the womb, and by that you mean exercising developing chest muscles and the diaphragm, then feel free. That's what they are doing. A foetus has also been observed to cry, or so it appears, which is also good exercise for muscles.

[Fonceai]

To my layman eyes, I saw her diaphragm expand, lungs fill, and lungs empty. It sure looked like "breathing".

Other than that, it doesn't make sense that mammalian development would start with such characteristically aquatic... errr... characteristics. Heh heh.

[Flea_Bit_Monkey]

I saw a cloud that looked like an elephant.

Clearly elephants evolved from clouds.

[Jack]

Clearly elephants evolved from clouds.

Cute idea. It actually makes as much sense as the idea that dolphins and elephants were created just as they are today by an invisable superman about 6000 years ago.

[kubedawg]

ZOMG THAT'S AN AWESOME THEORY!

But, what I meant was not the embyonic development of a human, but the evolution from bacteria, to dolphin, to human.