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NYCOM Professor Matthew Mihlbachler examines horse teeth.  (Source: Matthew Mihlbachler)

Prehistoric horses shifted from eating berries and fruit (like the pictured "Dawn Horse"), to leafy plants, then finally to grass as climate and vegetation changed.  (Source: Encyclopedia Britainnica)

Horses evolved in North America, but ironically all North American species perished at the end of the last ice age. The horses today are modern Eurasian descendants of ancient North American breeds.  (Source: University of Texas)

Modern horses have long teeth and complex cusps, well adapted for chewing high-silica grass.  (Source: Google Images)
Dietary changes take as much as a million years to broadly select a particular population, say researchers

Evolution says that the genetic material of the fittest species will typically survive and displace that of less fit species.  But there's much debate over finer details, such as how fast this process happens.  

Paleodental researchers at the New York College of Osteopathic Medicine have completed an important new study [press release] that examines how fast the process of evolution operates in response to changes in available diet.  The study looks at a relatively vast array of fossilized horse teeth and fossilized plant materials that date back as far as 55 million years ago.  

Their conclusion is that the old adage "you are what you eat" holds true -- if you give it about a million years.

NYCOM anatomy professor Matthew Mihlbachler [profile] said the key to the exciting study was in developing an effective method to tell what the horses were eating.  Past studies looked at the teeth on a microscopic scale or performed chemical tests to try to extract clues on the creatures' diet.  Such methods were laboriously slow.  

But Professor Mihlbachler used a new approach called mesowear.  This approach examines the shape of the tooth, particularly the sharpness of the cusps of molars.  The method is remarkably accurate as tooth shape is directly targeted to a specific animal's diet.

The result was a very comprehensive work.  Describes Professor Mihlbachler in an LiveScience, "We looked at wear patterns on horse teeth using mesowear through the entire history, from 55 million years ago in North America to the extinction at the end of the last ice age."

The horses of 55 million years ago would hardly be recognizable by today's standards.  No bigger than a modern fox, these petite creatures roamed warm, moist forests of North America munching on fruits and berries.  The creatures had four toes and their teeth were rounded to properly deal with their soft food.

Around 33 million years ago, the climate began to change and leafy shrubs suitable for the cooler weather displaced the fruity plants.  The process of evolution by natural selection transformed the horses into slightly larger leaf eaters.  The horses’ teeth became sharper in order deal with the new diet.

Describes Mr. Mihlbachler, "The signal we are getting in the change in horses' diet is very consistent with what we understand about how the climate was changing."

Horses underwent a final evolutionary metamorphosis approximately 18 million years ago as grasslands displaced the cool forests.  Grasses have high silica content, so horses had to develop longer teeth with more complex surfaces to deal with the new diet.  While leaf-eaters (with sharp teeth) persisted for several million years, they were eventually displaced entirely by the grass eaters.  In the mean time the grass eating horses' teeth continue to get longer with passing generations.

By 4 or 5 million years ago, the horses were completely adapted to grass lands.  And it paid off.  Horses expanded across most of North America and expanded across the Eurasian land mass.  There, early humans would encounter them and domesticate them, an encounter that would play a key role in human society.

Before that would happen in full, the pioneer North American breeds would die off, due to the last Ice Age abruptly ending, around 10,000 years ago.  But North America would yet again see horses, when the domesticated Eurasian descendants were reintroduced into the "New World".

The most intriguing thing about the study was not only that the dental record closely followed the change in foliage.  The more interesting thing was that it lagged slightly behind the changes, with the horses taking up to a million years to fully adjust to foliage changes.

This offers interesting evidence into the timescales of major evolutionary adaptation.  And it is relatively consistent with past evolutionary theory.  States Professor Mihlbachler, "The changes in the teeth are just slightly behind the environment and dietary trends, which is very consistent with the hypothesis of adaptation. Certainly, there were leaves and trees throughout all that time period, from 55 million years ago to the extinction. What we don’t know is why horses left those niches."

No scientist would claim that evolution happens the same way every time.  Thus it is important to practice caution when applying these time frames to other species or adaptive events.  But they do offer excellent evidence in support of key evolutionary hypotheses.  

Thomas Scandalis, dean of NYCOM concludes, "You are what you eat,’ we hear this all the time, but now we know it is true."

The paper on the work was published [abstract] in one of academia's most prestigious journals, Science.

If you're hungry for more evolutionary anatomical research, dig into NYCOM's February study [press release] [abstract] which examined a "bizarre" "pudgy" crocodile that lived in Madagascar, right before the mass extinction of the dinosaurs.  If you expected a vicious dinocroc like you might spot in a Sci-Fi channel movie special, you will be disappointed -- NYCOM Professor Robert Hill [profile] says the beast was a "gentle, vegetarian crocodile."



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RE: Question
By PaterPelligrino on 3/13/2011 11:07:07 AM , Rating: 2
The Oregon State University study you cite is interesting. I don't pretend to be an expert in the field; no doubt much is yet to be learned of the precise path by which birds evolved from earlier species. Nor do I know what the critical response was to that study - there must have been some kind of rebuttal. I do note that there are other studies referenced on that same page that support the dinosaur thesis. In any case, I have no emotion invested in the outcome of the controversy one way or the other; whether birds evolved from dinosaurs or both evolved from a common ancestor, it's all the same to me. However, the OSU study you link to has this to say:

quote:
"This discovery probably means that birds evolved on a parallel path alongside dinosaurs, starting that process before most dinosaur species even existed."

"The newest findings, the researchers said, are more consistent with birds having evolved separately from dinosaurs and developing their own unique characteristics, including feathers, wings and a unique lung and locomotion system."

"We aren't suggesting that dinosaurs and birds may not have had a common ancestor somewhere in the distant past," Quick said. "That's quite possible and is routinely found in evolution. It just seems pretty clear now that birds were evolving all along on their own and did not descend directly from the theropod dinosaurs, which lived many millions of years later."


Scarce comfort to someone who believes that all species of living creature sprung fully formed from Jehovah's forehead.

Your 2nd link is much more problematic; it points to a site named Evolution News and Views which is an Intelligent Design/Creationist site. The "peer-reviewed" study they discuss is a paper that appeared in the International Journal of Design & Nature and Ecodynamics, a frequent instrument of creationist propaganda. The IJDNE is published by the Wessex Institute of Technology, itself a hotbed of Intelligent Design agitprop. The author of the study, a certain A. McIntosh, is a well-known creationist - and I believe a Young Earth Christian - who is on the editorial board of that same IJDNE. One of IJDNE's editors is Stuart Burgess, another notorious YEC. The IJDNE is a firinge publication; according to WorldCat, not a single library in the UK, US or Australia carries it.

The "irreducible complexity" argument advanced by McIntosh is just more god-of-the-gaps nonsense that has been convincingly refuted by others. No serious scientist outside the blinkered biblical-literalist world ever talks about irreducible complexity as all it says is that "this is too hard for me to understand, Jehovah must have done it." (Actually what it really says is, "Wow, this is so complicated maybe people won't laugh at me if I claim Jehovah did it.)

McIntosh goes on to make the usual ID noise about the incompleteness of the fossil record - the fossil record will/can never be complete enough for you guys.

Citing the OSU study, McIntosh concludes that "even if one does take the fossil evidence as the record of development, the evidence is in fact much more consistent with an ab initio design position - that the breathing mechanism of birds is in fact the product of intelligent design." That's typical creationist reasoning - the OSU people draw no such conclusion - and once more illustrates how logic is a tool very much at the service of religious dogma.

McIntosh jumps all over the place, dragging out all the old tired arguments from the ID world, clearly showing that the whole purpose of his op-ed piece is to lend a patina of rationality to the creationist agenda, to buck up the spirits of his fellow believers.

McIntosh, the IJDNE, and the site you linked to, which reviewed his study, are all part of the hermetically-sealed ID world. A self-contained little bubble of self-referential links and studies that no one outside that world takes seriously.

Time and again we've seen you provide links that turn out to be highly dubious. That you even came across a fringe publication like the IJDNE indicates where you're coming form; you wouldn't even know it exists if you didn't habitually frequent like-minded sites in search of moral support.

quote:
I don't need for Darwinism to be false in order to have Christian beliefs.....Frankly, I just don't see the evidence for Darwinism. It is a fantastic tale that is not backed up by any real evidence.


You don't see the evidence because you don't want to. If there is one thing in all I've said in these many exchanges of ours that I'd like you to give serious consideration to, it's this: it is not intelligence that distinguishes skeptics from creationists, it's personality. When you claim to reject evolution because you find the theory unconvincing, do you think you are more intelligent than all the scientists and laymen who are convinced of evolution's validity - is it your opinion that superior intelligence determines adherence to the creationist camp? The skeptic looks at the evidence and has no emotional investment in where that evidence leads; the theist - esp the biblical literalist - on the other hand, will have god at all costs; for the believer, evidence is a mere afterthought, an inconvenience to be managed.

Your views on evolution are transparently contingent on your religious worldview. I repeat, if the OT said Yahwei directed the rise of species via natural selection, you'd be the forum president of the Darwin Fan Club. That you troll the web desperately looking for studies to provide intellectual cover for you OT literalism, while ignoring all the clear evidence for evolution, clearly puts the lie to the above claim.

Way back, I thought you were just propagandizing with this OT stuff, but you really have convinced yourself of the reasonableness of this garbage. The idea that some kind of superior intelligence was involved in the creation of the universe is at least logically defensible; however, this flat-earth denial of evolution is so willfully ignorant that it takes the breath away. Even the Catholic Church is at pains to distance themselves from this rubbish, lest they lose all credibility with those Catholics who chose to use their brains for something other than memorizing biblical quotes; but you guys persist in this - the human mind is truly an astounding thing.


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