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.
It doesn't. Superdogs don't come from herds of elk.
You are not paying atention to the numbers. Numbers of years and the numbers of offspring. After a few years, our elk's offspring are spreading his genes and he still is too. If you think about it, a beneficial gene can go through a population very rapidly sexually. In a large population, that elk gene could spread to 100,000 in 10 years. If he's asexual there might be 20. The advantage for sexual reproduction is obvious.
No super dog will emerge. The breeds are artificial and are not separate species which you seem to imply (actually I can't figure out what you meant there - therefore the word "blather"). BTW, the Chihuahua is one of the closest breeds by DNA homology to the wild wolf (a recent study reported in Science News) even though they look more like an overgrown rat to me.
I thought that war "fury" not venom.
Makes you pine for the effdot days when stupid posts were cryptic. The current crop removes all doubt.
And it's lactation, which is quite different in form from that of other mammals, is the main reasons for calling it a mammal. Maybe the monotremes should be raised to the level of a distinct Class?
The highlighted statement is not correct. There is no requirement that a new species' ancestor species go extinct.
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.
The TOE does not cover where life came from.
Yes, "Hell hath no fury like a woman scorned", but does the venom have to be organic?
Remember Clint Eastwood and "Misty"
When I was a kid, I always questioned why monotremes were lumped with placentals and marsupials under the "Eutheria" category when it seemed so much more obvious to me that they should be classified as the last surviving theraspids instead. Of course, I also thought that hyaenas were related to bears and dogs instead of cats and civets, that mudskippers were close to ancestors of amphibians, etc, and learning about the common jaw and ear structure between the mammal types (something which Ichneumon has posted on the crevo lists before) temporarily put that piece of adolescent armchair theorizing to rest. But now....
It's pretty interesting not only how venomous creatures are so much more common in island populations, but they tend to be so much more dangerous than their counteparts. The most venomous snakes in the world are found in Australia and the only poisonous bird found to date lives in New Guinea. There's a question which I'd love to see evolutionary epidemiologists tackle; I'm sure there has to be an adaptationist explanation for this.
" (most mutations are recessive). "
Well, just not true (back to that Biology Book). So our theoretical elk is a homozygous recessive? How did that happen? And besides even if the trait is recessive, when our bull elk's kids start mating in a few years, homozygous recessives will emerge, not in "thousands of years or generations" (paraphrased from your post), but in only a few years. I don't know where you live, but randy bull elk are the norm not the exception.
BTW to your quote above. Most mutations leave no noticeable effect on the organism, not because they are recessive but because they do not significantly affect the gene product.
Thanks for the ping!
"explain speciation is the lack of mutagens."
Mutations occur randomly at particular frequencies (typical frequencies are 10^-6 to 10^-7) without mutagens. All mutagens do is increase the frequencies of natural mutations.
IOW you don't need mutagens to get mutations.
I am sure, from a strict viewpoint, that you are correct that the theory of evolution doesn't cover the origin of life-- however I am also sure that you know as well as I do that the way in which it is taught in school and presented in popular sources results in the vast majority of people believing that it does. This result is not accidental.
Personally, I don't see any reason why the theory of evolution has to stand in opposition to the existence of God, but even so, I don't believe in it in any but a micro way. I don't think the evidence supports it, and the rabidity of belief among supporters is so insistent, and so intent on calling the other side stupid that I think the hubris will catch up with them. Sooner or later, I think the zeitgeist will shift, more evidence pointing the other direction will be found, and the theory will be utterly discredited. But, we'll see. ;)
Are you sure? The State of New York has one for a junior Senator.
Most problems of the spine and neck are due to neglect or an injury from a traumatic event. Spines don't just become misaligned or damaged from a walk in the park, you know.
Okay, I'll buy that...but what causes the process to happen? Is it slight inaccuracies in gene transfer at meiosis?
Also...what does it take to get a population of animals that are cross-fertile with one another, but no longer cross-fertile with other descendants from their ancestral line?
Your right, I mean platypus(i)(es) aren't as popular as Meerkats, weasels and/or skunks (unless you a liberal Democrat/RINO, on last two) or some other Disney animated cartoon character.
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