The jaw of Teinolophos trusleri catches the ear bones in the act of separating from the jaw.
Posted on 02/11/2005 6:49:09 AM PST by PatrickHenry
Triple bone structure arose independently in platypus and humans.
Listen up: mammals seem to have evolved the delicate bone structure of the middle ear at least twice. The surprising discovery comes from a fossil, found off the southern coast of Australia, that belongs to an ancestor of the platypus.
Modern mammals are unique among vertebrates for possessing three tiny bones in the middle ear. The malleus, incus and stapes (commonly known as the hammer, anvil and stirrup) work as part of a chain that transmits sound towards the skull. Birds and reptiles have only one bone to perform this function.
Because the mammalian arrangement is so complex, scientists believed that the set-up had evolved on just a single occasion, in an ancestor that gave rise to placental animals (including humans), marsupials and monotremes (such as the duck-billed platypus).
All this changed when James Hopson, a vertebrate palaeontologist at University of Chicago, Illinois, took a trip to Australia. There he met a team of researchers including Thomas Rich of Museum Victoria in Melbourne.
The jaw of Teinolophos trusleri catches the ear bones in the act of separating from the jaw.
Rich and his colleagues had recently unearthed a fossil of Teinolophos trusleri, an ancestor of modern monotremes that lived 115 million years ago. "He said he had some new Teinolophos specimens and when he showed them to me I almost fell off my chair," says Hopson, an author of the study, published this week inScience [Rich T. H., et al. Science 307, 910 - 914 (2005)].
Hammer time
Palaeontologists believe that the middle-ear bones of modern mammals once belonged to the jawbone and later separated to adopt their present location. This is supported by the fact that the middle ear's bones associate with the jaw in the early development of modern mammalian embryos.
What makes theTeinolophos specimen surprising is a large groove in its adult jawbone, which indicates that the smaller bones had not yet detached.
Teinolophos lived after monotremes split from the placental and marsupial mammalian groups. Its jawbone structure, along with its place in the evolutionary tree, hints that a common ancestor to all these mammals lacked the special three-bone ear structure.
This means that natural selection must have driven the same rearrangement in independent groups, after the monotreme split. "Some embryologists had the idea that it might be convergent but nobody really believed this," says palaeontologist Thomas Martin of the Senckenberg Research Institute in Frankfurt, Germany. "I was quite shocked when I heard that such a complex morphological transformation happened twice."
The discovery will compel many experts to rethink their appreciation of mammals' common evolutionary heritage. "Until now it was considered to be one of the most important shared derived characteristics of modern mammals," says Martin.
Fictional Placemarker
Glass of milk
Standing in between extinction in the cold
and explosive radiating growth
So the warm blood flows
Through the large four-chambered heart
Maintaining the very high metabolism rate they have
Mammal, mammal
Their names are called
They raise a paw
The bat, the cat
Dolphin and dog
Koala bear and hog
One of us might lose his hair
But you're reminded that it once was there
From the embryonic whale to the monkey with no tail
So the warm blood flows
with the red blood cells lacking nuclei
Through the large four-chambered heart
Maintaining the very high metabolism rate they have
Mammal, mammal
Their names are called
They raise a paw
The bat, the cat
Dolphin and dog
Koala bear and hog
Placental the sister of her brother Marsupial
Their cousin called Monotreme
Dead uncle Allotheria
Mammal, mammal
Their names are called
They raise a paw
The bat, the cat
Dolphin and dog
Koala bear and hog
The fox, the ox
Giraffe and shrew
Echidna, caribou
"I presented showing that there are many cases of "multiple evolution events"- any one of which would be "troubling" and improbable."
I devasted your claim of improbability. I mentioned the genetic "switch" that turns on and off the formation of wings in insects.
You ignored it. But that one piece of data makes your argument from personal incredulity, with NO supporting evidence, void.
What?!?
There is no such thing as a Liberal Creationist?
I find that hard to believe!
Tell that to VR!
He didn't call YOU a pedophile: the court did - to that defrocked Catholic priest who just got 18-20.
Well... ...it just depends on how someone INTERPRETS that verse, doesn't it??
;^)
Well... that sure PROVES it then!
I dealt with that when I told you what my problems are with data anomaly soup. Here's an even higher level summary.
The Earth is wide and it's got a 4.5 billion year history. Something improbable figures to be happening somewhere all the time. You can make lists of improbable things till the cows come home and nobody's going to admit your list as proof of the alternative theory you didn't present because it was too flipping goofy.
I pity the kids who had to learn science from you. You are openly hostile to the spirit of inquiry. A you-can't-make-me-see-ist, nothing-I-don't-like-proves-anything-ist dumb-bleep teaching science! Sometimes the foxes get hired to guard the henhouse. It happens.
VR knows science quite well. Perhaps you do not understand the import of his comments, or the frustration scientists feel in dealing with the bad faith tactics of creationists.
His implication is that anyone who disagrees with his ridiculous interpretation of the Bible, anyone who understands science is a pedophile.
He used the fact that I am a Christian Minister as an argument against my ability to know the truth of reality that science shows. This is, of course, absurd.
He used the type of emotional extortive argument that all creationists find necessary in lieu of any actual evidence for their positions. The reason they must threaten scientists and Christians who understand the science is true is simply because the Scriptural basis for the creationist position is not there.
In a recent post I destroyed Havoc's silly idea that there was a definite article in front of the sequence of days. He was using a mistranslation by the KJV translators and a misunderstanding of various biased commentators to try to bludgeon me in to submitting to a nonsensical interpretation of Scripture.
Each of the creationist positions "based" on Scripture is similarly flawed. In fact, the Biblical, religious and theological basis for creationism is weaker than the scientific basis. Sadly, there is no evidence for the creationist science position, so one can only imagine the vacuity of the Biblical position. How can something be less than a vacuum? Only the creationists will be able to explain that one using illogic, twisted definitions and rhetorical trickery.
And when two lovers coo,There will always be gaps in the knowledge. There will always be some funny misfit data items.
They still say, "I love you."
On that you can rely.
No matter what the future brings,
As time goes by.
You can't make a theory just by claiming gaps in the evidence trail are gaps in history and saying the misfit data items are proof of magic.
(But I do follow science news avidly. Used to write a lot of SF.)
Yeah, now that Saddam's sons are dead.
Aren't our thumbs getting progressively longer, and our heads bigger? Aren't a significant number of humans being born even today with vestigial tails?
I'm still waiting for archeological finds of chairs with holes in the seats.
Evidence for evolution exists, of course. But it only adds to the ever-unfolding majesty and mystery of creation.
(will we soon have to redesign the cigarette lighter and the doorknob?
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