Posted on 05/20/2006 6:02:56 PM PDT by Al Simmons
Fetus' Feet Show Fish, Reptile Vestiges By Jennifer Viegas, Discovery News
May 18, 2006 The feet of human embryos taking shape in the womb reveal links to prehistoric fish and reptiles, a new study finds.
Human feet may not look reptilian once babies emerge from the womb, but during development the appendages appear similar to prehistoric fish and reptiles. The finding supports the theory that mammalian feet evolved from ancient mammal-like reptiles that, in turn, evolved from fish.
It also suggests that evolution -- whether that of a species over time or the developmental course of a single organism -- follows distinct patterns.
In this case, the evolution of mammalian feet from fish fins to four-legged reptiles to four-limbed mammals to human feet appears to roughly mirror what happens to a maturing human embryo.
"Undoubtedly there are clear parallels between the mammal-like reptilian foot and the human foot," said Albert Isidro, an anthropologist at the Autonomous University of Barcelona, Spain and lead author of the study, which appeared in the journal The Foot.
Isidro and colleague Teresa Vazquez made the determination after analyzing fossils of a number of mammal-like reptiles that lived from 75 to 360 million years ago. The scientists also studied fossils of osteolepiform fish, which appear to be half fish and half reptilian. These fish lived 400 million years ago and had lungs, nostrils and four fins located where limbs would later be found in four-footed reptiles and mammals.
In 33-day-old human embryos, the scientists observed "the outline of a lower extremity in the form of a fin, similar to that seen in osteolepiform fishes." As the embryo continued to develop, the researchers focused their attention on two foot bones: the calcaneous, or heel bone, and the talus, which sits between the heel and the lower leg.
At 54 days of gestation, these two bones sit next to each other as they did within the reptile herbivore Bauria cynops, which lived around 260 million years ago. This ancient reptile had flat, crushing teeth and mammalian features.
At eight and a half weeks of gestation, the researchers found the two embryonic foot bones resemble those seen in the Diademodon vegetarian dinosaur, which lived around 230 million years ago.
"We can tell that the embryo is half way between the reptiles and the mammals (at this stage)," Isidro told Discovery News.
The two foot bones continue to develop until, at nine weeks, they resemble that of placental mammals as they emerged 80 million years ago.
This development of feet in the human embryo mirrors how the foot evolved over millions of years beginning with fish and ending with early mammals, according to the scientists.
Supporting the fish/foot link was the discovery last month of a new species, Tiktaalik roseae, which lived 375 million years ago. It had fish fins and scales, but also limb parts found in four-legged animals.
"Tiktaalik blurs the boundary between fish and land-living animals both in terms of its anatomy and its way of life," said Neil Shubin, professor and chairman of organismal biology at the University of Chicago and co-author of a related paper in the journal Nature.
H. Richard Lane, director of sedimentary geology and paleobiology at the National Science Foundation, said, "These exciting discoveries are providing fossil Rosetta Stones for a deeper understanding of this evolutionary milestone: fish to land-roaming tetrapods (four limbed animals)."
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LOL! That's fine. No copyright. If you improve on it -- then I can borrow it back. :D
How could you possibly know that - and what on earth would lead you to infer it? It must be your suspicion that any question raised about any purported evidence for the theory of evolution is intended as an attack on the theory itself. I think I know why you feel that way, yet it hardly seems a scientific outlook. In fact, it's every bit as dogmatic as the viewpoint you find so threatening.
BTW, and for what it's worth, I was not lying when I said I have no quarrel with the general theory of evolution. I am not a scientist myself, but I did raise a son who is now quite distinguished as a biologist, so I am not one of your fundamentalist foes. I do not think my son shares the "circle the wagons" outlook you guys exhibit here. Frankly, it's embarrassing.
1. Your bringing the subject up in the first place, as if it were relevant to the discussion. 2. Your failure to put the Haeckel episode in context when you did bring it up. I took high school biology in 1959, and Haeckel was presented in the same terms as he would be now.
I would like for you to present some evidence that Haeckel's "ontology" theory has had any support in mainstream biology in the last hundred years, much less support based on wishful thinking or fraud.
I'm looking back at your posts and thinking you are lying about your position, possibly lying about your son, and definitely lying about your support for evolution.
No one parroting so many creationist buzz words can claim to know anything about evolution.
Ah, I am unmasked! OK, I confess: Only the Cognoscenti really understand the Inner Truth of Holy Evolution. We mortals - creationist fools that we are! - can only gape in awe at their Enlightened Brainpower.
More creationists buzzwords. When you present an actual argument we will be able to judge.
Oooooooooooooooooooh! Aaaaaaaaaaaaaaaaaaaaaaaah!
Fellow ex-creationist here. Almagest is exactly correct in his observations. The end-game of YEC is apologetics, seeking to affirm the truth of Scriptures via science. Nothing wrong with that, but it means that most YECs, if given the choice between keeping a literal belief in Genesis or believing (hypothetically) irrefutable evidence that the Earth is older than 6000 years, will choose the latter. Bless their faith. I wish I had such strong convictions and security about my soul, but I'm not cut out for that...
There are two types of IDers that I have witnessed.
First, is the layman who may accept common descent, but has a vague feeling that "we can't possibly have evolved from rocks".
Second, is the YEC trying to present a more palatable version of young-earth creationism.
Note that both types exclude a serious study of ID on its own merits. ID as a honest science would go beyond irreducible complexity, and attempt to explain some of the nature of the designer: how the designer combined DNA from different species to make new life, and where, and when. Where's the giant labratory? Where did the designer go and why? What evidence is there for the manipulation and tampering of DNA?
All roads point to YEC.
Not that there's anything wrong with that.
Errr.. they will choose the FORMER, not latter. Sorry.
There seems to be a school of ID that is little more than the anthropic principle.
And by "slightly" I mean so slightly as to defy imagination. We are very near "take off" in regard to controlling our own and other genomes. Once that happens, the evidence of a "wild state" will disappear rapidly. I can see folks a thousand years from now debating whether or not there ever were any "wild genomes".
Yup ~ a slightly more advanced civiliation than our own churned it all out in their genome factories.
If the genome were developed by some sort of engineer/scientist, why do some marsupials have egg teeth they never use? Wouldn't it make more sense to not include or to deactivate those genes?
Certainly a competent designer would have done something about the recurrent laryngeal nerve, especially in giraffes.
Can't imagine engineers in a slightly more advanced civilization than our own failing to make mistakes.
Musta been a government-run operation. The private enterprise designers do much better work. But Earth was sort of a job-corps project.
What was the marsupial prototype that needed an egg tooth? A monotreme? As in the ToE?
So why do mammalian jaw bones migrate to the ears? Wouldn't it be easier to leave the jaw alone and just improve the ear?
An engineer would obviously seek to have all the basic scaffolding work for bones done early on. You'll notice ALL the bones are laid out quite early, and then built up as the critter grows. Growth planned for the future takes place at the ends.
It's a process akin to that used to build up an oil painting or build a photo resist.
I'd suggest that the inner ear bones serve as an amplifier for the ear itself, and that function may well have been performed back when they made up 6 bones in the jaw ~
Perhaps you could share at what stage of gestation each of these are and post pictures that compare their relative actual sizes. If each one of these is at a different relative stage of gestation and their sizes vary greatly then posting pictures in which they appear to be superficially similar is kind of silly.
So, what happened to the wombs in the marsupials?
You mean "eutherian mammals" or "placental mammals"; there are three orders in the class mammalia (monotreme, marsupial and placental)
IIRC, there were one or two fossil eutherians found in Australia - do you have a citation?
However, the marsupials appear to have been better adapted and outcompeted the mammals leaving Australia without [euthereian] mammals for tens of millions of years.
So it seems. A similar thing happened in S. America, although there were more eutherians, there were lots of marsupials too.
So, what happened to the wombs in the marsupials?
I don't understand. Judging from the eggshell, egg teeth, and lack of placenta, I'd say they developed from oviviviparous ancestors, who came from monotreme-like ancestors.
Why would you conclude that something happened to their wombs?
Well, why not. We have to get marsupials from somewhere. It doesn't necessarily have to be the case that mammals arise from marsupial stock. After all, the marsupials proved themselves to be the better adapted sort of animals.
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