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Author Topic:   Mammalian Middle Ear Evolution
RAZD
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Posts: 19878
From: the other end of the sidewalk
Joined: 03-14-2004
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Message 16 of 25 (484697)
10-01-2008 12:46 AM
Reply to: Message 15 by NosyNed
09-30-2008 10:03 PM


Re: What is predicted by ToE
LOL - posting late and tired. 240Myr.
This message is a reply to:
 Message 15 by NosyNed, posted 09-30-2008 10:03 PM NosyNed has not yet responded

  
PaulK
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Posts: 15069
Joined: 01-10-2003
Member Rating: 3.2


Message 17 of 25 (484699)
10-01-2008 1:24 AM
Reply to: Message 12 by AlphaOmegakid
09-30-2008 6:28 PM


Re: Serious misunderstanding...
quote:

Are you laughing at your own mistake.

No, I said you couldn't work out when the DDME appeared without fossil evidence or an equivalent and you tried to disagree - by citing fossil evidence.

quote:

Now my question is what is the prediction of ToE about when the DDME ear evolved? If it can predict Tiktaalik, can't the theory predict the first DDME find?

Not without adequate evidence to do so. The evidence that you have cited is quite insufficient to make a good prediction. All we can say us some time after the first mammals - without a good way to date the first mammals.

quote:

Does ToE based on the fossil evidence of the ear and jaw predict that the DMME evolved sometime after 125mya, before 125mya, closer to 70mya

The evidence that you cited is completely insuffucient to say for reasons that you claimed to understand. Unless you are trying to trick someone into mistakenly making a prediction on inadequate evidence there is something very wrong here.


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Dr Jack
Member (Idle past 275 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 18 of 25 (484708)
10-01-2008 5:04 AM
Reply to: Message 8 by AlphaOmegakid
09-30-2008 5:36 PM


The ToE of equivocation
quote:
What I am trying to establish is does ToE actually make any predictions. Or does it just morph the theory to the data?

I think the term ToE is largely misnomer.

There isn't a theory of Evolution instead it is a body of knowledge. What is usually meant by 'the Theory of Evolution' is (the modern synthesis of) what Darwin called Natural Selection. This is a theoretical statement about how Evolutionary change is caused. It makes predictions; but these predictions are not ones that can be tested by the timing of the MME.

But alongside Natural Selection you also have the reconstructed history of life on Earth; and this includes a whole body of various theories about when specific changes happened and further theories about what caused the changes. Because these are based on generally weak and constantly updating evidence they change rapidly; and they do make predictions: from the fossils we have already discovered charting the history of the MME we can make predictions about what fossils we'll expect to find in the future and what timeframe we should find them in (and also about genetics and embryology, but that's another story).

So, you're right, the ToE does make predictions about when we should find fossils of transitional MMEs; but the others are also right, the ToE doesn't make predictions about these transitionals. It depends on what you mean when you say ToE.

Edited by Mr Jack, : Better title


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Percy
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Posts: 18488
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.8


Message 19 of 25 (484709)
10-01-2008 6:01 AM
Reply to: Message 18 by Dr Jack
10-01-2008 5:04 AM


Re: The ToE of equivocation
I found this post very confusing.

About the "theory of evolution" as a label, you think it's a mismomer?

About Darwin's definition of evolution, you don't you he would have included descent with modification along with natural selection?

About predictions of the TOE, you think there are two meanings, and one makes predictions and the other doesn't?

It feels like you're trying to say something I should already know and understand and likely agree with, but I can't figure out what it is.

--Percy


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 Message 18 by Dr Jack, posted 10-01-2008 5:04 AM Dr Jack has responded

Replies to this message:
 Message 20 by Dr Jack, posted 10-01-2008 6:18 AM Percy has responded

    
Dr Jack
Member (Idle past 275 days)
Posts: 3507
From: Leicester, England
Joined: 07-14-2003


Message 20 of 25 (484710)
10-01-2008 6:18 AM
Reply to: Message 19 by Percy
10-01-2008 6:01 AM


Re: The ToE of equivocation
If you'll excuse me quoting myself from elsewhere, I once wrote a longer breakdown of the theory:

quote:
What exactly is Evolution?

In this discussion, I shall assume we're talking about Biological Evolution or The Theory of Evolution rather than any of the other meanings of the word 'evolution'. I've also chosen to leave out the evidence from this answer, we can discuss that later as you see fit.

Evolution is the scientific theory developed from Darwin's work Origin of Species - the central theme of which is decent with modification by natural selection. It's a big subject so I'll break it into pieces.

The first part is Descent with Modification. This simply says that a creatures children are similar but not identical to their parents. In Darwin's time, no mechanism was understood for this process. Modern genetics allows us to understand how it works, and we can now track the transfer and alteration of genes. Genetic copying is not perfect, so each generation contains a small number of errors (which we call mutations).

The central part of the theory is the mechanism proposed by Darwin: Natural Selection. Natural Selection is really very straight forward, it says that individuals that are more successful will come to dominate the population. In practical terms the success of an organism can be measured by the number of grand-children it has (grand-children rather than children because having lots of children who die young or never breed is no use). It should be obvious that organisms that are having more grand-children will end up forming a larger portion of the population than those who are having fewer. Note that this success (known as fitness) may not correspond to what we would subjectively identify - for example, the fittest bear may not be the biggest and strongest because their energy needs are higher and they could suffer in times of drought.

This is, of course, complicated by sexual reproduction. In each generation, most organisms do not produce exact copies of themselves but mix their genes in with another's. So what, in fact, we should be looking at is the effect of genes (and the traits they cause) on the success of an organism and what Natural Selection is doing is increasing the proportion of the population that carry the given gene - this is what Dawkins is talking about when he uses the term 'Selfish Gene'.

When we combine Descent with Modification and Natural Selection we get Evolution. The theory is that over time mutation (and genetic recombination) will produce new solutions to problems (faster running, better wings, better eyesight, etc.) and that Natural Selection will constantly keep picking the one that works best. Now this level of Evolution is not particularly interesting, so far we've got dogs that run slightly faster than their forebears and moths that are a darker shade in industrial cities. The big claim made for evolution is that this mechanism is sufficient to explain the apparent design we see in all life today, including such marvellous examples as an eye, a bird's wing or an ant's social structure. An important point to remember is that evolution is not directed, there is no end goal. At any time it is simply picking what works best. This strictly limits the solutions that evolution is capable of finding since each one must be a step-wise improvement (or at least neutral with respect to fitness).

And this is were we come to the third portion of Evolution: Common Ancestry. Common Ancestry is the claim that similar organisms today evolved from common ancestors in the past (this is a slightly different claim from the Single Common Ancestor claim I will discuss below), so Coyotes and Wolves evolved from a now extinct Canid, Zebras and Horses from an extinct Equid and humans and chimps from an extinct ape. The evidence for Common Ancestry comes from two main sources: the fossil record and genetic analysis.

Most evolutionists believe that all life on earth evolved from a Single Common Ancestor, all believe that all animals evolved from a single common ancestors. According to Evolution we can construct trees of ancestry going back into the past, the further we go back the more the species alive today will converge in their ancestry. For instance, all mammals and reptiles converge to a single ancestor around 500 million years ago - the first vertebrate. The direct evidence for Single Common Ancestry lies in the use of DNA throughout all living creatures (viruses, incidentally, are not commonly thought of as alive - although I think they should be - scientists differ on whether viruses and all other life share a common ancestor), the indirect evidence comes from the simple convergence of evolutionary trees which, if extrapolated, leads inevitably to a single point of convergence. If Single Common Ancestry turned out to be false that would not scupper evolution as a whole. This is not true for either of the three points above.

The final areas of Evolution are Historical Evolution and Non-adaptive Selection. Historical Evolution is the attempt to reconstruct as exactly as possible the actual evolutionary pathways that led from one species to another, and establish the relationships between existing species. Non-adaptive selection deals with genetic change in populations which is not linked to an individuals adaptedness: this includes things such as genetic drift as well as events such as lightning strikes and volcanic explosions.


What I'm saying is that when Nosy says the Theory of Evolution does not make predictions about when the MME evolved, he is talking about the Descent With Modification and Natural Selection parts; but what AOK is talking about is the Historical Evolution part. Now the existing historical reconstructions of what exact path evolution took do make predictions about what fossils we will find and when but if these predictions turn out to be wrong all that will be disproved is that part of our understanding of the history of life on earth.

Is that any clearer?

Edited by Mr Jack, : No reason given.


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 Message 19 by Percy, posted 10-01-2008 6:01 AM Percy has responded

Replies to this message:
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Percy
Member
Posts: 18488
From: New Hampshire
Joined: 12-23-2000
Member Rating: 2.8


Message 21 of 25 (484713)
10-01-2008 6:45 AM
Reply to: Message 20 by Dr Jack
10-01-2008 6:18 AM


Re: The ToE of equivocation
Okay, I see what you're getting at, but I find the way the argument is structured very confusing, and aspects of it seem misleading, even wrong when in the previous message you implied there are two different ToE's. Maybe I'm the odd evolutionist out, but if other evolutionists are having this much trouble understanding your point, then creationists are really going to have trouble.

I see what you're calling Historical Evolution merely as the interpretation of evidence in the context of the ToE. When, for example, paleontologists are willing to make specific pronouncements based upon ambiguous or insufficiently complete evidence then they practically guarantee they will be overturned or in some way invalidated, and I think one of your points is that such occasions have nothing to do with the validity of the ToE, just as a police lab technician reaching incorrect conclusions could not affect the validity of chemistry.

--Percy


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Wounded King
Member (Idle past 2265 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 22 of 25 (484716)
10-01-2008 7:36 AM
Reply to: Message 14 by RAZD
09-30-2008 9:18 PM


Re: What is predicted by ToE
Those are the "diagnostic traits" of mammals, and it includes the ear.

It includes changes to the ear but not those changes which would produce what is termed the definite mammalian middle ear (DMME) in which the connection to the mandible is entirely lost when Meckel's cartilage is absorbed. It is this specific change that AOK seems to be focusing on and for which Yanoconodont is presented as an intermediate form.

TTFN,

WK


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 Message 14 by RAZD, posted 09-30-2008 9:18 PM RAZD has responded

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 Message 23 by RAZD, posted 10-01-2008 9:24 PM Wounded King has responded

    
RAZD
Member
Posts: 19878
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.6


Message 23 of 25 (484820)
10-01-2008 9:24 PM
Reply to: Message 22 by Wounded King
10-01-2008 7:36 AM


Re: What is predicted by ToE
Thanks Wounded King,

... the connection to the mandible is entirely lost when Meckel's cartilage is absorbed. It is this specific change that AOK seems to be focusing on and for which Yanoconodont is presented as an intermediate form.

So we are looking for something between this guy ...

(1) 75 million year old shrewlike mammal

Bad News for Dinos Was Good News for Mammals

quote:
The fossil of a shrewlike animal uncovered a decade ago in Mongolia's Gobi Desert set off one of the most extensive probes ever into the origins of placental mammals, the vast majority of all living mammals (which excludes marsupials and egg-layers, like the platypus).


Click to enlarge

THE SKULL THAT STARTED IT ALL: This skull, belonging to a shrewlike animal, that dates back more than 70 million years, kicked off a comprehensive fossil analysis that led to a determination that placental mammals arose roughly 65 million years ago.
ILLUSTRATION: PAUL BOWDEN/CMNH

To properly age and classify the Mongolian fossil Maelestes gobiensis, estimated to be between 71 million and 75 million years old, Wible and his team compared it with 409 features culled from the skulls, teeth and skeletal remains of other animals ranging in age from present-day mammals to those estimated to have lived over 100 million years ago. In an attempt to determine whether it was a placental mammal, the scientists constructed a tree charting the evolution of placental mammals beginning well in the Cretaceous. "We wanted to find out what our fossil was," Wible says, "and we wanted to test whether any of [the other] Cretaceous fossils could be placentals."

Wible and his colleagues report in Nature that when they finished analyzing and classifying the specimens, they discovered that none dating back to the Cretaceous appeared to be placental mammals; it seemed such mammals more likely evolved some 65 million years ago, which would support the long held "explosive model'' theory that a dino die-off made way for them to spring up.


That talks about another diagnostic characteristic of modern mammals, but not about the ears. The skull however looks like mammal ear structure from what I can see with the jaw and the arch.

... and this guy?

(2) 195 million year old shrew-like mammal(iform?)

Oldest mammal is found: Origin of mammals is pushed back to 195 million years

quote:
Discovery of the skull of a shrewlike animal the size of a paper clip pushes back the origin of mammals, including humans, to 195 million years ago. Found in China, the tiny skull shows evidence that the first mammals evolved from reptiles 45 million years earlier than widely believed.


Click to enlarge

A model of a shrewlike creature that may have been the first true mammal, the most distant ancestor of the class of animals that includes present-day elephants and humans. The reconstruction was made from a 195 million-year-old fossil skull (above right). It was no bigger than a paper clip and weighed less than an ounce.

"Previously, the remains of the first true mammals were only found in deposits 150 million years old," significantly younger than the newly discovered skull, notes Alfred Crompton, Fisher Research Professor of Natural History at Harvard University.

New jaws, ears, teeth

The little almost-mammal weighed a scant 2 grams, considerably less than an ounce. Crompton suspects that it was warm-blooded and possessed hair, although that cannot be proven. H. wui probably was too small to eat anything but insects. It was, in turn, eaten by lizards and other reptiles. According to the accepted definition, mammals have three linked bones in the middle ear, part of the apparatus that translates vibrations of the air into nerve signals that register as sound in the brain. H. wui has these bones, which are believed to have once been part of the jaws of reptiles.

Mammals are also defined by a lower jaw consisting of a single bone that both holds teeth and forms a joint with the upper jaw. In contrast, reptiles have many bones in their lower jaws, some of which make up the jaw joint. A series of fossils, dating back 200 years, show these latter bones becoming smaller and smaller. Paleontologists believe these bones eventually migrated to the middle ear, but until now, no good evidence of this existed. H. wui fills this gap and shows that we hear with bones that once formed part of the jaws of reptiles.

However, he and his colleagues are cautious about making claims for H. wui's position on the evolutionary ladder. "Not everyone will agree with our interpretation that the skull represents the oldest relative of mammals, a species that lived as long ago as 195 million years," he admits. There will be controversy until more fossils like it are found in rocks as old.


I note that they don't mention your cartilage, and this picture is even harder to see any detail on.

On the other hand, AlphaOmegaKid's Yanoconodon seems a little younger but not necessarily more advanced than H. wui above.

quote:
Yanoconodon is a monotypic genus of extinct early mammal whose representative species Yanoconodon allini lived 125 million years ago during the Mesozoic in what is now China. It is considered to be a transitional fossil due to the formation of its middle ear, which is a cross between those of modern mammals and their nearest relatives, the mammaliaformes. Yanoconodon was a Eutriconodont, a group synonymous to the Triconodonts which lived during the time of the dinosaurs. Indeed, some such as Repenomamus grew so large that they were able to eat small dinosaurs in some cases.[1] In particular, Yanoconodon is considered to be closely related to Jeholodens.[2]

One begins to wonder how many (very?) different organisms can be described as "shrew-like" ...

Enjoy


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This message is a reply to:
 Message 22 by Wounded King, posted 10-01-2008 7:36 AM Wounded King has responded

Replies to this message:
 Message 24 by Wounded King, posted 10-02-2008 4:30 AM RAZD has acknowledged this reply

  
Wounded King
Member (Idle past 2265 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 24 of 25 (484836)
10-02-2008 4:30 AM
Reply to: Message 23 by RAZD
10-01-2008 9:24 PM


Re: What is predicted by ToE
So we are looking for something between this guy ...
[...]
... and this guy?

Not really. H. wui is the same as Hadrocodium which I mentioned in Message 11, The paper describing H. wui (Luo et al., 2001) definitely does mention Meckel's cartilage ...

Luo et al. writes:

The fourth feature is the absence of the meckelian sulcus in the mandible of Hadrocodium (Fig. 3D). In living mammals, this sulcus is lost in the adult after the reabsorption of the anterior part of the Meckel’s cartilage, which would be associated with the meckelian sulcus on the dentary during embryonic stages

So there is strong evidence for a detached middle ear already in H. wui. So a common ancestor showing an intermediate middle ear, if that is what we are looking for, should have been extant before ~195 MYA.

I'm not sure what the point of this line of thought is though since Yanoconodon shows us exactly what we would expect that intermediate middle ear morphology to look like with all the ossicles developed but the malleus is still attached to Meckel's cartilage when the cartilage ossifies.

Given the fact that Hadrocodium was already mentioned in his references one has to wonder if AOK was trying to pull a fast one; getting people to state that ToE would predict a date after Yanoconodon appears in the fossil record for the first appearance of the DMME so he can then whip out Hadrocodium and say 'ah hah! This feature appears in the fossil record almost 100 MY before Yanoconodon, therefore evolution is false!'.

One begins to wonder how many (very?) different organisms can be described as "shrew-like" ...

Pretty much all of the early mammaliaforms.

TTFN,

WK


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 Message 23 by RAZD, posted 10-01-2008 9:24 PM RAZD has acknowledged this reply

    
Wounded King
Member (Idle past 2265 days)
Posts: 4149
From: Edinburgh, Scotland
Joined: 04-09-2003


Message 25 of 25 (485212)
10-06-2008 11:40 AM
Reply to: Message 12 by AlphaOmegakid
09-30-2008 6:28 PM


Hey AOK, did you get your answer?
Hi AOK,

Do you think you have a satisfactory answer to your OP now?

TTFN,

WK


This message is a reply to:
 Message 12 by AlphaOmegakid, posted 09-30-2008 6:28 PM AlphaOmegakid has not yet responded

    
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