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Author Topic:   Marsupial evolution
Pete OS
Junior Member (Idle past 4411 days)
Posts: 31
Joined: 04-26-2007


Message 1 of 91 (398273)
04-30-2007 1:10 AM


It is often said, it support of evolution, that the marsupials are "more similar" to each other then to their similar looking placental counterpart. This was one of the major lines of evidence that convinced me of evolution. But I would like to dig deeper into this. When scientists say they are more similar, to they refer to bone structure or genetic similarities? Indeed, these must both be true if in reality they evolved from a more recent common ancestor then they share with the placentals; but exactly which lines is more obvious to scientists? Is there a site where the specific evidence is drawn out, perhaps with pictures of the bone structures or descriptions of similar mutations in non-coding dna shared by the marsupials but not the placentals?

Thank you.


Replies to this message:
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AdminNosy
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Message 2 of 91 (398278)
04-30-2007 1:40 AM


Thread moved here from the Proposed New Topics forum.

  
Modulous
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Posts: 7789
From: Manchester, UK
Joined: 05-01-2005


Message 3 of 91 (398285)
04-30-2007 3:46 AM
Reply to: Message 1 by Pete OS
04-30-2007 1:10 AM


When scientists say they are more similar, to they refer to bone structure or genetic similarities?

Both. In simple terms placentals and marsupials differ in their morphology, the epipubis is apparantly a dead giveaway.

Genetically, a marsupial mouse is closer to a kangaroo than it is to a placental mouse. An interesting thread that covered this issue can be found here - I give you the last post, because it is only the last half of this thread that goes into it, so work backwards. A better, but shorter thread might be Sequence comparisons (Bioinformatics?).

but exactly which lines is more obvious to scientists?

With both the genetic and morphological data in front of them, I'd imagine the genetic data would be much more obvious. However, the genetic data is a little harder to get hold of :)

Hopefully that should start you in the right direction.


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Doddy
Member (Idle past 4221 days)
Posts: 563
From: Brisbane, Australia
Joined: 01-04-2007


Message 4 of 91 (398290)
04-30-2007 5:27 AM
Reply to: Message 1 by Pete OS
04-30-2007 1:10 AM


Is there a site where the specific evidence is drawn out, perhaps with pictures of the bone structures?

I don't know about a site, but a great book for you to read would be this one:

K.F. Liem, W.E. Bemis, W.F. Walker. & L. Grande. (2001) Functional Anatomy of the Vertebrates: An Evolutionary Perspective.

I hope to get some of this stuff up on the EvoWiki soon, when I have time. I think morphology is a better form of evidence than genetic homology, because it is easier understood by the layman (that is, the people who are most likely to doubt evolutionary theory).


Help inform the masses - contribute to the EvoWiki today!

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Pete OS
Junior Member (Idle past 4411 days)
Posts: 31
Joined: 04-26-2007


Message 5 of 91 (398390)
04-30-2007 2:48 PM
Reply to: Message 3 by Modulous
04-30-2007 3:46 AM


Thank you Modulous. This is a good start. I have skimmed over the Bioinformatics thread and it does indeed look like the sort of genetic evidence evolution would suggest, and also, something I might have fun doing! Someday I might see if a laymen like myself can start using this program, it would be fun to make genetic tree of life comparisons of my own.

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Pete OS
Junior Member (Idle past 4411 days)
Posts: 31
Joined: 04-26-2007


Message 6 of 91 (398391)
04-30-2007 2:49 PM
Reply to: Message 4 by Doddy
04-30-2007 5:27 AM


That looks like a textbook that is probably a wee bit over my head (and over my price range!) but thanks for the reccomendation. I see I can get a 1994 version for $3.00 so I might consider that.

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PaulK
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Joined: 01-10-2003
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Message 7 of 91 (398394)
04-30-2007 3:04 PM
Reply to: Message 6 by Pete OS
04-30-2007 2:49 PM


You might want to look into the history. The genetic data is a relatively new thing. Before then and before cladistics, taxonomy was based on morphology alone. Not just the skeletal structure but the soft parts, too.

When an earlier discussion focussed on the skeletal similarities between the wolf and the thylacine, one thing that cropped up was the teeth. Wolves have distinctively canine teeth. Thylacine teeth are quite different. They really are easy to tell apart if you look at dentition.


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Modulous
Member (Idle past 415 days)
Posts: 7789
From: Manchester, UK
Joined: 05-01-2005


Message 8 of 91 (398456)
04-30-2007 8:19 PM
Reply to: Message 5 by Pete OS
04-30-2007 2:48 PM


A little help
This might possibly be of help. It's surprisingly straightforward, really - just gotta get stuck in!

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MartinV 
Suspended Member (Idle past 4140 days)
Posts: 502
From: Slovakia, Bratislava
Joined: 08-28-2006


Message 9 of 91 (398580)
05-01-2007 2:59 PM
Reply to: Message 1 by Pete OS
04-30-2007 1:10 AM



This was one of the major lines of evidence that convinced me of evolution.

Many marsupial mammals have their counterparts in placental mammals. Placental and marsupial moles and placental vs. marsupial wolfs are most striking examples of so called convergence between them.

Skull of marsupial wolf is so similar to skull of canis lupus that only an expert knowing teeth formula of the species can distinguish them.

Such "convergent" evolution prove more evolution governed by law (Nomogenesis or PEH) as darwinistic natural selection as source of it.


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crashfrog
Inactive Member


Message 10 of 91 (398586)
05-01-2007 3:30 PM
Reply to: Message 9 by MartinV
05-01-2007 2:59 PM


Such "convergent" evolution prove more evolution governed by law (Nomogenesis or PEH) as darwinistic natural selection as source of it.

Unfortunately for you such theories were completely disproven by the evidence given in "More Evidence of Evolution - Geomyidae and Geomydoecus".


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PaulK
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Joined: 01-10-2003
Member Rating: 2.9


Message 11 of 91 (398588)
05-01-2007 3:36 PM
Reply to: Message 9 by MartinV
05-01-2007 2:59 PM


quote:

Skull of marsupial wolf is so similar to skull of canis lupus that only an expert knowing teeth formula of the species can distinguish them.

No, you don't have to be an expert if you get a good look at the teeth. I can easily tell them apart. You would need a little specialised knowledge to know which is which - but only a little. The differences are obvious and anyobdy should be able to see them.


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Pete OS
Junior Member (Idle past 4411 days)
Posts: 31
Joined: 04-26-2007


Message 12 of 91 (398601)
05-01-2007 4:35 PM


I think the fact that each marsupial is "closer" both genetically and elsewise to eachother then to its counterpart is striking evidence of a common ancestor. However, the fact that it DID happen that they are so similar to a counterpart is still very strange to me.

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Hyroglyphx
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Posts: 5845
From: Austin, TX
Joined: 05-03-2006
Member Rating: 2.4


Message 13 of 91 (398630)
05-01-2007 8:11 PM
Reply to: Message 1 by Pete OS
04-30-2007 1:10 AM


Don't judge a book by its cover
It is often said, it support of evolution, that the marsupials are "more similar" to each other then to their similar looking placental counterpart.

Kangaroo

Platypus

Koala

Hmmmmm, yes, I see what you mean.

When scientists say they are more similar, to they refer to bone structure or genetic similarities?

Both, usually.

Indeed, these must both be true if in reality they evolved from a more recent common ancestor then they share with the placentals

A degree of morphological similarity does not necessarily indicate an analogous DNA sequence. Or I should say, its not that impressive. What is impressive in the defense of classic Darwinian evolution is shared errors in coding. That lends far more credence than anything else, IMO.

And as you can see, a Tasmanian Wolf has more morphological similarities with its placental counterpart, the Dingo

Dingo

And yet, there is no relation.

Likewise, a Kangaroo Rat, which is a marsupial

looks more like a typical rat or mouse.

And yet, there is no relation. Looks can be deceiving.


"God is like the sun. You can't look at it. But without it you can't look at anything else." -G.K. Chesterton

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anglagard
Member
Posts: 2203
From: Socorro, New Mexico USA
Joined: 03-18-2006


Message 14 of 91 (398636)
05-01-2007 9:06 PM
Reply to: Message 13 by Hyroglyphx
05-01-2007 8:11 PM


Re: Don't judge a book by its cover
FYI NJ, a platypus is a monotreme, not a marsupial. Monotremes lay eggs and have only one hole for peein', poopin', and birthin', like birds and reptiles. Also marsupials have live births, albeit much less developed than placental mammals.

I would use scientific terms here but it is readily apparent you are not familiar with the literature. :laugh:

Edited by anglagard, : add term placental since all are mammals, would hate to be sloppy when criticizing another's sloppiness

Edited by anglagard, : precision.


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Coragyps
Member
Posts: 5407
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 15 of 91 (398637)
05-01-2007 9:33 PM
Reply to: Message 12 by Pete OS
05-01-2007 4:35 PM


However, the fact that it DID happen that they are so similar to a counterpart is still very strange to me.

I don't know just how odd it should seem, but consider that marsupials and placentals all descended from an ancestor that was already in possession of four legs, fur, a particular style of jaw, a three-bone middle ear, live births and milk glands.....quite a lot in common. And consider the wolf and the thylacine: both make/made their living mostly by hunting smallish critters, and relied on being able to gover lots of ground in a day. Both need to be able to snap up a rat-sized meal. How many different ways are there to make a living like that, given the constraints their common ancestry puts on them?


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