Marsupials

Posted by Helen on September 05, 1998 at 19:44:17:

On a long gone post (must have been over 3 hours old!), I was challenged to contact Kurt Wise about his opinion regarding the Davis and Kenyon's remarks in Of Pandas and People mentioning the high degree of similarity between the Tasmanian tiger and the wolf and the dog.

Since I am learning not to be shy, I did. Here is his response:

re: marsupial vs. placental wolves. Although there are differences between these two animals which are a consequence of being marsupial vs. placental, there are rather remarkable similarities between them. According to evolution the marsupials and placentals separated early in mammal history, when neither group looked anything like a dog. Since that time, both groups have evolved a dog morphology -- apparently independently. That such a convergence of form could occur in such unrelated groups is rather unexpected in evolutionary theory. But, the marsupial/placental story only begins with the similarity in dogs. There are marsupial/placental convergences in skunks, flying squirrels, tigers, and even saber-toothed tigers (as well as others). For it to happen once is a bit amazing. For it to happen many times really stretches the credulity of evolutionary theory to the breaking point!

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Posted by Mockingbird1 on September 05, 1998 at 19:53:37:

In Reply to: Trekking with Tasmanian Tigers posted by Helen on September 05, 1998 at 19:44:17:

PK: I think that the evolutionists can speak for themselves on convergent evolution.

PK: The Thylacine looks to me more like a dog from the front and a cat from the rear. When Kurt Wise refers to the Marsupial Tiger, might he be referring to the Tasmanian Tiger? This is another name for the Thylacine.

v/r

Pat

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Posted by Helen on September 05, 1998 at 19:58:06:

Yes, Wise was responding directly to my questions regarding what is alternately called the Tasmanian tiger or the Tasmanian wolf.

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Posted by Deb on September 05, 1998 at 22:09:49:

"Alternately"? I guess it's not so amazingly wolf-like after all, is it...

Deb

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Posted by Helen on September 05, 1998 at 22:59:27:

I guess "wolfness" is in the eye of the beholder! I guess it also depends on which end you are looking at from the outside, and whether or not you are paying more attention to the outside or the skeletal structure.....

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Posted by Pat on September 06, 1998 at 14:05:06:

The gross appearance of these things is certainly "doglike" or catlike, but then the gross appearance of bats is birdlike. It's the details that count. I think we're up against one of those evolution/creation differences that can't be resolved, because there is no "creationist anatomy" yet developed. Again, the discussion on forams suggests to me that we may someday see creationists gain acceptance the way chiropractic is slowly gaining acceptance from physicians. Some physicians, while ignoring the claims that chiropractic can cure cancer, do use practitioners for physical therapy. The key here is to develop a science. I've been putting off Kurt Wise's tape, and I've got to get it. Hopefully, that's what Wise and people like him are working on. As someone else said, if creationists now accept that even new orders can fit within "kinds", there's less and less for us to argue about.

I'm only half joking here. Sorry.

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Posted by Jon on September 05, 1998 at 20:26:46:

In Reply to: Trekking with Tasmanian Tigers posted by Helen on September 05, 1998

Kurt Wise is a very intelligent gentleman, and I'd hate to take him on in his chosen subject -- but evolutionary theory, alas, is clearly not his chosen subject. In point of fact, _superficial_ convergence such as that between the canids and the Tasmanian 'wolf' (which I think looks rather more like a fox) is entirely consistent with evolutionary theory. Similar features for similar tasks. Likewise for _Thylacosmilus_, the 'sabertooth marsupial'.

See, every time we run across convergence of this degree, we also find that the convergence is superficial, and only affects traits that are directly relevant to the organism's chosen niche. If you look a bit deeper, you can always tell convergence from true homologies. Yes, _Thylacosmilus_ has saber-teeth, and in general shape looked remarkably catlike. But _Thylacosmilus_ had a different tooth-count than felids, no retractable claws, a characteristically marsupial skeleton, and huge downward-projecting flanges of bone on the lower jaws that looked like nothing any true cat ever had. _Thylacoleo_, the 'marsupial lion,' had fangs developed from the incisors, not from the canines.

Jon W.

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Posted by Helen on September 05, 1998 at 20:50:10:

I think you folks have a faith in evolution that puts many Christians' faith in God to shame!

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Posted by Pat on September 05, 1998 at 21:10:58:

I have faith in God. Evolution requires facts. And as noted above, the fact that marsupials will evolve to fill niches in the environment is no more surprising than the fact that placentals will do so also. But, as noted, you will always see marsupial characters in marsupial animals. If creation were true, we'd see marsupials and placentals randomly scattered about the globe. But the thylacine had to be a marsupial, because that's all there was to evolve in Tasmania. Finding a placental there would have been pretty hard to understand, given evolution. Convergent evolution, which amazes Kurt Wise as it does, is one more evidence for the history of life.

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Posted by True Seeker on September 05, 1998 at 21:29:18:

Actually Darwin was the first person to come up with a credible explanation in the first place. The explanation is that similar environments can produce similar adaptations. Otherwise, there would be no other way to explain the convergence between members of different groups, like marsupials and placentals.

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Posted by Kevin Kamberg on September 05, 1998 at 21:56:08:

Pat: I have faith in God. Evolution requires facts. And as noted above, the fact that marsupials will evolve to fill niches in the environment is no more surprising than the fact that placentals will do so also. But, as noted,

Why? If, as Jon stated, "we also find that the you will always see marsupial characters in marsupial animals; convergence is superficial, and only affects traits that are directly relevant to the organism's chosen niche" then the difference between being placental and being marsupial have no significant bearing on their respective environments, right? Remembering of course that everything is the direct result of genetics, whether "superficial" or not! If the marsupials evolved from something that was not a marsupial, then what prevents marsupials from evolving into something that is not marsupial???

Your statement, "you will always see marsupial characters in marsupial animals" sounds remarkably like the YEC argument against macroevolution!!! Have you been reading your Bible again? ;-)

If creation were true, we'd see marsupials and placentals randomly scattered about the globe.
Why???

But the thylacine had to be a marsupial, because that's all there was to evolve in Tasmania. Finding a placental there would have been pretty hard to understand, given evolution.

Again, why???

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Posted by Mockingbird1 on September 05, 1998 at 23:59:50:

:PatP: But the thylacine had to be a marsupial, because that's all there was to evolve in Tasmania. Finding a placental there would have been pretty hard to understand, given evolution.

:KK: Again, why??

PK: Until man brought the dog into Australia, the predatory niche was occupied by the mammals present there and they were marsupials. As man spread across the continent, dingoes displaced the marsupial predators. Had the vegetarian maruspials not been subject to predation, they may have all been wiped out by the dingoes. The last place in Australia that man got to was Tasmania. The Aborigines found there were eliminated, and I don't know that they had brought many or any dingoes with them there (ain't it amazing how fresh meat doesn't last so long on voyages ; ). So, the marsupial predators sere still in Tasmania when the Europeans came. The smaller and more robust predator (wolverine/badger like?) survives, the Tasmanian Devil.

v/r

Pat

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Posted by Sumac on September 06, 1998 at 02:29:13:

Kevin K.: If the marsupials evolved from something that was not a marsupial, then what prevents marsupials from evolving into something that is not marsupial???

Nothing. It's just that major transitions such as marsupial to placental mammals are extremely rare. It is much more common for animals (and plants) to just change their external shape to fit their environment.

The Australian continent was isolated from other lands prior to the migration of placental mammals, but not marsupials. I don't know if placental mammals were around yet, but they certainly did not make it there before the split. Since there was no competition from placentals, marsupials were able to evolve to fill all of the niches filled by placentals on the other continents. There are still a few marsupials scattered about (i.e. the opossum in North America), but placentals have been far more successful than marsupials (dare I say "fitter"?). As Mockingbird1 pointed out, the introduction of a placental predator to Australia has not only threatened prey species, but has caused the extinction of marsupial predators that were unable to compete.

It would have been surprising to find an independent line of placentals evolved in Australia, but it is still possible. If it had happened, I'm sure we would have been able to distinguish between Australian placentals and other placentals based on a comparison of morphological and molecular characteristics. What we do see is the more common adaptation to environment.

Similar environments and niches have molded different starting material into similar shapes. The similarities are striking, but, to the trained eye, the differences are just as striking and one must take both into account. So, there may have been dog-like and cat-like marsupials, but the way they became dog-like and cat-like was different than how placental mammals did it.

Perhaps, one day, we will actually witness another transition from marsupial to something else. Perhaps not. Either way, we can still deduce what must have occurred in the past.

> > > > >

Pat: If creation were true, we'd see marsupials and placentals randomly scattered about the globe.

Kevin K: Why???

Why not? Why would all of the marsupials (with the exception of a very few) migrate to Australia and points south after the landing of Noah's Ark? Why wouldn't placentals go there as well? Why wouldn't marsupials populate all of the planet equally? We have clues from geology and paleontology as to why there are so many marsupials concentrated in just a small region of the world. But these clues would not make sense in a Young Earth Creationist scenario.

> > > > >

Pat: But the thylacine had to be a marsupial, because that's all there was to evolve in Tasmania. Finding a placental there would have been pretty hard to understand, given evolution.

Kevin K: Again, why???

See above. Maybe Pat should have said that finding a placental that was not independently evolved would have been pretty hard to understand. I know of no reason to think that another line of placentals could evolve. But again, it would be easily distinguishable from the already established placental line since it would have a different origin.

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Posted by Kevin Kamberg on September 06, 1998 at 15:23:22:

Sumac: The Australian continent was isolated from other lands prior to the migration of placental mammals, but not marsupials.

Is that based on geological dating of the marsupial and placental fossils worldwide, or is it a presumption?

Sumac: It would have been surprising to find an independent line of placentals evolved in Australia, but it is still possible. If it had happened, I'm sure we would have been able to distinguish between Australian placentals and other placentals based on a comparison of morphological and molecular characteristics.

What proposed evolutionary mechanism would prevent indentical convergent evolution in geographically seperated areas?

Pat: If creation were true, we'd see marsupials and placentals randomly scattered about the globe.

Kevin K: Why???

Sumac: Why not? Why would all of the marsupials (with the exception of a very few) migrate to Australia and points south after the landing of Noah's Ark? Why wouldn't placentals go there as well? Why wouldn't marsupials populate all of the planet equally?

I don't know, I wasn't there. But I don't see what part of Creation theory demands that marsupials and placentals disperse equally. Since that is the case, Pat's statement then fails for lack of substantive evidence to support it! It strikes me as an argument from a biased position of personal incredulity! No offense, Pat. :-)

Sumac: Maybe Pat should have said that finding a placental that was not independently evolved would have been pretty hard to understand. I know of no reason to think that another line of placentals could [not] evolve. But again, it would be easily distinguishable from the already established placental line since it would have a different origin.

Again, why? What proposed evolutionary mechanism prevents identical convergent evolution? Why couldn't every single evolutionary mutation that led to felines, for example, not have taken place to end up with an identical convergently evolved species? Assuming the lack of transitional fossils with which to show the different origins, why would the end product have to exhibit evidence of a different origin?

Regards, Kevin

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Posted by Sumac on September 07, 1998 at 01:28:53:

Sumac: The Australian continent was isolated from other lands prior to the migration of placental mammals, but not marsupials.

KK: Is that based on geological dating of the marsupial and placental fossils worldwide, or is it a presumption?

It's based mostly on geological dating and the fossil record. As far as I know, there is a pretty good correlation between the progression of marsupials through South America towards what would have been Australia (as deduced by the fossil record) and the times when the Australian continent split from the Americas (as determined by current measurements of tectonic plate movements). There may be some filling in the gaps as far as the model goes (I am by no means an expert in this field), but it is far from a simple presumption without any facts.

KK: What proposed evolutionary mechanism would prevent identical convergent evolution in geographically separated areas?

It's called "descent with modification". Each lineage has its own history. Similarities can arise through convergent evolution, but there are always tell-tale signs of alternate histories. If a new placental line were to evolve from marsupials today, they would be less divergent from marsupials and, thus, would retain more marsupial characteristics than the already established placental line.

KK: ...I don't see what part of Creation theory demands that marsupials and placentals disperse equally....

There is no reason that they would have to disperse equally. But it seems rather odd that all of the marsupial kinds (assuming that there is more than one marsupial kind) all decided to migrate together to the same corner of the Earth. You would think that at least a few placentals would have migrated with them or that a few marsupials would have gone elsewhere. The fossil record seems to indicate that there was isolation of marsupials due to the separation of the continents (I am not referring to a rapid separation a la Peleg). This isolation was followed by speciation into the various marsupials we see today. Creation "theory" has no explanation for the current distribution of marsupial species. If you want to speculate that there is only one marsupial kind that migrated, then you are going to have to concede evolution to (at least) the family and order levels.

KK: Again, why? What proposed evolutionary mechanism prevents identical convergent evolution? Why couldn't every single evolutionary mutation that led to felines, for example, not have taken place to end up with an identical convergently evolved species? Assuming the lack of transitional fossils with which to show the different origins, why would the end product have to exhibit evidence of a different origin?

Again, see above. Each lineage has a unique history that is evident in both the morphological and biochemical/molecular characteristics of that lineage. Convergent evolution is distinguishable from common ancestry precisely because we can compare and contrast to determine if there was a separate or common history. Sometimes, we can even tell that there was a common history to a point and then there was a divergence to give separate, unique histories. Like I said above, if a new placental line were evolve today, then its history would be unique and distinguishable from the previous placental line.

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Posted by Kevin Kamberg on September 07, 1998 at 04:06:41:

Thanks, Sumac! I'll probably be back with more questions later. For now, it's late and I don't have more than two or three awake brain cells to rub together right now.
In the meantime, I thought you'd enjoy the link at the bottom. ;-)

Regards, Kevin

http://www.newscientist.com/ns/971129/nmammals.html

HOME · NEW SCIENTIST · NS+

[Archive: 29 November 1997]

Uprooting our family tree

By Ian Anderson, Melbourne

A tiny fossil jawbone, unearthed on an Australian beach, could turn our picture of mammalian evolution upside down. The fossil's discoverers claim it is 115 million years old and comes from a shrew-like placental mammal. Yet nothing of the sort is supposed to have existed in Australia until 5 million years ago.  Most modern mammals--including ourselves--are placentals, in which the developing young are nurtured inside the uterus. They are believed to have originated in the northern hemisphere more than 100 million years ago and then slowly spread throughout the globe.

The other two mammalian groups, the egg-laying monotremes and the marsupials, in which the young mature in a pouch, struggled to compete with the advancing placentals. Australia, into which the first terrestrial placentals were thought to have migrated only 5 million years ago, is their main remaining stronghold.  At least, that is the established view. But the new find suggests that placentals arose simultaneously in both the southern and northern hemispheres. If so, the textbooks must be rewritten. "To find a placental mammal in Australia that ancient fits nothing we know," says David Archibald of San Diego State University.  The jaw was discovered in March near Inverloch, about 150 kilometres southeast of Melbourne, by Nicola Barton, a volunteer from London working on a dig organised by Tom Rich of the Museum of Victoria in Melbourne and his wife, Pat Vickers-Rich of Monash University in Melbourne.

Rich, Vickers-Rich and their colleagues describe the jaw, from an animal they have named Ausktribosphenos nyktos, in Science (vol 278, p. 1438). They believe A. nyktos was an insectivore that lived on the landmass of Gondwana that later split up into Australia, South America, southern Africa and Antarctica. Its home then lay at a latitude of about 70° south--cold and plunged into darkness for three months of the year.
The bone is 16 millimetres long with teeth less than 1·8 millimetres high that are adapted for slicing and crushing food--a feature not found in monotremes.  The jaw has three molars and five premolars, which is typical of placentals. Marsupials usually have four molars and three premolars.  One premolar also seems to be a hybrid between a simple, triangular premolar and a more complex molar. This pattern is found in placentals, but not in marsupials. "On the way we recognise placentals in 1997, this thing fits the bill," says Rich.  But some palaeontologists are not convinced. The main objection is the structure of the talonid basin, a depression at the back of each molar. In placentals this is a single structure, but in A. nyktos it is divided into two. "The talonid basin is unlike anything you would expect of a primitive placental mammal," says Alfred Crompton of Harvard University.

"Frankly, I think it is something new--not a monotreme, not a placental and not a marsupial," says William Clemens of the University of California at Berkeley. "It's a new group that was either converging with other mammals or running parallel with them, eventually dying out."   Rich maintains that similar doubts could be raised about several fossils from the northern hemisphere that are generally assumed to be primitive placentals.

"We can't assume it is not a placental because we know so little about the evolutionary history of mammals on Gondwana," agrees David Krause of the State University of New York in Stony Brook.

This ignorance will now have to be addressed, Rich argues. Whether or not A. nyktos proves to be a placental, he says, its discovery means palaeontologists must give more thought to the importance of the southern hemisphere in mammalian evolution.

From New Scientist, 29 November 1997

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Posted by Mockingbird1 on September 06, 1998 at 00:04:40:

PK: Hey Pat!

PatP: If creation were true, we'd see marsupials and placentals randomly scattered about the globe.

PK: If I found a Marsupial in the other side of the world from Tasmania, I wouldn't call it 'proof' of creation. We just call it possum. That bone structure is different in some areas between placentals and marsupials should be unsurprising; if they were the indistinguishable, we wouldn't distinguish the marsupials from the placentals.

v/r

Pat

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Posted by SeeJay on September 06, 1998 at 09:56:19:

In Reply to: Trekking with Tasmanian Tigers posted by Helen on September 05, 1998 at 19:44:17:

I have seen footage of the Thylacine... a poor caged beast filmed earlier this century.

It had a curious lope and head posture, which one could not confuse with either dog or cat. I was reminded much more strongly of a kangaroo, in particular by the development of the hind legs. Fold a kangaroo over and give him a larger head and torso, stronger forelegs and a smaller tail and, viola, a Tasmanian Tiger.

As I live in the land of Auz I speak from experience.

SeeJay

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Posted by Mockingbird1 on September 06, 1998 at 19:13:10:

PK: Goodonyamate, from upover!

PK: Two things about 'roos 1) they really don't like to be petted about the neck (really!). 2) They don't have such large canine teeth as the Thalycine, at least not from what I could see playing with them in the zoo outside Adelaide.

PK: From the seemingly instinctive reaction on the neck touching, I infer that they have been subject to predation far longer than dingoes have been in Oz and have a well developed response to possible threats. I really don't think the Thylacine evolved to their final form from a herbivorous form such as the roo, more likely from an omnivorous form or from a previous carnivorous form.

v/r

Pat

 

 

 

 
 
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