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.
|
The existence of the platypus is proof that if evolution doesn't existt then God has a wicked sense of humour.
Both the platypus and the giraffe were designed by a committe of LIBERALS....
Nah! Couldn't be.
But they look so cute and nice...
God has a wicked sense of humour!
It will be lawyered to death, much like the continued existence of monkeys and fish, and Archaeopteryx who could fly being older than the Chinese feathered dinos which could not.
I had to stop to look at a platypus thread. You never know what you will find of FR.
Yes, it does. But we go where the facts lead us.
How bizarre is it that of an entire subclass of mammals, the two surviving representatives (platypi and Echidnae) are so bizarre?
Liberals, too.
Evolved twice? Give me a break. Do people really not understand that evolution involves random mutations and then the death of all non-mutated individuals and their offspring?
The fact is that intelligent people believe in evolution because they believe that intelligent people believe in evolution. (Think about that one for a moment).
We each have a brain to think for ourselves. Most people, for example, aren't aware that after nearly 50 years of intensive efforts, science abandoned laboratory efforts in the late 90's to create the simplest precursors to a living organism. Yet they continue to cling to the notion that such a process occurred by itself over billions of years.
Let's say you gathered all the parts of a watch -- crystal, springs, gears, hands, etc. (which is far less complex than the simplest organism) -- and threw them at your wrist. Do you think they would EVER assemble themselves into a functioning watch? Or how many times would you have to throw your shoelaces at your shoes before they laced themselves up?
THINK for yourself !! Evolutionists have a viewpoint that is as tenacious as a religion.
The Real Science is so simple, anyone can do it.
For a single example, a birth defect in which some part of the fetus fails to develop fully can't be ruled out.
~Simon Conway Morris (New Scientist Nov 2002)
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.