Humpback whale femur, tibia, tarsis, and metatarsal. Found here.
Posted on 05/23/2006 4:08:38 AM PDT by PatrickHenry
When ancient whales finally parted company with the last remnants of their legs about 35 million years ago, a relatively sudden genetic event may have crowned an eons-long shrinking process.
An international group of scientists led by Hans Thewissen, Ph.D., a professor of anatomy at Northeastern Ohio Universities College of Medicine, has used developmental data from contemporary spotted dolphins and fossils of ancient whales to try to pinpoint the genetic changes that could have caused whales, dolphins and porpoises to lose their hind limbs.
More than 50 million years ago the ancestors of whales and dolphins were four-footed land animals, not unlike large dogs. They became the sleek swimmers we recognize today during the next 15 million years, losing their hind limbs in a dramatic example of evolutionary change.
"We can see from fossils that whales clearly lived on land - they actually share a common ancestor with hippos, camels and deer," said team member Martin Cohn, Ph.D., a developmental biologist and associate professor with the UF departments of zoology and anatomy and cell biology and a member of the UF Genetics Institute. "Their transition to an aquatic lifestyle occurred long before they eliminated their hind limbs. During the transition, their limbs became smaller, but they kept the same number and arrangement of hind limb bones as their terrestrial ancestors."
In findings to be published this week in the Proceedings of the National Academy of Sciences, scientists say the gradual shrinkage of the whales' hind limbs over 15 million years was the result of slowly accumulated genetic changes that influenced the size of the limbs and that these changes happened sometime late in development, during the fetal period.
However, the actual loss of the hind limb occurred much further along in the evolutionary process, when a drastic change occurred to inactivate a gene essential for limb development. This gene - called Sonic hedgehog - functions during the first quarter of gestation in the embryonic period of the animals' development, before the fetal period.
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.
"By integrating data from fossils with developmental data from embryonic dolphins, we were able to trace these genetic changes to the point in time when they happened," Thewissen said.
"Studies on swimming in mammals show that a sleek body is necessary for efficient swimming, because projecting organs such as rudimentary hind limbs cause a lot of drag, and slow a swimmer down," said Thewissen, who spends about a month every year in Pakistan and India collecting fossils that document the land-to-water transition of whales.
Researchers say the findings tend to support traditional evolutionary theory, a la Charles Darwin, that says minor changes over vast expanses of time add up to big changes. And while Sonic hedgehog's role in the evolution of hind limbs in ancient whales is becoming apparent, it is still not fully defined.
"It's clear when ancient whales lost all vestiges of the limb it was probably triggered by loss of Sonic hedgehog," said Clifford Tabin, Ph.D., a professor of genetics at Harvard Medical School who was not involved in the research. "But it's hard to say for certain because you're looking at events long after they occurred. As they suggest, there could have been a continual decrease in Sonic as the limbs reduced until the modern version of the animal arrived."
The study itself, combining fossil and developmental data, is notable, Tabin said.
"Whales went through this remarkable transformation to become more like the ancestral fish," Tabin said. "Convergence of evolutionary studies and developmental genetics give us another piece in this growing tapestry of how genetic changes lead to morphological change. It is a remarkable process that was achieved simply and led to profound consequences in how whales were able to survive. Only now in the last five years are we developing this understanding of how the world of evolution is controlled genetically."
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In addition to UF and Northeastern Ohio Universities College of Medicine, scientists from the Natural History Museum of Los Angeles County and the Indian Institute of Technology were involved in the research. Financial support was provided by the National Science Foundation, the National Institutes of Health and the Indian Department of Science and Technology, New Delhi.
I posted that I admitted my error. What is it you would rather have me do?
I'm human. I use sarcasm at times when it offends, but doesn't entertain. I appologize.
I have done a cursory overview of my most recent posts of today and yesterday. I say have a nice day or night. I respond kindly to people I wasn't even corresponding with jump on a post and claim strange things. These things you seem to have failed to notice.
I truely don't understand CarolinaGuitarman. He seems hung up an a word. I wasn't even debating him. The correction to my (admittedly bad) sumation of what evolution claims didn't change what I was trying to get across to someone else.
I think you fail to see the vindictiveness on your own side. Where do CarolinaGman or others ever wish me well?
I'll admit to jumping in Evo threads that I disagree with, and if that is trolling then so be it, but I don't do it with the intend of belittling someone. I do it to make a stand for what I believe. I thought that's what Freerepublic was for. If my beliefs can't stand up to the criticism they recieve, then I should leave. So far that hasn't happened.
When people like CarolinaGuitarman, whom I didn't post anything to, jump into my posts, they invaribly do it with superiorist sarcasm. I sometimes respond in kind. Maybe not Christ-like, but I figured they could handle their own medicine.
I may, in the future, restrain my sarcasm, but I will continue to post my beliefs. If you or the Mods think it is inappropriate, then report me or remove me. Until then......Be seeing ya.
This is total b.s.; Whales never had legs. This is one of the big lies of science.
"It's not my fault. Those mean old evo's talk to me when I try to pontificate. It's not fair."
Excuses, excuses. Exactly as we are taught to do in scripture -- right?
"This is total b.s.; Whales never had legs. This is one of the big lies of science."
No, Senor Galileo. I will NOT look through that telescope. What you saw is NOT TRUE, no matter what. There's no point in looking, because it's not there. [Putting hands over ears and closing eyes tight -- and singing 'LALALALALALALALA -- I can't HEEEEAAAARRRR you!"
"Thank you. Now I can sleep tonight."
Glad to be of service.
"I hope that sarcasm wasn't too cruel. If it was I'll extend this thread with another apology."
No doubt.
"Not excuses friend, defense of what I believe."
So let me get this right. Castigating the other poster for having evolution as her/his "god" is a defense of what you believe.
You are delusional. Once again, I have wasted my efforts in appealing to someone's conscience.
Hey, Scubi -- we have had a lot of back and forth, and in all the scuffle, I noticed that you never did answer my question. You had claimed that speciation had never occurred -- and I responded with a question. I would appreciate an honest answer, in the Christian spirit that you claimed to aspire to, and without the sarcasm that you apologized for.
Please get back to me on this. I know you are concerned with truth, and that if you find that you have said something untruthful, even inadvertantly, you would want to correct it -- right? This question goes directly to the heart of your claim about the lack of speciation, and it's a very simple question. Here it is again:
Why can't domestic wheat interbreed with emmer grass?
Humpback whale femur, tibia, tarsis, and metatarsal. Found here.
<< thank you for not answering my questions,but here is a simple one, what color skin did Adam and Eve have? >>
Hey, Scubie -- speaking of not answering questions -- I have one for you that I have asked several times now, and I still don't see any answers. Here it is again:
If speciation does not occur, why can't domestic wheat interbreed with emmer grass?
If you are continually inaccurate in merely quoting people on this thread, why should we believe that anything else you say is accurate?
He's partially correct. Whales never did have legs nor does science claim so. Whales's ancestors had legs and hippos share these ancestors.
Here's the problem. We have long had a series of whales called Archaeocetes with primitive features unknown or atavistic on modern whales. Legs and pelvises visibly shrinking over time. Nostrils visibly rising on the head over time to become the modern blowhole. But these were all still fully marine animals.
The 80s and 90s have further fleshed out the picture. We have a fully terrestrial land artiodactyl, Pakicetus. We have an obvious but later near-relative (similar head) Ambulocetus, about as aquatic as a crocodile. We have a later near-relative Rhodocetus about as aquatic as a pinniped (seal, walrus). Still has the head similarities and still has an artiodactyl ankle bone, the astralagus. The series has fleshed out in other places as well.
And what your link refers to only elliptically in the most negative light it can manufacture is that whales are molecularly speaking even-toed ungulates. All it can do is find someone somewhere expressing incredulity at how unrelated traditional taxonomy has made cows and whales, given the molecular relatedness.
We have the clear forensic trail in the fossil record and molecular biology. All creationists can do is squirm and quote-mine. This is weaker than weak. Given clear and positive evidence that a thing has happened, evidence which makes no sense at all if the thing didn't happen, it DOESN'T MATTER if we don't know every detail down to the molecule of how it happened. It does no good to invent silly excuses why it was supposedly impossible.
The exact parallel happens in discussions of dinosaurs becoming birds. Someone will post something along the lines of "A theropod claw can't become a wing because the in-between thing is not a wing and not a claw and no good as anything."
To which I post a picture.
That is the forelimb of what creationists, shrieking in denial, call "A bird! Just a bird! Not a transitional!"
And to deal with another point of yours, said pictures never convinces the nutcase who made the point being answered of anything. Never. After all, he's nuts.
But I can hear the lurkers belly-laughing.
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