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The opening definitions are very confusing and appear to be confusing/confounding cladistics with phylogenetics, among other things.
Definition #1- Cladistics is not "the science of phylogenetics." This sentence has two problems. First, cladistics is a starting point method for figuring out a phylogeny. It is not the actual making a phylogeny, several of which could come from one cladistic analysis (see Cladograms and Phylogenetic Trees, Wiley EO, Systematic Zoology, 1979). Second, and in a similar vein, it is not "the" method as in the only one for figuring out a phylogeny (again, it doesn't even figure them out in the first place it is only a starting point). Third, and MOST importantly, this definition really doesn't tell the reader anything about cladistics. It just tells the reader that it is "a method", but never actually describes the method (in fact no where in the article is this so called "method of cladistics" ever defined or described, not even telling the reading what a shared derived characteristic is). Therefore I wanted to replace the opening definition with: "A method for establishing the relationships of various individuals, items, concepts, etc through the use of shared characteristics." This definition is backed up with the following citations:
"Cladistics: Theory and Practice of Parsimony Analysis" page 1: "Cladistics is a method of classification that groups taxa hierarchically into sets and subsets." page 2: "The aim of cladistics is to establish sister-group relationships, and the concept of two taxa being more closely related than either is to a third." "Sister groups are hypothesized through the analysis of characters"
"Transformed Cladistics, Taxonomy and Evolution" page 68: "On the basis of a comparison of organisms, perceived similarities are utilized to choose those characters that will be used for more detailed comparisons leading to the construction of a cladogram. Central to this endeavor is the recognition of shared derived characters."
UCMP University Of California Museum of Paleontology Website on cladistics: "Cladistics is a particular method of hypothesizing relationships among organisms." "The basic idea behind cladistics is that members of a group share a common evolutionary history, and are "closely related," more so to members of the same group than to other organisms. These groups are recognized by sharing unique features which were not present in distant ancestors."
Definition #2- This is confusing due to its wording. Its original form leaves it unclear if the words "phylogenetic systematics" are included because they are somehow a synonym for cladistics (if so why is that down here in definitions) or whether it is a whole different field and hence no longer a definition of the main heading word of the page. I tried to emphasize that the second definition is a narrower form of the first definition and that it goes by a specific name (phylogenetic systematics). Hence my definition: "phylogenetic systematics, is a narrower and more formal version of the above which uses the principle of only naming clades as its source of information for taxonomy. This is sometimes pejoratively called "cladism."" — Preceding unsigned comment added by Nathank2 ( talk • contribs) 21:21, 29 October 2012 (UTC)
Nathank2 ( talk) 00:06, 30 October 2012 (UTC)
Looking back over the old revisions of this article, things seem to have been clearer before. The very old version from [ 09:22, 6 June 2003] is almost exactly what I am suggesting. It's clear and understandable for a lay person. Version [ 20:23, 19 January 2007] is a little more convoluted and difficult to understand at the beginning, but the entirety of the opening section is very good and does a good job of giving a basic explanation of the whole concept. Nathank2 ( talk) 16:14, 30 October 2012 (UTC)
Nathank2 ( talk) 21:11, 30 October 2012 (UTC)
Hello, I need a help from people with knowledge in systematics and taxonomy to discuss the Template:SysTax. This template was removed from the pages where it appears for discussion and improvment. Thanks Zorahia ( talk) 15:22, 22 March 2013 (UTC)
RE: Maas, Philipp (2010), "Text Genealogy, Textual Criticism and Editorial Technique", in Jürgen, Hanneder; Maas, Philipp, Wiener Zeitschrift für die Kunde Südasiens (Vienna: Austrian Academy of Sciences), 52-53: 63–120, doi:10.1553/wzks2009-2010s63
The article title is wrong. At pages 63-120 of this volume, Maas's article title is "Computer Aided Stemmatics — The Case of Fifty-Two Text Versions of Carakasaṃhitā Vimānasthāna 8.67-157."
The title given to this issue of the journal, which Maas CO-edited, is indeed Text Genealogy, Textual Criticism and Editorial Technique. But in the references, that title for the journal is given as the title for the article. It is unclear what is being cited. — Preceding unsigned comment added by 50.133.222.248 ( talk) 05:15, 19 May 2013 (UTC)
Peter Brown deleted my edits to the cladistic pages here, suggesting that they gave too much credit to Steve Farris. I see that he is not a systematist, and I wonder just how he justifies his editorial choices, given that the section called for greater detail, which I provided. Is he suggesting that the historical information I provided is not true? - Andy Brower — Preceding unsigned comment added by Abrower ( talk • contribs) 13:00, 20 May 2013 (UTC)
See here. A similar example, which thankfully hasn't escalated to an edit-war due to the timely intervention-edit of another user, can be found here. From my point of view, this is something trivial... Thanatos| talk 19:59, 24 May 2013 (UTC)
The first sentence of the page currently has two citations for the parenthetical statement that the word "cladistics" derives from Greek κλάδος, klados, i.e. "branch". I see the first one as spurious ( "cladistics". Online Etymology Dictionary.) because it says nothing about this, but the editor who inserted it has repeatedly reverted me. Could someone else please look at this matter? Thanks. Sminthopsis84 ( talk) 20:01, 24 May 2013 (UTC)
What is the difference (if any) between cladistics and classic biological taxonomy? How do they relate to one another? What was there before cladistics was invented? Or is cladistics just a new name for an old discipline? The article on "Taxonomy (biology)" mentions "cladistic" only in passing, without any explanation of its role. — Preceding unsigned comment added by 213.207.170.238 ( talk) 07:49, 29 July 2013 (UTC)
In Cladistics#Terminology for taxa is the statement:
Is saying that the character states were "inherited by its descendants (unless secondarily lost)" just a fancy way of saying that the states were inherited by its descendants unless they weren't? If so, the phrase is vacuous and could be omitted. Peter Brown ( talk) 02:12, 2 August 2013 (UTC)
A clade is characterized by one or more apomorphies: derived character states inferred to have been present in the first member of the taxon and not inherited by any other taxa.This isn't right, because it doesn't say that the apomorphies were inherited by that taxon, only that they weren't inherited by any other. If you omit the parenthesised part, you get
A clade is characterized by one or more apomorphies: derived character states inferred to have been present in the first member of the taxon, inherited by its descendants, and not inherited by any other taxa.Since bare plurals in English often logically mean "all", this can be misread as
... inherited by all its descendants ..., so the qualification is needed to avoid this interpretation. A fuller statement might be something like
A clade is characterized by one or more apomorphies: derived character states inferred to have been present in the first member of the taxon, present through inheritance in most of its descendants (but not necessarily all since they may have lost it), and not inherited by any other taxa.Peter coxhead ( talk) 09:14, 2 August 2013 (UTC)
was secondarily lost" is just a misleading way of saying "was not inherited– well, this is at the heart of our disagreement. Clearly "was lost" is just a way of saying "was not inherited". However, the addition of "secondarily" here is an attempt to say more, although I suspect it fails through circularity. (But this is precisely one of the accusations that critics made against cladistics: the decision that a character is an apomorphy is informed by a prior view that the group it defines is a clade.) You and I may agree that adding "secondarily" fails to say anything extra, but I think that reliable sources do not, so we should be cautious about removing it.
An earlier version of the article said:
Peter Brown changed this to remove the 'subjective' wording "inferred", "appear to be" and "implies", with the edit summary "Deleted phrases implying that polyphyly is subjective. Polyphyly does not depend on human inference."
Now I agree that polyphyly is objective: a set of taxa either is or is not polyphyletic (based on a given definition). However, my worry is that stated baldly this doesn't convey the science involved. We don't know for sure whether a character is a homoplasy; it's a scientific hypothesis that it is and hence it's a scientific hypothesis that a set of taxa is a polyphyly. Polyphyly does not depend on human inference, but whether or not we believe that a set of taxa constitutes a polyphyly does depend on human inference. I'm not quite sure how this is best conveyed, though. Peter coxhead ( talk) 15:17, 3 August 2013 (UTC)
Ignoring parentheses, the first two sentences of the definition at Cladistics#Terminology for character states read:
Both crocodilians and insects have certainly inherited jointed legs from their ancestors so, from the first sentence, it seems that jointed legs are a plesiomorphy of the crocodilians as well as of the insects. Neither Crocodilia nor Insecta is nested within the other. Does that mean, from the second sentence, that the possession of jointed legs is a symplesiomorphy of these two clades? If so, this would be a good example to use. Peter Brown ( talk) 23:01, 12 October 2013 (UTC)
Paragraph 1: | What would not be evidence that A and B fall into a clade which excludes C would be that A and B retain some character from an ancestor of A, B and C, but that C or C's ancestors lost it.
The fact that Gila monsters and monitor lizards have legs retained from an ancestor of Gila monsters, monitor lizards, and snakes but snakes' ancestors lost them is evidence that Gila monsters and monitor lizards fall into a clade (specifically Anguimorpha) that excludes snakes, isn't it?
|
Paragraph 2: | The character "possesses internal gills". . .offers no evidence that cartilaginous fish and ray-finned fish form a clade which excludes tetrapods.
As with the Anguimorpha, I'd say that it does offer strong evidence. As it happens, there is even stronger evidence that there is no such clade. I suggest that consideration of evidence be excluded from these formulations; what matters are the traits and the phylogeny.
|
Paragraph 3: | "Possesses internal gills". . .is a synapomorphy of cartilaginous fish and ray-finned fish relative to exchinoderms.
For symplesiomorphies, your preferred schema is "σ is a symplesiomorphy of A and B relative to C". For synapomorphies, though, do we want the "relative to" part? Can't we just say that "Possesses internal gills" is a synapomorphy of cartilaginous fish and ray-finned fish?
|
Paragraph 4: | Same problem as in Paragraph 3. Also, are you saying that synapsids don't have epidermal scales on the head and body? What about armadillos?
|
I think I need a diagram to help me explain what I mean (which is hopefully what Hennig meant, but I find this stuff confused in the literature).
Consider three features distributed among four groups like the following. "Yes" means "has or has lost".
Group | Feature 1 | Feature 2 | Feature 3 |
---|---|---|---|
A | yes | no | no |
B | no | no | no |
C | yes | yes | yes |
D | yes | yes | no |
The universe of discourse consists only of A, B, C and D and Features 1, 2 and 3.
Then in the Hennigian approach, we look for apomorphies.
Then the only possible cladogram (bar rotations) is:
−−− |
| ||||||||||||||||||
So far, so good. What about (sym)plesiomorphies? Since Feature 1 is a synapomorphy of A+C+D, it's a symplesiomorphy of any subset, i.e. A+C, A+D, C+D. C+D do form a clade but their shared possession of Feature 1 offers no evidence for this in the Hennigian approach because it's a symplesiomorphy with respect to A (in my terminology). [In other phylogenetic methods, e.g. parsimony, it would add support for this cladogram.] If Feature 3 is a radical innovation, and Feature 2 only a minor change, in traditional Linnean classification we could argue for putting A and D in one (paraphyletic) group and C in another. But there's no Hennigian evidence for this: all that A and D share is Feature 1, which is a symplesiomorphy (with respect to C). What about the absence of Feature 3? That's a (kind of) symplesiomorphy, in this case inherited by A, B and D from their common ancestor, but C has "lost" the absence. The absence of Feature 3 can define a paraphyletic group, but not a Hennigian clade, which must have a synapomorphy.
In the strict Hennigian approach, the only groups of real interest are monophylies; paraphylies and polyphylies are just different kinds of non-monophylies. In the same way, the only features of real interest are synapomorphies – those features which define a clade because they are shared by all members of the clade and are derived from the ancestor of the clade (although they may have been lost later). Symplesiomorphies are just features which aren't synapomorphies and hence characterize non-monophylies.
A synapomorphy necessarily involves at least one group outside the clade – an outgroup in modern phylogenetic studies – from which the "morphy" is "apo". That's what I mean by "with respect to". (For example, in my cladogram above, A is outside the clade C+D because it doesn't have the synapomorphy Feature 2. Feature 2 is a synapomorphy of C+D with respect to A – or indeed with respect to any other group.)
Can we describe Feature 1 as a synapomorphy of C+D? The simplest answer is "no". An "apo-morphy" must be "apo" something. In this case it's "apo" the absence of Feature 1. So the only group of which Feature 1 is a synapomorphy is A+C+D. Another answer, and here I think I may be departing from the Hennigian approach (although I find explanations of it unclear on this point) is that Feature 1 is a synapomorphy of C+D with respect to B. Feature 1 is a shared (i.e. syn) difference (i.e. apomorphy) of C and D from B. But it's not a shared difference of C and D from A, so it's not an "absolute" synapomorphy.
A symplesiomorphy necessarily involves at least one group within a clade whose sharing of the clade-defining feature (or possibly having lost it) is being ignored – that's what I mean by "with respect to". (For example, in my cladogram above, if we group A and D on the basis of sharing Feature 1, we're ignoring C which also has Feature 1. Feature 1 is symplesiomorphy of A and D with respect to C.) Peter coxhead ( talk) 14:22, 16 October 2013 (UTC)
Once you have defined a clade on the basis of a shared inherited feature which differentiates it from all non-members of the clade (i.e. a synapomorphy), that feature is of no value whatsoever in determining whether groups within the clade form subclades. From that point on it's a symplesiomorphy. Peter coxhead ( talk) 14:31, 16 October 2013 (UTC)
cartilaginous and ray-finned fish both possess internal gills while tetrapods don'tIt's not so simple because features can be transformed and so apparently lost. There don't have to be fully functioning internal gills; the question is whether there are any features of tetrapods which are homologous to internal gills and which can't be explained other than by having ancestors which did have internal gills. Similar features may not be homologous and homologous features may not be similar.
The fact that cartilaginous and ray-finned fish both possess internal gills and tetrapods don't is evidence in this sense that the two fish groups are members of a clade that excludes tetrapods.If tetrapods really did have no trace whatsoever of internal gills, then sure. However, embryological development as well as adult morphology shows that actually tetrapods do have features which are homologous to the internal gills of the two fish groups. (Gill slits appear in mammalian embryological development, for example.) There's no doubt that tetrapods are descended from ancestors with internal gills.
The term Stem-based taxon redirects to this article, which however does not even mention it! Could the term please be placed in boldface in the lead, with a brief explanation, and then discussed somewhere in the article? Chiswick Chap ( talk) 15:51, 23 October 2013 (UTC)
It gets even worse than the article and talk page seem to have suggested. You could in theory have 2 different (yet maybe closely-related) species/varieties experience a common environmental factor and thus have a preference for the same mutation/s. Eyes for example seem to have evolved several times since animal life evolved. Granted, they aren't physically identical forms of vision. Actually, I was wrong. It's more like dozens. O_o
How do you contend with timelines of family/group/genus/species/subspecies trees that seem paradoxical because of this issue? The article implies that only one of the cladistic trees is accurate, but it seems that simplistic trees might ALL be wrong for a given group of species. 2601:1:9280:155:6155:1881:4B26:F3D4 ( talk) 12:25, 6 March 2014 (UTC)
Could you have a look at this effort, here, to use clade diagrams to summarize pharma business mergers and acquisitions (M&A). My take at present is that the images created are devoid of standard quantitative meaning—nothing is captured by vertical and horizontal line lengths, as far as I can tell—and so they are a misapplication of this maths/graphic presentation method. Moreover, I argue that they are misleading (presenting a time axis, but not making spacing of events proportionate to the historical time differences), much harder to maintain (consider adding entries to a std Table versus this graphic), more likely to diminish article quality (in their ambiguity of content, again, over a std Table with clear headings), and therefore practically amenable to decay as a result. I would add to this, in this esteemed cladistics context, that they would make those who trained us, and other purists in methodology and meaning… turn in their graves/beds. After having a look at the User page and at a couple of pages linked on that sandbox page, leave your opinion [at the link give below], regarding the overall effort? Thanks for your opinion. Cheers. Le Prof Leprof 7272 ( talk) 01:37, 23 March 2016 (UTC)
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![]() | This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
The opening definitions are very confusing and appear to be confusing/confounding cladistics with phylogenetics, among other things.
Definition #1- Cladistics is not "the science of phylogenetics." This sentence has two problems. First, cladistics is a starting point method for figuring out a phylogeny. It is not the actual making a phylogeny, several of which could come from one cladistic analysis (see Cladograms and Phylogenetic Trees, Wiley EO, Systematic Zoology, 1979). Second, and in a similar vein, it is not "the" method as in the only one for figuring out a phylogeny (again, it doesn't even figure them out in the first place it is only a starting point). Third, and MOST importantly, this definition really doesn't tell the reader anything about cladistics. It just tells the reader that it is "a method", but never actually describes the method (in fact no where in the article is this so called "method of cladistics" ever defined or described, not even telling the reading what a shared derived characteristic is). Therefore I wanted to replace the opening definition with: "A method for establishing the relationships of various individuals, items, concepts, etc through the use of shared characteristics." This definition is backed up with the following citations:
"Cladistics: Theory and Practice of Parsimony Analysis" page 1: "Cladistics is a method of classification that groups taxa hierarchically into sets and subsets." page 2: "The aim of cladistics is to establish sister-group relationships, and the concept of two taxa being more closely related than either is to a third." "Sister groups are hypothesized through the analysis of characters"
"Transformed Cladistics, Taxonomy and Evolution" page 68: "On the basis of a comparison of organisms, perceived similarities are utilized to choose those characters that will be used for more detailed comparisons leading to the construction of a cladogram. Central to this endeavor is the recognition of shared derived characters."
UCMP University Of California Museum of Paleontology Website on cladistics: "Cladistics is a particular method of hypothesizing relationships among organisms." "The basic idea behind cladistics is that members of a group share a common evolutionary history, and are "closely related," more so to members of the same group than to other organisms. These groups are recognized by sharing unique features which were not present in distant ancestors."
Definition #2- This is confusing due to its wording. Its original form leaves it unclear if the words "phylogenetic systematics" are included because they are somehow a synonym for cladistics (if so why is that down here in definitions) or whether it is a whole different field and hence no longer a definition of the main heading word of the page. I tried to emphasize that the second definition is a narrower form of the first definition and that it goes by a specific name (phylogenetic systematics). Hence my definition: "phylogenetic systematics, is a narrower and more formal version of the above which uses the principle of only naming clades as its source of information for taxonomy. This is sometimes pejoratively called "cladism."" — Preceding unsigned comment added by Nathank2 ( talk • contribs) 21:21, 29 October 2012 (UTC)
Nathank2 ( talk) 00:06, 30 October 2012 (UTC)
Looking back over the old revisions of this article, things seem to have been clearer before. The very old version from [ 09:22, 6 June 2003] is almost exactly what I am suggesting. It's clear and understandable for a lay person. Version [ 20:23, 19 January 2007] is a little more convoluted and difficult to understand at the beginning, but the entirety of the opening section is very good and does a good job of giving a basic explanation of the whole concept. Nathank2 ( talk) 16:14, 30 October 2012 (UTC)
Nathank2 ( talk) 21:11, 30 October 2012 (UTC)
Hello, I need a help from people with knowledge in systematics and taxonomy to discuss the Template:SysTax. This template was removed from the pages where it appears for discussion and improvment. Thanks Zorahia ( talk) 15:22, 22 March 2013 (UTC)
RE: Maas, Philipp (2010), "Text Genealogy, Textual Criticism and Editorial Technique", in Jürgen, Hanneder; Maas, Philipp, Wiener Zeitschrift für die Kunde Südasiens (Vienna: Austrian Academy of Sciences), 52-53: 63–120, doi:10.1553/wzks2009-2010s63
The article title is wrong. At pages 63-120 of this volume, Maas's article title is "Computer Aided Stemmatics — The Case of Fifty-Two Text Versions of Carakasaṃhitā Vimānasthāna 8.67-157."
The title given to this issue of the journal, which Maas CO-edited, is indeed Text Genealogy, Textual Criticism and Editorial Technique. But in the references, that title for the journal is given as the title for the article. It is unclear what is being cited. — Preceding unsigned comment added by 50.133.222.248 ( talk) 05:15, 19 May 2013 (UTC)
Peter Brown deleted my edits to the cladistic pages here, suggesting that they gave too much credit to Steve Farris. I see that he is not a systematist, and I wonder just how he justifies his editorial choices, given that the section called for greater detail, which I provided. Is he suggesting that the historical information I provided is not true? - Andy Brower — Preceding unsigned comment added by Abrower ( talk • contribs) 13:00, 20 May 2013 (UTC)
See here. A similar example, which thankfully hasn't escalated to an edit-war due to the timely intervention-edit of another user, can be found here. From my point of view, this is something trivial... Thanatos| talk 19:59, 24 May 2013 (UTC)
The first sentence of the page currently has two citations for the parenthetical statement that the word "cladistics" derives from Greek κλάδος, klados, i.e. "branch". I see the first one as spurious ( "cladistics". Online Etymology Dictionary.) because it says nothing about this, but the editor who inserted it has repeatedly reverted me. Could someone else please look at this matter? Thanks. Sminthopsis84 ( talk) 20:01, 24 May 2013 (UTC)
What is the difference (if any) between cladistics and classic biological taxonomy? How do they relate to one another? What was there before cladistics was invented? Or is cladistics just a new name for an old discipline? The article on "Taxonomy (biology)" mentions "cladistic" only in passing, without any explanation of its role. — Preceding unsigned comment added by 213.207.170.238 ( talk) 07:49, 29 July 2013 (UTC)
In Cladistics#Terminology for taxa is the statement:
Is saying that the character states were "inherited by its descendants (unless secondarily lost)" just a fancy way of saying that the states were inherited by its descendants unless they weren't? If so, the phrase is vacuous and could be omitted. Peter Brown ( talk) 02:12, 2 August 2013 (UTC)
A clade is characterized by one or more apomorphies: derived character states inferred to have been present in the first member of the taxon and not inherited by any other taxa.This isn't right, because it doesn't say that the apomorphies were inherited by that taxon, only that they weren't inherited by any other. If you omit the parenthesised part, you get
A clade is characterized by one or more apomorphies: derived character states inferred to have been present in the first member of the taxon, inherited by its descendants, and not inherited by any other taxa.Since bare plurals in English often logically mean "all", this can be misread as
... inherited by all its descendants ..., so the qualification is needed to avoid this interpretation. A fuller statement might be something like
A clade is characterized by one or more apomorphies: derived character states inferred to have been present in the first member of the taxon, present through inheritance in most of its descendants (but not necessarily all since they may have lost it), and not inherited by any other taxa.Peter coxhead ( talk) 09:14, 2 August 2013 (UTC)
was secondarily lost" is just a misleading way of saying "was not inherited– well, this is at the heart of our disagreement. Clearly "was lost" is just a way of saying "was not inherited". However, the addition of "secondarily" here is an attempt to say more, although I suspect it fails through circularity. (But this is precisely one of the accusations that critics made against cladistics: the decision that a character is an apomorphy is informed by a prior view that the group it defines is a clade.) You and I may agree that adding "secondarily" fails to say anything extra, but I think that reliable sources do not, so we should be cautious about removing it.
An earlier version of the article said:
Peter Brown changed this to remove the 'subjective' wording "inferred", "appear to be" and "implies", with the edit summary "Deleted phrases implying that polyphyly is subjective. Polyphyly does not depend on human inference."
Now I agree that polyphyly is objective: a set of taxa either is or is not polyphyletic (based on a given definition). However, my worry is that stated baldly this doesn't convey the science involved. We don't know for sure whether a character is a homoplasy; it's a scientific hypothesis that it is and hence it's a scientific hypothesis that a set of taxa is a polyphyly. Polyphyly does not depend on human inference, but whether or not we believe that a set of taxa constitutes a polyphyly does depend on human inference. I'm not quite sure how this is best conveyed, though. Peter coxhead ( talk) 15:17, 3 August 2013 (UTC)
Ignoring parentheses, the first two sentences of the definition at Cladistics#Terminology for character states read:
Both crocodilians and insects have certainly inherited jointed legs from their ancestors so, from the first sentence, it seems that jointed legs are a plesiomorphy of the crocodilians as well as of the insects. Neither Crocodilia nor Insecta is nested within the other. Does that mean, from the second sentence, that the possession of jointed legs is a symplesiomorphy of these two clades? If so, this would be a good example to use. Peter Brown ( talk) 23:01, 12 October 2013 (UTC)
Paragraph 1: | What would not be evidence that A and B fall into a clade which excludes C would be that A and B retain some character from an ancestor of A, B and C, but that C or C's ancestors lost it.
The fact that Gila monsters and monitor lizards have legs retained from an ancestor of Gila monsters, monitor lizards, and snakes but snakes' ancestors lost them is evidence that Gila monsters and monitor lizards fall into a clade (specifically Anguimorpha) that excludes snakes, isn't it?
|
Paragraph 2: | The character "possesses internal gills". . .offers no evidence that cartilaginous fish and ray-finned fish form a clade which excludes tetrapods.
As with the Anguimorpha, I'd say that it does offer strong evidence. As it happens, there is even stronger evidence that there is no such clade. I suggest that consideration of evidence be excluded from these formulations; what matters are the traits and the phylogeny.
|
Paragraph 3: | "Possesses internal gills". . .is a synapomorphy of cartilaginous fish and ray-finned fish relative to exchinoderms.
For symplesiomorphies, your preferred schema is "σ is a symplesiomorphy of A and B relative to C". For synapomorphies, though, do we want the "relative to" part? Can't we just say that "Possesses internal gills" is a synapomorphy of cartilaginous fish and ray-finned fish?
|
Paragraph 4: | Same problem as in Paragraph 3. Also, are you saying that synapsids don't have epidermal scales on the head and body? What about armadillos?
|
I think I need a diagram to help me explain what I mean (which is hopefully what Hennig meant, but I find this stuff confused in the literature).
Consider three features distributed among four groups like the following. "Yes" means "has or has lost".
Group | Feature 1 | Feature 2 | Feature 3 |
---|---|---|---|
A | yes | no | no |
B | no | no | no |
C | yes | yes | yes |
D | yes | yes | no |
The universe of discourse consists only of A, B, C and D and Features 1, 2 and 3.
Then in the Hennigian approach, we look for apomorphies.
Then the only possible cladogram (bar rotations) is:
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So far, so good. What about (sym)plesiomorphies? Since Feature 1 is a synapomorphy of A+C+D, it's a symplesiomorphy of any subset, i.e. A+C, A+D, C+D. C+D do form a clade but their shared possession of Feature 1 offers no evidence for this in the Hennigian approach because it's a symplesiomorphy with respect to A (in my terminology). [In other phylogenetic methods, e.g. parsimony, it would add support for this cladogram.] If Feature 3 is a radical innovation, and Feature 2 only a minor change, in traditional Linnean classification we could argue for putting A and D in one (paraphyletic) group and C in another. But there's no Hennigian evidence for this: all that A and D share is Feature 1, which is a symplesiomorphy (with respect to C). What about the absence of Feature 3? That's a (kind of) symplesiomorphy, in this case inherited by A, B and D from their common ancestor, but C has "lost" the absence. The absence of Feature 3 can define a paraphyletic group, but not a Hennigian clade, which must have a synapomorphy.
In the strict Hennigian approach, the only groups of real interest are monophylies; paraphylies and polyphylies are just different kinds of non-monophylies. In the same way, the only features of real interest are synapomorphies – those features which define a clade because they are shared by all members of the clade and are derived from the ancestor of the clade (although they may have been lost later). Symplesiomorphies are just features which aren't synapomorphies and hence characterize non-monophylies.
A synapomorphy necessarily involves at least one group outside the clade – an outgroup in modern phylogenetic studies – from which the "morphy" is "apo". That's what I mean by "with respect to". (For example, in my cladogram above, A is outside the clade C+D because it doesn't have the synapomorphy Feature 2. Feature 2 is a synapomorphy of C+D with respect to A – or indeed with respect to any other group.)
Can we describe Feature 1 as a synapomorphy of C+D? The simplest answer is "no". An "apo-morphy" must be "apo" something. In this case it's "apo" the absence of Feature 1. So the only group of which Feature 1 is a synapomorphy is A+C+D. Another answer, and here I think I may be departing from the Hennigian approach (although I find explanations of it unclear on this point) is that Feature 1 is a synapomorphy of C+D with respect to B. Feature 1 is a shared (i.e. syn) difference (i.e. apomorphy) of C and D from B. But it's not a shared difference of C and D from A, so it's not an "absolute" synapomorphy.
A symplesiomorphy necessarily involves at least one group within a clade whose sharing of the clade-defining feature (or possibly having lost it) is being ignored – that's what I mean by "with respect to". (For example, in my cladogram above, if we group A and D on the basis of sharing Feature 1, we're ignoring C which also has Feature 1. Feature 1 is symplesiomorphy of A and D with respect to C.) Peter coxhead ( talk) 14:22, 16 October 2013 (UTC)
Once you have defined a clade on the basis of a shared inherited feature which differentiates it from all non-members of the clade (i.e. a synapomorphy), that feature is of no value whatsoever in determining whether groups within the clade form subclades. From that point on it's a symplesiomorphy. Peter coxhead ( talk) 14:31, 16 October 2013 (UTC)
cartilaginous and ray-finned fish both possess internal gills while tetrapods don'tIt's not so simple because features can be transformed and so apparently lost. There don't have to be fully functioning internal gills; the question is whether there are any features of tetrapods which are homologous to internal gills and which can't be explained other than by having ancestors which did have internal gills. Similar features may not be homologous and homologous features may not be similar.
The fact that cartilaginous and ray-finned fish both possess internal gills and tetrapods don't is evidence in this sense that the two fish groups are members of a clade that excludes tetrapods.If tetrapods really did have no trace whatsoever of internal gills, then sure. However, embryological development as well as adult morphology shows that actually tetrapods do have features which are homologous to the internal gills of the two fish groups. (Gill slits appear in mammalian embryological development, for example.) There's no doubt that tetrapods are descended from ancestors with internal gills.
The term Stem-based taxon redirects to this article, which however does not even mention it! Could the term please be placed in boldface in the lead, with a brief explanation, and then discussed somewhere in the article? Chiswick Chap ( talk) 15:51, 23 October 2013 (UTC)
It gets even worse than the article and talk page seem to have suggested. You could in theory have 2 different (yet maybe closely-related) species/varieties experience a common environmental factor and thus have a preference for the same mutation/s. Eyes for example seem to have evolved several times since animal life evolved. Granted, they aren't physically identical forms of vision. Actually, I was wrong. It's more like dozens. O_o
How do you contend with timelines of family/group/genus/species/subspecies trees that seem paradoxical because of this issue? The article implies that only one of the cladistic trees is accurate, but it seems that simplistic trees might ALL be wrong for a given group of species. 2601:1:9280:155:6155:1881:4B26:F3D4 ( talk) 12:25, 6 March 2014 (UTC)
Could you have a look at this effort, here, to use clade diagrams to summarize pharma business mergers and acquisitions (M&A). My take at present is that the images created are devoid of standard quantitative meaning—nothing is captured by vertical and horizontal line lengths, as far as I can tell—and so they are a misapplication of this maths/graphic presentation method. Moreover, I argue that they are misleading (presenting a time axis, but not making spacing of events proportionate to the historical time differences), much harder to maintain (consider adding entries to a std Table versus this graphic), more likely to diminish article quality (in their ambiguity of content, again, over a std Table with clear headings), and therefore practically amenable to decay as a result. I would add to this, in this esteemed cladistics context, that they would make those who trained us, and other purists in methodology and meaning… turn in their graves/beds. After having a look at the User page and at a couple of pages linked on that sandbox page, leave your opinion [at the link give below], regarding the overall effort? Thanks for your opinion. Cheers. Le Prof Leprof 7272 ( talk) 01:37, 23 March 2016 (UTC)
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