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Author Topic:   Is convergent evolution evidence against common descent?
mark24
Member (Idle past 5185 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 226 of 311 (215567)
06-09-2005 4:34 AM
Reply to: Message 222 by randman
06-09-2005 12:32 AM


Re: Inconsistent?
randman,
I think you need to read those articles you linked to more carefully. Note the following.
Perhaps you should read it & take a look at the cladogram again, & take what I am posting in context. All that has occurred is, is that hippopotamids have been nested adjacent to the cetacea rather than the suiformes. Once again you are looking at incongruences at the expense of the congruences. There is no particular reason why cetacean "insertions of short and long interpersed elements" have anything to do with two-toed ungulates. What particularly about the marine environment "pushes" whales & artiodactyls together?
Morphological data places cetaceans within the artiodactlya, & so do different molecular data sets. You have seen the odds of against congruent cladograms, why did you ignore the very point being made?Because you are incapable of addressing the congruent nature of phylogenetics/cladistics, clearly. All you have done is ignore the massive overall pattern & try to fish for errors.
Again, I stress the statistical nature of the evidence.
But regardless, what we are talking here are assumptions. Are the assumptions with which
we view the data correct?
The assumptions are being tested all the time with the congruent nature of the data.
Your comments on ID are completely and wholly wrong. We can test for design (forensics), irreducible complexity (stats), and ID mechanisms (quantum field research).
Utterly, utterly false. IC doesn't = inevolveable, therefore isn't a test of it. What is "intelligent" about quantum mechanics? Nothing at all.
Wrong again unless I am misreading you. Larger and different data sets have emerged and produced in remarkable similarity. The Marsupial and Placental pairs are conclusive evidence of that, unless you think they did not evolve convergently.
Again you ignore the wider evidence. If marsupials/placentals were so convergent, we wouldn't be able to tell them apart. But we can do so so, & do so easily, No denying that convergent evolution exists, but that it totally masks other data is clearly falsified by the fact we recognise marsupials & placentals in the first place. Remember the cladogram that Ned predicted? Nor can marsupials be anatomically identified just by their reproductive strategy, they can be recognised by other anatomical features.
Convergent DNA means that there is some predisposition within the DNA that offers sequences and mutations more than by random chance.
But there is no reason that an Iguana's DNA & morphology is guided to look like being ancestral to birds. Or multiple sequences & morphology in cetaceans as nesting them within the artiodactyla.
You are always banging on about the assumptions of others being flawed, & yet your assumption regarding congruent cladograms is entirely unwarranted.
It is therefore likely that it provides some sort of guiding factor in producing similarities, especially the predispositions that are naturally selected for.
It is not "likely". It is another entirely unwarranted assumption.
In truth, the mere fact of convergent DNA suggests the way things are set up is somewhat determinative, and certainly not random.
Which is falsified by the fact that sequences are not identical, nor do they appear to be working towards some ideal, but are evidently divergent in the majority of cases. Genetic studies in the lab testify to this. Phylogenetic studies on AIDS & bacterial genomes have successfully returned known phylogenies that are divergent by nature, not convergent. Your "convergent" DNA problem is conspicuously absent. Surely bacterial populations separated, but under the same conditions in a petri dish shouldn't exhibit divergence? Surely HIV, the common cold, etc. shouldn't be diverging when their DNA is "predisposed" towards a particular sequence?
The pattern of descent can be reliably inferred in these cases, & this pattern is crashingly evident wherever we look.
Convergency is evidently a minor problem.
Mark
This message has been edited by mark24, 06-09-2005 08:11 AM

There are 10 kinds of people in this world; those that understand binary, & those that don't

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Replies to this message:
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sfs
Member (Idle past 2524 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 227 of 311 (215570)
06-09-2005 6:41 AM
Reply to: Message 215 by mark24
06-08-2005 4:44 PM


Re: Inconsistent?
quote:
Anyway, the number of taxa in the trees is eight, & the number of possible outcomes for an eight taxa rooted tree is 135,135. Given we have just got two trees exactly the same, the odds of that occurring is 135,135^2 = 18,261,468,225 : 1
The odds that two random 8-taxa trees will match are 135,135:1. That is, the first tree can be anything; you get a match if the second tree happens to be identical to the first, which is true for one out of the 135,135 possible trees.

This message is a reply to:
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mark24
Member (Idle past 5185 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 228 of 311 (215574)
06-09-2005 7:51 AM
Reply to: Message 227 by sfs
06-09-2005 6:41 AM


Re: Inconsistent?
sfs, oop, you are correct, I forgot to add that the two are consistent with the morphology tree. I'll head back & edit.
Cheers,
Mark

There are 10 kinds of people in this world; those that understand binary, & those that don't

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randman 
Suspended Member (Idle past 4889 days)
Posts: 6367
Joined: 05-26-2005


Message 229 of 311 (215584)
06-09-2005 9:19 AM
Reply to: Message 226 by mark24
06-09-2005 4:34 AM


Re: Inconsistent?
Mark, you are dodging the point. Just look at the Marsupial and Placental pairs. They can easily tell them apart due to the pouch vs placental thing. Without that, it would be a problem. Your post just seems to want to minimize what you guys claim convergency can produce.
Take the 3 ear bones. If convergency can produce identical ear design in the sense of the 3 ear bones, it could darn well explain anything, and that's something you don't want to admit.
Nor are you admitting the real fact, as is plain in the literature, that molecular research is and has caused a rethinking of classifications from where strictly fossil-based classification would place the creatures.
You just ignore that and insist on the ole, you can't see the forest for the trees. Well, if you can't honestly admit that molecular research has caused a rethinking of parts of how evolution occurred, and you have to pretend convergent evolution displays more limits than the evidence shows, despite basic things like the ear and eye repeatedly showing up independently, then I have to wonder why?
Same with convegent DNA. In typical fashion for evolutionist proponents, rather than admit what cannot be denied as a fact, you want to deny every fact that you fear could be used against common descent theory, and overstate your case. No one denied, not even YEC, that divergency occurs. That's not the point. The point is we have discovered convergency tendencies in DNA.
Btw, I wonder what the odds are for the process of evolution to independently produce the same feature, over and over again.
This message has been edited by randman, 06-09-2005 09:23 AM

This message is a reply to:
 Message 226 by mark24, posted 06-09-2005 4:34 AM mark24 has replied

Replies to this message:
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wj
Inactive Member


Message 230 of 311 (215585)
06-09-2005 9:23 AM
Reply to: Message 221 by randman
06-09-2005 12:11 AM


Re: Fun with phylogenies
Randman, do you understand the implications of Wounded King's analysis in message #216?
Sequence type explicitly set to Protein
Sequence format is Pearson
Sequence 1: Wombat 381 aa
Sequence 2: Dunnart 381 aa
Sequence 3: Mouse 381 aa
Sequence 4: Woodchuck 379 aa
Sequence 5: Thylacine 381 aa
Sequence 6: Wolf 379 aa
Start of Pairwise alignments
Aligning...
Sequences (5:6) Aligned. Score: 80
Sequences (1:2) Aligned. Score: 87
Sequences (3:4) Aligned. Score: 84
Sequences (2:3) Aligned. Score: 80
Sequences (4:5) Aligned. Score: 80
Sequences (1:3) Aligned. Score: 80
Sequences (3:5) Aligned. Score: 79
Sequences (2:4) Aligned. Score: 81
Sequences (4:6) Aligned. Score: 87
Sequences (1:4) Aligned. Score: 79
Sequences (3:6) Aligned. Score: 86
Sequences (2:5) Aligned. Score: 92
Sequences (1:5) Aligned. Score: 87
Sequences (2:6) Aligned. Score: 81
Sequences (1:6) Aligned. Score: 80
I can't copy the tree so go back and look at it again.
The marsupials cluster together; the placentals cluster together. The placental wolf and marsupial thylacine show less genetic similarities to eachother than to the other members of their own suborder. The marsupial durrant and placental mouse are as genetically far apart as any pair in that sample despite some external similarities.
Your musing " It will be interesting to see, eventually, if similar physical appearance does related to similar genetic sequences or not" has already been done before your very eyes and demonstrated that there is not necessarily a relation between physical appearances and genetic sequences. Did you completly miss the point of the exercise?

This message is a reply to:
 Message 221 by randman, posted 06-09-2005 12:11 AM randman has replied

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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 231 of 311 (215590)
06-09-2005 9:37 AM
Reply to: Message 229 by randman
06-09-2005 9:19 AM


Re: Inconsistent?
Well let us look at another strand of evidence.
What about the early development of the Dunnart in comparison to placental rodents.
Early development of the neural plate, neural crest and facial region of marsupials.
Smith KK.
J Anat. 2001 Jul-Aug;199(Pt 1-2):121-31.
Marsupial mammals have a distinctive reproductive strategy. The young are born after an exceptionally short period of organogenesis and are consequently extremely altricial. Yet because they must be functionally independent in an essentially embryonic condition, the marsupial neonate exhibits a unique suite of adaptations. In particular, certain bones of the facial region, most cranial musculature and a few additional structures are accelerated in their development. In contrast, central nervous system structures, especially the forebrain, are markedly premature at birth, resembling an embryonic d 11 or 12 mouse. This review examines the developmental processes that are modified to produce these evolutionary changes. The focus is on the early development of the neural plate, neural crest and facial region in the marsupial, Monodelphis domestica, compared with patterns reported for rodents. Neural crest begins differentiation and migration at the neural plate stage, which results in large accumulations of neural crest in the facial region at an early stage of development. The early accumulation of neural crest provides the material for the accelerated development of oral and facial structures. The first arch region is massive in the early embryo, and the development of the olfactory placode and frontonasal region is advanced relative to the forebrain region. The development of the forebrain is delayed in marsupials relative to the hindbrain or facial region. These observations illustrate how development may be modified to produce evolutionary changes that distinguish taxa. Further, they suggest that development is not necessarily highly conserved, but instead may be quite plastic.
So there are a number of significant differences in the developmental programs of the marsupial and placental rodent like species.
TTFN,
WK

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randman 
Suspended Member (Idle past 4889 days)
Posts: 6367
Joined: 05-26-2005


Message 232 of 311 (215593)
06-09-2005 9:38 AM
Reply to: Message 230 by wj
06-09-2005 9:23 AM


Re: Fun with phylogenies
Obviously, based on my comments I saw that.
Do you realize that by showing that you raise a problematic issue for common descent analysis where you do not have DNA?
Obviously not, it seems.
Take the reptile/mammal theorized evolution. Someone parades morphological similarities, often of the jaw, and says, look, this had to be common descent in action.
No, now we know it could be convergent evolution that is producing the similar forms. I wonder what else it "could be" if we admitted to the totality of the evidence instead of trying to cram everything into one mechanism.
Right now, based on very limited research, we see a tendency for similar forms to arise from remarkably dis-similar DNA, right?
Of course, as WK pointed out, and you fail to have noted, we don't have access or it isn't there yet, to the research that could really verify it. Running a few protein sequences through a program is not exactly earth-shattering that it is congruent with current concepts since they would have already adjusted the trees if this data did not fit.
What I wondered if we did not find some anomalies. We haven't seen that yet, but judging how some here want to avoid any data that is problematic and pretend it isn't the case, it's not like you guys are looking for potential holes in the case, posting, etc,...which is what you ought to be looking for instead of running a few through and proclaiming somehow this makes your case.
By doing so, you fail to see the larger point. If convergent evolution is that strong, you cannot necessasrily tell without DNA if similar fossils indicate common ancestry, even if you assume common descent overall.
Besides that, one then has to wonder about other common factors that could be involved.
Judging by the statistically unlikeliness of nature repeatedly reinventing the wheel, eyes, ears, etc,...., the logical inference should be there appears to be a design embedded into the physical properities of the universe.

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Replies to this message:
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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 233 of 311 (215594)
06-09-2005 9:44 AM
Reply to: Message 230 by wj
06-09-2005 9:23 AM


Re: Fun with phylogenies
Your musing " It will be interesting to see, eventually, if similar physical appearance does related to similar genetic sequences or not" has already been done before your very eyes and demonstrated that there is not necessarily a relation between physical appearances and genetic sequences. Did you completly miss the point of the exercise?
This isn't really true. The sequences we analysed were for Cytochrome B, a mitochondrial gene regularly used for phylogenetic studies, and in the othe cases the Beta chain of Hemoglobin. Neither of these is likely to have any relevance to the gross anatomy of the organisms. Until we have the relevant genes/proteins which control the development of the similar anatomical features thought to have evolved independently, we can't say whether they show the same genetic patterns as the Cytochrome and Hemoglobin proteins.
TTFN,
WK

This message is a reply to:
 Message 230 by wj, posted 06-09-2005 9:23 AM wj has not replied

Modulous
Member
Posts: 7799
From: Manchester, UK
Joined: 05-01-2005


Message 234 of 311 (215604)
06-09-2005 11:02 AM
Reply to: Message 232 by randman
06-09-2005 9:38 AM


Re: Fun with phylogenies
Take the reptile/mammal theorized evolution. Someone parades morphological similarities, often of the jaw, and says, look, this had to be common descent in action.
No, now we know it could be convergent evolution that is producing the similar forms. I wonder what else it "could be" if we admitted to the totality of the evidence instead of trying to cram everything into one mechanism.
Yes, it *could* be convergent evolution...but the fossil record seems to tell a different story. Mammals could not converge to reptilian features, until mammals existed...where did they seem to come from? They arrived on the scene when reptillian creatures dominated the land. Thus it is theorized they evolved from the reptillian creatures, rather than converged to them (that is to say, there is no evidence of convergence and there is evidence of common ancestry).
...but judging how some here want to avoid any data that is problematic and pretend it isn't the case, it's not like you guys are looking for potential holes in the case, posting, etc,...which is what you ought to be looking for instead of running a few through and proclaiming somehow this makes your case.
The 'some' you are referring to must be in the minority. Everyone I have seen writing here seems to be discussing the anomolies quite straightforwardly.
Judging by the statistically unlikeliness of nature repeatedly reinventing the wheel, eyes, ears, etc,...., the logical inference should be there appears to be a design embedded into the physical properities of the universe.
Its not really a logical inference. We don't know the statistic likelihood of eyes evolving from seperate sources without an arch-designer. Evolution is happy that nature would do this, since vision is a massive advantage to an organism. That eyes end up with similar function is entirely to be expected.
The logical inference then, is that nature reinvents things because it is a blind process, but is working from largely the same parameters (pretty much the same things are being selected for and against in the evolution of an eye).

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Replies to this message:
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Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 235 of 311 (215618)
06-09-2005 11:41 AM


Genomic data on a marsupial
Ask and ye shall receive.
There is some early draft genome data on a marsupial, in the case the gray short-tailed opposum, available at Ensembl.
All we need to do now is for Randman to decide what he thinks would be a good placental homologue, ideally another organism in the Ensembl database with a finished or partially finished genome.
If none of these seem suitable then it might still be possible to find another organism for whom some genes likely to be relevant have been sequenced.
TTFN,
WK
P.S. If you like Randman we could do the actual bioinformatic side of this on Ned's spin off thread, and if we find anything interesting we can always report back here.

Replies to this message:
 Message 292 by randman, posted 06-11-2005 3:49 AM Wounded King has replied

mark24
Member (Idle past 5185 days)
Posts: 3857
From: UK
Joined: 12-01-2001


Message 236 of 311 (215644)
06-09-2005 12:53 PM
Reply to: Message 229 by randman
06-09-2005 9:19 AM


Re: Inconsistent?
randman,
Mark, you are dodging the point. Just look at the Marsupial and Placental pairs. They can easily tell them apart due to the pouch vs placental thing. Without that, it would be a problem.
Palaeontologists manage to tell them apart without pouches & plantenta by just the fossil bones, which was my point.
Try again...
quote:
If marsupials/placentals were so convergent, we wouldn't be able to tell them apart. But we can do so, & do so easily, No denying that convergent evolution exists, but that it totally masks other data is clearly falsified by the fact we recognise marsupials & placentals in the first place. Remember the cladogram that Ned predicted? Nor can marsupials be anatomically identified just by their reproductive strategy, they can be recognised by other anatomical features.
  —mark
Your post just seems to want to minimize what you guys claim convergency can produce. Take the 3 ear bones. If convergency can produce identical ear design in the sense of the 3 ear bones, it could darn well explain anything, and that's something you don't want to admit.
What do you mean by this? The 3 bones you mention were in place before placentals, marsupials, & monotremes diverged. What makes you think it was convergence?
Nor are you admitting the real fact, as is plain in the literature, that molecular research is and has caused a rethinking of classifications from where strictly fossil-based classification would place the creatures.
I am admitting it, & more power to its collective elbow, but it's neither here nor there to the conclusion of common decsent. The shift in the placement of cetacea within the artiodactyls is a perfect example of this. You seem to want this to mean that cladistics should be binned, whilst totally ignoring the fact the data taken as a whole is congruent in a way that overwhelmingly supports descent.I acknowledge & accept all the data, you look at the incongruence & ignore the larger congruence.
This is worth repeating. My great-grandmother smoked like a trooper all her life & lived to the age of 93. Given that this is an above average age, I therefore conclude that smoking is good for you. This is exactly what you are doing by focussing on the examples that you want to see, & ignoring the rest. My view takes in the data as a whole & as a result I am able to see the signal through the noise.
I have provided an example of congruency that is 135,135:1 against. In order to render this statistically insignificant, you are required to provide 135,135 cladogram pairs that have zero congruence, such is the nature of corroborative evidence. I won't hold my breath.
and you have to pretend convergent evolution displays more limits than the evidence shows
You have to show that it does place significant limits, which you haven't done. The burden of proof is on the claimant. The evidence that it doesn't is in the congruence of unrelated data sets.
Same with convegent DNA. In typical fashion for evolutionist proponents, rather than admit what cannot be denied as a fact, you want to deny every fact that you fear could be used against common descent theory, and overstate your case. No one denied, not even YEC, that divergency occurs. That's not the point. The point is we have discovered convergency tendencies in DNA.
I overstate my case? Says the person who gets evidence of non-random mutations & makes all sorts of unwarranted extrapolations about the frequency & effects of such a phenomenon on congruency, & wild claims of determinacy.
It is incumbent on you to show convergence is so prevalent at all levels that it renders cladistics moot as a tool for inferring descent. It is incumbent on you to show why multiple, independent sequences & morphology are an expectation of convergence.
For example, whales are most similar morphologically & genetically to artiodactyls. Why doesn't one genetic study point to a whale fish affinity? Another canines, another ursids, another sharks? Seals, & sealions, anyone? Surely the environment that a whale finds itself under should force similarities with organisms sharing similar niches in order to force convergence? But whales don't, the evidence consistently points to an artiodactyl ancestry, not a shark ancestry, not a sealion ancestry, not a canine ancestry, not a primate ancestry, an artiodactyl ancestry.
There is no reason why any genes phylogeny should be congruent with any other genes phylogeny, nor any "metabolic" gene sequence with morphology.
I have admitted divergency occurs, I simply deny that it occurs as much as you would like. The evidence of this is that descents prediction of congruent phylogenies is borne out, & this is not consistent with convergence, convergence would ruin it, which is rather your point, after all. Also, I have pointed out to you known phylogenies exist where divergence, rather than convergence is the norm. If convergency was prevalent, large marine animals like whales, sealions etc would show convergence beyond obvious adaptations to their environment. They would be more similar heamaglobin-wise, cytochrome c-wise, NADH-wise, morphology-wise, etc. But they are NOT. They show affinities with very different clades that exist in totally different environments.
Sequence & morphology based cladograms cannot be explained by convergence. The only explanation that explains the data is common descent.
Mark
ps Might I suggest you start smoking 40 cigarettes a day, it will result in a longer lifespan. The evidence clearly supports this conclusion.
This message has been edited by mark24, 06-09-2005 05:58 PM

There are 10 kinds of people in this world; those that understand binary, & those that don't

This message is a reply to:
 Message 229 by randman, posted 06-09-2005 9:19 AM randman has replied

Replies to this message:
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MangyTiger
Member (Idle past 6344 days)
Posts: 989
From: Leicester, UK
Joined: 07-30-2004


Message 237 of 311 (215678)
06-09-2005 3:35 PM
Reply to: Message 230 by wj
06-09-2005 9:23 AM


Re: Fun with phylogenies
I can't copy the tree so go back and look at it again.
The marsupials cluster together; the placentals cluster together. The placental wolf and marsupial thylacine show less genetic similarities to eachother than to the other members of their own suborder. The marsupial durrant and placental mouse are as genetically far apart as any pair in that sample despite some external similarities.
I think a reasonable way of showing this when you can't post the tree is to sort the alignments score in descending order. In this example you can clearly see the three groupings - the marsupials with each other, the placentals with other and finally the marsupial and placental combinations at the bottom (exactly as everybody but randman would predict )
Sequences (2:5) Aligned. Score: 92 (Dunnart:Thylacine)
Sequences (1:5) Aligned. Score: 87 (Wombat:Thylacine)
Sequences (1:2) Aligned. Score: 87 (Wombat: Dunnart) unnart isn't a good thing to have in the text!
Sequences (4:6) Aligned. Score: 87 (Woodchuck:Wolf)
Sequences (3:6) Aligned. Score: 86 (Mouse:Wolf)
Sequences (3:4) Aligned. Score: 84 (Mouse:Woodchuck)
Sequences (2:4) Aligned. Score: 81 (Dunnart:Woodchuck)
Sequences (2:6) Aligned. Score: 81 (Dunnart:Wolf)
Sequences (1:6) Aligned. Score: 80 (Wombat:Wolf)
Sequences (5:6) Aligned. Score: 80 (Thylacine:Wolf)
Sequences (2:3) Aligned. Score: 80 (Dunnart:Mouse)
Sequences (4:5) Aligned. Score: 80 (Woodchuck:Thylacine)
Sequences (1:3) Aligned. Score: 80 (Wombat:Mouse)
Sequences (3:5) Aligned. Score: 79 (Mouse:Thylacine)
Sequences (1:4) Aligned. Score: 79 (Wombat:Woodchuck)

Oops! Wrong Planet

This message is a reply to:
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NosyNed
Member
Posts: 8996
From: Canada
Joined: 04-04-2003


Message 238 of 311 (215681)
06-09-2005 3:48 PM
Reply to: Message 234 by Modulous
06-09-2005 11:02 AM


Reptiles and Mammals
Yes, it *could* be convergent evolution...but the fossil record seems to tell a different story. Mammals could not converge to reptilian features, until mammals existed...where did they seem to come from? They arrived on the scene when reptillian creatures dominated the land. Thus it is theorized they evolved from the reptillian creatures, rather than converged to them (that is to say, there is no evidence of convergence and there is evidence of common ancestry).
But dolphins converged on icthyosaurs long after there were no ichtyhosaurs. I don't think the above shows that Mammals didn't converger on reptiles.
What does show that is the descent and not convergence is the sequence of fossils linking mammals back to reptiles. This argues against randman's idea.

This message is a reply to:
 Message 234 by Modulous, posted 06-09-2005 11:02 AM Modulous has replied

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MangyTiger
Member (Idle past 6344 days)
Posts: 989
From: Leicester, UK
Joined: 07-30-2004


Message 239 of 311 (215683)
06-09-2005 3:49 PM
Reply to: Message 229 by randman
06-09-2005 9:19 AM


Re: Inconsistent?
Mark, you are dodging the point. Just look at the Marsupial and Placental pairs. They can easily tell them apart due to the pouch vs placental thing. Without that, it would be a problem. Your post just seems to want to minimize what you guys claim convergency can produce.
I think you're very wrong about this. The following is from Animal Diversity Web:
Marsupials differ from placentals in a number of important and obvious ways. The palate of marsupials is usually "fenestrated," that is, it contains large gaps or spaces in its bony surface. The angular process of the dentary is inflected (bent) medially in almost all marsupials. The braincase is small and narrow. It houses a relatively small and simple brain compared to that of similar-sized placentals. The jugal is large, extending posteriorally so that it actually contacts and forms part of the glenoid fossa. The lacrimal canal is slightly anterior to the orbit so that it opens on the surface of the face rather than inside the orbital space. The bullae are sometimes not ossified, and when they are, they are formed largely by extensions from the alisphenoid.
Tooth form varies considerably among species of marsupials, but an easy and reliable character for recognizing members of the group is that the number of incisors in the upper jaw is different from the number in the lower (except in one family, the Vombatidae). The number is equal in most (but not all!) placentals. Also, the maximum number of incisors (seen in several families) is 5/4, in contrast to 3/3 in placentals. The number of premolars and molars also differs between the groups (3/3 4/4 in marsupials, 4/4 3/3 in placentals), and the pattern of tooth replacement (milk teeth by adult teeth) differs, but these traits are difficult to use to recognize specimens.
The postcranial skeletons of marsupials differ from those of placentals (but resemble monotremes) in that modern marsupials have epipubic bones in the body wall, projecting anteriorally from the pelvis (epipubics are vestigial in recently extinct thylacines and were absent in at least one extinct group).
Myers, P. 2000. "Metatheria" (On-line), Animal Diversity Web. Accessed June 09, 2005 at ADW: Metatheria: INFORMATION.

Oops! Wrong Planet

This message is a reply to:
 Message 229 by randman, posted 06-09-2005 9:19 AM randman has replied

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Modulous
Member
Posts: 7799
From: Manchester, UK
Joined: 05-01-2005


Message 240 of 311 (215685)
06-09-2005 3:56 PM
Reply to: Message 238 by NosyNed
06-09-2005 3:48 PM


Re: Reptiles and Mammals
What does show that is the descent and not convergence is the sequence of fossils linking mammals back to reptiles.
Agreed, I'm saying pretty much the same thing:
quote:
...but the fossil record seems to tell a different story.
But dolphins converged on icthyosaurs long after there were no ichtyhosaurs.
True, but dolphins didn't converge until after dolphin-like creatures existed to do the converging. Which is what I was saying:
quote:
Mammals could not converge to reptilian features, until mammals existed

This message is a reply to:
 Message 238 by NosyNed, posted 06-09-2005 3:48 PM NosyNed has not replied

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