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Author Topic:   Marsupial evolution
Blue Jay
Member (Idle past 771 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 76 of 91 (473294)
06-28-2008 4:06 AM
Reply to: Message 75 by randman
06-28-2008 3:36 AM


Re: Empirical studies of convergence
randman writes:

The reason why there should not be pairs is that evolution is supposedly a random process in terms of mutations.

(1) Evolution is not a random process.

(2) Mutation is not evolution.

(3) I have provided a rebuttal to this your “no random duplications” reasoning. Rolling a certain combination of numbers on a set of dice does not render it impossible to roll the same set again later. This shows that it is perfectly within the bounds of probability that random processes can repeat themselves, which falsifies the basis for your line of reasoning, which is “there is no reason to expect a random process to repeat itself.”

(4) You still haven’t made the case that the thylacine and the wolf are all that similar, anyway. All you have is, “they look a lot alike.” I showed you that people can often “look a lot alike,” even when they’re not related, which undermines your point that “looking alike” is in any way meaningful for determining relationships.


Darwin loves you.
This message is a reply to:
 Message 75 by randman, posted 06-28-2008 3:36 AM randman has responded

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randman 
Suspended Member (Idle past 2973 days)
Posts: 6367
Joined: 05-26-2005


Message 77 of 91 (473376)
06-28-2008 4:12 PM
Reply to: Message 76 by Blue Jay
06-28-2008 4:06 AM


Re: Empirical studies of convergence
Evolution is not a random process.

So is it a guided process?

Mutation is not evolution.

So mutatation is't incorporated into the Theory of Evolution? Care to prove that?

a certain combination of numbers on a set of dice does not render it impossible to roll the same set again later. This shows that it is perfectly within the bounds of probability that random processes can repeat themselves,

I hope you are not serious here. Yea, things can happen again. There is an area called statistics dealing with this. The chances of some things occuring are so remote that they are considered to have some cause if they do, repeatedly.


This message is a reply to:
 Message 76 by Blue Jay, posted 06-28-2008 4:06 AM Blue Jay has not yet responded

Replies to this message:
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RAZD
Member
Posts: 19754
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 5.9


Message 78 of 91 (473452)
06-29-2008 11:20 AM
Reply to: Message 77 by randman
06-28-2008 4:12 PM


Re: Empirical studies of convergence
So is it a guided process?

No, it is an opportunistic process.

So mutatation is't incorporated into the Theory of Evolution? Care to prove that?

No, mutation alone is not evolution.

I hope you are not serious here. Yea, things can happen again. There is an area called statistics dealing with this. The chances of some things occuring are so remote that they are considered to have some cause if they do, repeatedly.

Or the calculation that says the chances are remote are questioned (and usually found lacking, due to false assumptions). Statistics cannot prove something cannot occur.

We do know that eyes have evolved several different times and in several different ways. We do know that wings have evolved several different times and in several different ways. Convergent evolution occurs because evolution is opportunistic, and it tends to find practical solutions to problems of survival and reproduction by a process of elimination.

That the general appearance of the thylacine skeleton to the wolf skeleton are similar is not a great surprise -- they are also similar in general appearance to the eohippus skeleton. The details that separate each from eohippus also separate one from the other.

Enjoy.

Edited by RAZD, : .


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This message is a reply to:
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hadar288
Junior Member (Idle past 3822 days)
Posts: 3
From: Dania, FL
Joined: 06-30-2008


Message 79 of 91 (473503)
06-30-2008 9:51 AM
Reply to: Message 77 by randman
06-28-2008 4:12 PM


Re: Empirical studies of convergence
I can't help but notice: You keep referring the the cherry picking of data, yet choose to ignore the evidence that was shown to you that thylacine was observed to stand on its hind legs, use it's tail for balance,jump great distances and to HOP as a form of locomotion. All traits observed in kangaroos.

I'm referring to the post be iceage (message 40) and the link provided:

http://www.naturalworlds.org/thylacine/naturalhistory/behaviour_1.htm

Correct me if I overlooked a previous post of yours.

Edited by hadar288, : No reason given.


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Blue Jay
Member (Idle past 771 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 80 of 91 (473534)
06-30-2008 1:36 PM
Reply to: Message 79 by hadar288
06-30-2008 9:51 AM


Re: Empirical studies of convergence
Hello, hadar288. Welcome to EvC!

hadar288 writes:

You keep referring the the cherry picking of data, yet choose to ignore the evidence that was shown to you that thylacine was observed to stand on its hind legs, use it's tail for balance,jump great distances and to HOP as a form of locomotion. All traits observed in kangaroos.

Well, I think more care is needed here, too: all these traits are most likely also convergent. Kangaroos belong with koalas, Australian possums (not American opossums) and wombats in the order Diprotodontia, whereas the thylacine belongs in with devils, quolls, numbats and marsupial mice in the order Dasyuromorphia (note that none of these animals I've listed are known to have these hopping traits). Given this (which is well-supported by genetic and morphological studies), it's highly unlikely that the hopping traits listed by iceage are actually shared between thylacine and kangaroo.

If they were shared, it would imply that all Dasyoromorphs and Diprotodonts evolved from a hopping ancestor, which, to me, sounds very dubious, if even possible (note that I haven't studied this thoroughly enough to completely rule it out, though).


Darwin loves you.
This message is a reply to:
 Message 79 by hadar288, posted 06-30-2008 9:51 AM hadar288 has responded

Replies to this message:
 Message 81 by hadar288, posted 06-30-2008 4:19 PM Blue Jay has responded

  
hadar288
Junior Member (Idle past 3822 days)
Posts: 3
From: Dania, FL
Joined: 06-30-2008


Message 81 of 91 (473554)
06-30-2008 4:19 PM
Reply to: Message 80 by Blue Jay
06-30-2008 1:36 PM


Re: Empirical studies of convergence
"If they were shared, it would imply that all Dasyoromorphs and Diprotodonts evolved from a hopping ancestor, which, to me, sounds very dubious"

Good point.

As false comparisons go, I would still say it is a better one than fur stripes:)


This message is a reply to:
 Message 80 by Blue Jay, posted 06-30-2008 1:36 PM Blue Jay has responded

Replies to this message:
 Message 82 by Blue Jay, posted 07-01-2008 8:40 PM hadar288 has responded

    
Blue Jay
Member (Idle past 771 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 82 of 91 (473682)
07-01-2008 8:40 PM
Reply to: Message 81 by hadar288
06-30-2008 4:19 PM


Re: Empirical studies of convergence
randman writes:

As false comparisons go, I would still say it is a better one than fur stripes

There are just so many problems with superficial resemblance. Randman has insisted that scientists have not analyzed all features available, yet, he doesn't seem to understand that the reason for the current classification of thylacines as marsupials is because just such deep analyses have been done. I provided a genetics study upthread, and Arachnophilia's skull photos are really still irrefutable.

In a way, randman does have part of a point somewhere, though: he likes to call everything we do in evolutionary biology "assumptions." Some of these things, in fact, are assumptions. But, he doesn't grasp that it doesn't take exhaustive data to uncover a pattern (such as the pouch, double uteri and forked penis of marsupials, as well as the dental formula and the other skull features Arachnophilia presented).

Once you've established the pattern (using, say, fifty marsupial species), all you have to do is look for the hallmarks of the pattern, and you're pretty much guaranteed to be right. And, to lessen the probability of errors, anatomists have done comprehensive studies on key organisms (translation: organisms that people think are important or interesting), and the pattern is built upon and upheld by such studies.

----

For new users:

EvC uses quote boxes to separate what you write from what you quote. There are a few types of quote boxes. Push the "peek" button at the bottom of any post to see the dBcodes you can use to make quote boxes like these:

Bluejay (or write in the name of the person you're quoting) writes:

I like to use this one when quoting other posters.

and

quote:
This one is good for quoting reference materials.

URLs for sources and stuff:

Message #76, upthread, from me. Note, while you're peeking, that, in the "url=" part for a particular post you are referencing, it's best to make the last two numbers (separated by the "#") the same.


Darwin loves you.
This message is a reply to:
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Replies to this message:
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hadar288
Junior Member (Idle past 3822 days)
Posts: 3
From: Dania, FL
Joined: 06-30-2008


Message 83 of 91 (473696)
07-01-2008 11:08 PM
Reply to: Message 82 by Blue Jay
07-01-2008 8:40 PM


Re: Empirical studies of convergence
Bluejay writes:

EvC uses quote boxes to separate what you write from what you quote. There are a few types of quote boxes. Push the "peek" button at the bottom of any post to see the dBcodes you can use to make quote boxes like these.

Thank you. That was driving me crazy.


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carl
Junior Member (Idle past 3639 days)
Posts: 3
Joined: 12-31-2008


Message 84 of 91 (492434)
12-31-2008 9:46 AM
Reply to: Message 1 by Pete OS
04-30-2007 1:10 AM


question from a layman.

did modern placental mammals evolve from marsupials?

they had a common ancestor that presumably didn't lay eggs. what was this ancestor?

i've been searching the web a bit and can't seem to get a straight answer on this.

Edited by carl, : No reason given.


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Replies to this message:
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 Message 86 by Blue Jay, posted 12-31-2008 3:52 PM carl has responded

  
NosyNed
Member
Posts: 8837
From: Canada
Joined: 04-04-2003


Message 85 of 91 (492446)
12-31-2008 12:16 PM
Reply to: Message 84 by carl
12-31-2008 9:46 AM


common ancestor
quote:
Eomaia and Sinodelphys from the Lower Cretaceous of Liaoning (Fig. 3) are the most primitive fossils that can be unequivocally placed onto the placental lineage and the marsupial lineage. Their anatomy presents the ancestral conditions from which the later placentals and marsupials have evolved.

This is from:
http://criticaltransitions.org/poster1.html

It took a bit of googling around to find it.

It appears that it is incorrect to suggest that placentals evolved from marsupials. They did, as you suggest, have a common ancestor.

Now I'd like to know more about what that ancestor was like.


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Blue Jay
Member (Idle past 771 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 86 of 91 (492464)
12-31-2008 3:52 PM
Reply to: Message 84 by carl
12-31-2008 9:46 AM


Hi, Carl. Welcome to EvC!

carl writes:

did modern placental mammals evolve from marsupials?

they had a common ancestor that presumably didn't lay eggs. what was this ancestor?

So, I'm an entomologist, but paleontology and marsupials are two topics I like to read about a lot.

Like Ned said, not much is known about the common ancestor. The primary distinguishing features are reproductive, and those don't fossilize well. So, the fossil record will must likely never tell us much about when marsupials developed the marsupium (pouch) or when placentals developed the placentum.

Obviously, milk glands predate live birth, because monotremes produce milk but still lay eggs. Most likely, the common ancestor retained the eggs inside itself until just before they hatched (ovovivipary), and eventually, simply did away with the "shell" and membranes of the egg, because these were no longer really needed.

Alternatively, the common ancestor may have simply lost the ability to create "shell" and membranes, and the young simply developed on a yolk without a protective shell. This seems highly unlikely to me, though.

But, in the end, we'll have to wait until paleontology and genetics develop the tools (and funding agencies develop the interest) to learn how it really happened.


I'm Bluejay.

Darwin loves you.


This message is a reply to:
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Replies to this message:
 Message 87 by carl, posted 12-31-2008 4:58 PM Blue Jay has responded

  
carl
Junior Member (Idle past 3639 days)
Posts: 3
Joined: 12-31-2008


Message 87 of 91 (492470)
12-31-2008 4:58 PM
Reply to: Message 86 by Blue Jay
12-31-2008 3:52 PM


thanks for your replies mantis and ned. an interesting topic.

was just thinking that when the two lines diverged mammals did not yet appear to have the ability to make a fully-formed placenta. so would that make the common ancestor more like a marsupial than a placental mammal?

Edited by carl, : No reason given.


This message is a reply to:
 Message 86 by Blue Jay, posted 12-31-2008 3:52 PM Blue Jay has responded

Replies to this message:
 Message 88 by Blue Jay, posted 12-31-2008 5:34 PM carl has responded

  
Blue Jay
Member (Idle past 771 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 88 of 91 (492476)
12-31-2008 5:34 PM
Reply to: Message 87 by carl
12-31-2008 4:58 PM


Hi, Carl.

carl writes:

was just thinking that when the two lines diverged mammals did not yet appear to have the ability to make a fully-formed placenta. so would that make the common ancestor more like a marsupial than a placental mammal?

Well, they probably also didn't have a marsupium (pouch), so wouldn't that make them more like a placental mammal?

I think it's going to take a lot more traits than just the reproductive structures to actually find the answer to your question. Likely, the best paleontologists will ever be able to do is compare bone structures, such as dental formulas and the relative shapes and sizes of various bones (as Arachnophilia provided in Message 16 of this thread, but using pre-placental/marsupial mammals for comparison).

I think the consensus so far is that the evidence is ambiguous. Maybe someday a brilliant paleontologist and/or a brilliant geneticist will be able to resolve the question with better tools and more information than we have today.


I'm Bluejay.

Darwin loves you.


This message is a reply to:
 Message 87 by carl, posted 12-31-2008 4:58 PM carl has responded

Replies to this message:
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carl
Junior Member (Idle past 3639 days)
Posts: 3
Joined: 12-31-2008


Message 89 of 91 (492501)
01-01-2009 1:30 AM
Reply to: Message 88 by Blue Jay
12-31-2008 5:34 PM


Well an alternative to placentals evolving from marsupials, I guess, is that is that the marsupials split from a monotreme-like ancestor earlier than the placentals.

That might account for why both the monotremes and marsupials suckle young that seem almost embryonic. It's interesting that the female echidna (the other monotreme) develops a simple pouch in which to lay her egg. The "puggle" is not much bigger than a jellybean when hatched and is carried around in her pouch for about three months.

I do think marsupials are a more ancient lineage than placentals, but, as you say, the fossil record seems to be ambiguous on this.

Thanks for your help on this fascinating subject.

Edited by carl, : No reason given.

Edited by carl, : clarity

Edited by carl, : No reason given.

Edited by Adminnemooseus, : Put upper-case letters where they belong.


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olivortex
Member (Idle past 2852 days)
Posts: 70
From: versailles, france
Joined: 01-28-2009


Message 90 of 91 (497178)
02-02-2009 9:15 AM
Reply to: Message 89 by carl
01-01-2009 1:30 AM


[q] I do think marsupials are a more ancient lineage than placentals [/q]

125 million years is supposed to be the age of the oldest placentals and marsupials found to this day, indeed. Without having gone into details of the discoveries, the fact of carrying the baby outside can be seen as sophisticated but also as primary. I can' tmake an opinion for myself on that, but i find it very interesting


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