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Author Topic:   On Transitional Species (SUMMATION MESSAGES ONLY)
pandion
Member (Idle past 1316 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 16 of 314 (505118)
04-07-2009 7:41 PM
Reply to: Message 12 by kuresu
04-07-2009 1:48 PM


kuresu writes:

Wait, what?

I thought that was basically the whole point of transitionals. That they show the potential evolutionary lineage.


But they are not meant to indicate ancestry. Let me give you an example. Theropod dinosaurs are also transitional between Saurischia and birds. That is not to say that Dilophosaurus, or any other Theropoda, is an ancestor to birds. But Theropods begin to show derived traits that are true of later dinosaurs and birds that are not found in earlier, more primitive dinosaurs. One Theropod lineage evolved into the Tetanurae. Allosaurus was one, but no one seriously claims that birds are descended from Allosaurus. One lineage of Tetanurae (not Allosaurus) evolved into the Coelurosauria. But Allosaurus shows traits of the earlier theropods (like Dilophosaurus) and also some new derived traits that are also present in the Coelurosauria (like the Tyrannosauridae). And while it would be silly to claim that T. rex is ancestral to birds, it is transitional between the Saurischia and the later Maniraptora (like the Dromaeosauridae). Again there is a mix of early traits and derived traits (like feathers). But they are not ancestral to birds. They share a common ancestor with birds.

You want to ask how a fish became a frog, that's where transitionals come in.

I could give you a list of 20 or so fossils that are transitional between fish and a frog. However, it is very unlikely that any of them are a direct ancestor of frogs. They are representative of the types of organisms that we expect to find that show a mixture of primitive traits along with derived traits.

You want to ask how a frog become a reptile, that's where transitionals come in.

Sorry, but that is grossly incorrect. Frogs and the like are far from the lineage that led to reptiles from the early amphibians.

You want to ask how some cattle-like creature became a whale, that's where transitionals come in.

Whales did not evolve from cattle like creatures. The earliest whales more resembled dogs than cattle.

You want to ask how Hyracotherium became the modern horse, that's where transitionals come in.

The status of Hyracotherium as an equid is not clear. It may not be very close to the lineage that led to horses.

Even if the example we have isn't B, it still shares an ancestor with B. If it doesn't have such an ancestral link, it's worthless as a transitional, no?

But that's the point. The best that can be saidd is that a transitional species shares a common ancestor with the lineage under study. Thus, maniraptors share a common ancestor with the Tyrannosauridae. It doesn't mean that T. rex is an ancestor to anything.

I have no idea of what your charts are supposed to represent.

Obviously, it was an example to get the point across. I don't see what the problem with being a non-interbreeding population is, since a transitional species obviously doesn't interbreed with it's parent or daughter species. As to being the same species, I'm talking about a genealogical family tree for crying out loud. Did the allegory completely miss? Besides, the point was that you use the middle to show how the changes appeared from A to C, and one species or many can show that.

You're somewhat correct. Transitional species do not interbreed with parent or descendent species. However, evolution takes place in populations, not individuals. And you're mother is not a transitional species between your grandparents and you in any sense relevant to biological evolution. So, to answer your question, yes, you missed completely. Mostly because you give the impression that it can be determined with any sort of confidence that one fossil species is ancestral to any other. An exception that was pointed our is in the case of foraminifera and radiolaria and the like. The ancestor/descendant lineages can be traced in the fine sediments.

This message is a reply to:
 Message 12 by kuresu, posted 04-07-2009 1:48 PM kuresu has responded

Replies to this message:
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pandion
Member (Idle past 1316 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 17 of 314 (505119)
04-07-2009 7:43 PM
Reply to: Message 14 by Larni
04-07-2009 2:09 PM


Are you the Pandion from 4Forums.com?

Yes. That's me.

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Richard Townsend
Member (Idle past 3048 days)
Posts: 103
From: London, England
Joined: 07-16-2008


Message 18 of 314 (505121)
04-07-2009 7:51 PM


I've often heard people say that all species are 'transitional' - but is that really the case? Transitional carries the overtone of 'between two distinct groups'. Not every species can carry the mixed set of characters that this implies - or am I wrong about this?

In fact, I would expect (based on ignorance!) that only a very small subset of species would meet this definition.

Please feel free to correct me on this

Rich


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NosyNed
Member
Posts: 8866
From: Canada
Joined: 04-04-2003
Member Rating: 7.5


Message 19 of 314 (505123)
04-07-2009 9:10 PM
Reply to: Message 18 by Richard Townsend
04-07-2009 7:51 PM


groups
I've often heard people say that all species are 'transitional' - but is that really the case? Transitional carries the overtone of 'between two distinct groups'. Not every species can carry the mixed set of characters that this implies - or am I wrong about this?

In fact, I would expect (based on ignorance!) that only a very small subset of species would meet this definition.

You are thinking of a "group" as being something large and far apart like reptiles and mammals. That maybe true but a group can be a genus or even species where the transitional and both of the other parts of the transition maybe darned hard to tell apart.


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RAZD
Member
Posts: 20254
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 4.0


Message 20 of 314 (505124)
04-07-2009 9:29 PM
Reply to: Message 18 by Richard Townsend
04-07-2009 7:51 PM


I've often heard people say that all species are 'transitional' - but is that really the case? Transitional carries the overtone of 'between two distinct groups'. Not every species can carry the mixed set of characters that this implies - or am I wrong about this?

Yes and no. The problem is that you have not defined "distinct" sufficiently to say, and this leaves it open for subjective interpretation.

In one very real sense each existing species population is distinct from their parent population and from their offspring population - each group has different hereditary traits ... but the difference may not be that significant in terms of natural selection, or sufficient to satisfy your impression of what is a "distinct" difference.

What you have is a constant succession of individual organisms within a population, so the mix is constantly changing, just as the cells in your body are constantly changing as new cells replace old, worn out ones, or ones that are damaged. Over time the accumulated changes become more and more "distinct" between the beginning population and the most recent population.

During your lifetime your body goes through a succession of stages as you grow from conception to birth to childhood to adult to old geezer (like me), and at every stage you think of your body as being complete. Some stages occur rapidly and some stages occur slowely, but there is never a time when you are not in transition from one stage to another.

None of these stages occur all at once, or only go through a single transitional phase, but they occur over time while the changes accumulate, and one day you wake up and say "dang, I'm OLD, dad-burn-it!"

If you are lucky (or have the right combination of beneficial hereditary traits) you will live a long time, possibly giving birth to many other species individuals.

In fact, I would expect (based on ignorance!) that only a very small subset of species would meet this definition.

Please feel free to correct me on this

This would only be true if you expected ALL the transition from one "distinct (to you) group" to another "distinct (to you) group" to occur within ONE contemporary population.

The more difference you require for one group to be distinctive (to you) from another, the more generations you should expect the transitional period to cover, with the transition spread out over many stages of growth and succession of individual cells individuals, just as you don't expect the growth from infant to ancient to occur overnight.

Enjoy.


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by our ability to understand
Rebel American Zen Deist
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This message is a reply to:
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AustinG
Member (Idle past 3484 days)
Posts: 36
Joined: 04-06-2009


Message 21 of 314 (505126)
04-07-2009 10:13 PM
Reply to: Message 20 by RAZD
04-07-2009 9:29 PM


Good post RAZD.

Edited by AustinG, : forgot which thread I was on O.o


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pandion
Member (Idle past 1316 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 22 of 314 (505133)
04-07-2009 11:53 PM
Reply to: Message 18 by Richard Townsend
04-07-2009 7:51 PM


I've often heard people say that all species are 'transitional' - but is that really the case?

My first thoughts were as follows. "No. Extant species can only be transitional from an ancestral species to something that they will become in the future. If a species goes extinct, then it cannot be transitional." But those thoughts were wrong. You see, we can't know for sure from the fossil record whether any species went extinct without further evolution. But that doesn't matter. That there are transitional species is a prediction of the evolutionary theory of common descent. We don't know if Archaeopteryx went extinct or not. That doesn't change its status as a transitional species. That status is derived from the theory that birds are descended from dinosaurs. If that is true, then we should find fossil evidence of creatures of the correct age that have a mix of traits of two (and only two) groups of organisms; dinosaurs and birds. Archy is just such a fossil. Several other examples have been found in various locations around the world. The idea is that evolution is not a ladder of descent, but a matter of constant radiation and re-radiation of species. Any one of the radiations from the lineage between dinosaur and bird is a transitional species.

This same logic of prediction holds true for any transition. We can find hundreds of fossils that demonstrate the predicted traits of these transitions: jawless fish to sharks and rays; jawless fish to bony fish; bony fish to early amphibians; early amphibians to modern amphibians; modern amphibians to frogs and salamanders; early amphibians to early reptiles; and so on. That includes the evolution of dinosaurs from reptiles and the evolution of birds from dinosaurs.

So, if a species goes extinct it can still be a transitional if it shows the mix of traits between a shared ancestor group and the descendants from a related species. In fact, I suspect that most transitional fossils are of this type (except for marine microfossils where the transition can be traced in detail).

Good question!


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kuresu
Member (Idle past 829 days)
Posts: 2544
From: boulder, colorado
Joined: 03-24-2006


Message 23 of 314 (505178)
04-08-2009 12:41 PM
Reply to: Message 16 by pandion
04-07-2009 7:41 PM


And you're mother is not a transitional species between your grandparents and you in any sense relevant to biological evolution.

No shit. And I never claimed that to be the case. The entire point behind my example was that transitions are through time, not environment. You have a before, you have an after, and the transitional fills in the between time. When I bring up the family tree, I say "In that sense", which means I'm not using any technical examples of transitional species. My goal was to use a very simple and easy to understand example, given that the thread's author wasn't exactly being all that technical. That's what I meant when I asked if the allegory completely missed: did you miss that I wasn't being technical? That I wasn't actually saying that the family tree is a real transitional species. That I was being very simplistic. I wasn't asking whether you thought it was a bad example, as you obviously do.

Again, my point was that transitionals are in time, not environment. My point was not to pick out all the fun little caveats about evolution or evolutionary history we have to keep in mind. Sorry I'm not allowed to be so simple.

Theropod dinosaurs are also transitional between Saurischia and birds...But they are not ancestral to birds. They share a common ancestor with birds.

Then I don't see how you could say that they are transitionals between saurischia and birds. But then, maybe I'm misunderstanding what you wrote. I was under the assumption that birds are most likely descended from a group of therapods, so therapods would certainly be transitionals from the earlier group and birds. But if birds aren't even from therapods, then therapods are fairly useless as transitionals, because then the similarities would be from convergent evolution.

I have no idea of what your charts are supposed to represent.

It would help if the first line in both charts had lined up properly. Somehow the forum shunted them to the left. The point was that unless (D) shares a common ancestor with (B), it is useless as a transitional between (A) and (E,F). So transitionals have to share some ancestry at the least and be close to the line that did continue. We need, to continue with the family allegory, an uncle or aunt if we don't have the parent. Anything further removed is really quite useless.

Whales did not evolve from cattle like creatures. The earliest whales more resembled dogs than cattle.

Whales descended from most likely from artiodactyls, which are ungulates. This group of ungulates currently includes deer, giraffes, antelopes, hippos, and cattle among many others. If they didn't descend from artiodactyls, it was from a different ungulate group, mesonychids, which are now extinct.

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Blue Jay
Member (Idle past 1014 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 24 of 314 (505187)
04-08-2009 4:28 PM
Reply to: Message 16 by pandion
04-07-2009 7:41 PM


Transitional Semantics
Hi, Pandion.

Welcome to EvC!

pandion writes:

And while it would be silly to claim that T. rex is ancestral to birds, it is transitional between the Saurischia and the later Maniraptora (like the Dromaeosauridae). Again there is a mix of early traits and derived traits (like feathers). But they are not ancestral to birds. They share a common ancestor with birds.

I rather agree with Kuresu. You could say that a certain intermediate characteristic of T. rex is transitional between the homologous characteristic in plesiomorphic Saurischia and the homologous characteristic in Maniraptora, but to label T. rex as a transitional fossil between the two does carry with it the connotation of ancestry.

I don't know the phylogenetic relationshps within Saurischia very well, but if the Maniraptora are thought to have evolved from within the Coelurosauria, then you could call the Coelurosauria a transitional clade. But you can't really justify calling all individual coelurosaurians transitional. This is largely because the fossil record of theropods is relatively complete: in a group with only two or three known species, usage of the term "transitional" is (expectedly) less rigid.

For most transitional fossils, such as Archaeopteryx, much of the detailed phylogeny is unknown, so we call it transitional, not because it is definitely the ancestor of all birds itself, but because it is the only known member of a group that we are quite certain is transitional.

The same goes with Schinderhannes, the "transitional" proto-arthropod: it lived in the Devonian period, but true arthropods, which are thought to be derived from Schinderhannes's clade, were already abundant in teh Cambrian. But, since Schinderhannes is the only known representative of the clade that bridges the gap between Dinocarida/Anomalocarida and Arthropoda, we call it "transitional." If we had a better fossil history than we do, we would likely not refer to Schinderhannes as transitional (although we would still consider the large clade containing it to be transitional).

-----

I think the word "transitional" is heavily reliant on context for meaning, which is why creationists have had such a heyday making all kinds of ludicrous claims about it.

-----

For Kuresu: if you put the dBCode "code" around your diagrams, it preserves your spacing, so your dendrograms will come out looking like dendrograms instead of left-justified text.


-Bluejay/Mantis/Thylacosmilus

Darwin loves you.


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pandion
Member (Idle past 1316 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 25 of 314 (505210)
04-09-2009 2:26 AM
Reply to: Message 23 by kuresu
04-08-2009 12:41 PM


kuresu writes:

No shit. And I never claimed that to be the case.

Your potty mouth aside, that is exactly what you claimed.

The entire point behind my example was that transitions are through time, not environment.

Then why didn't you say so? Your example gives the impression that you believe that a transitional species somehow indicates knowledge of ancestry and descendants.

You have a before, you have an after, and the transitional fills in the between time. When I bring up the family tree, I say "In that sense", which means I'm not using any technical examples of transitional species. My goal was to use a very simple and easy to understand example, given that the thread's author wasn't exactly being all that technical.

But your example was terrible and gives the wrong impression of what biologists and paleontologists mean when they discuss transitionals. Your example was quite simple and easy to understand, but it also is misleading because it is so grossly incorrect.

That's what I meant when I asked if the allegory completely missed: did you miss that I wasn't being technical?

No. That was obvious. What isn't obvious is what allegory you are talking about. You didn't present an allegory. By chance do you actually mean analogy? My point is that it is a very bad analogy.

That I wasn't actually saying that the family tree is a real transitional species. That I was being very simplistic. I wasn't asking whether you thought it was a bad example, as you obviously do.

You weren't? That wasn't clear. And certainly someone who read your post and was trying to understand the nature of a transitional species would have been mislead. Your analogy (allegory??) is typical of how creationists understand what transitional species are. If you really understand and are aware of the creationist view, why on earth would you encourage it?

Again, my point was that transitionals are in time, not environment. My point was not to pick out all the fun little caveats about evolution or evolutionary history we have to keep in mind. Sorry I'm not allowed to be so simple.

I have no problem with keeping it simple. I'm more concerned with keeping it correct.

Then I don't see how you could say that they are transitionals between saurischia and birds. But then, maybe I'm misunderstanding what you wrote. I was under the assumption that birds are most likely descended from a group of therapods, so therapods would certainly be transitionals from the earlier group and birds. But if birds aren't even from therapods, then therapods are fairly useless as transitionals, because then the similarities would be from convergent evolution.

So now you are getting down to the grandparent/parent/you line of thought again. Evidence indicates that the lineage of birds passes through the Dinosauria, Saurischia, Theropoda, Tetanurae, Coelurasauria, Maniraptora, and Avialae. At no point in that sequence can anyone point to a specific species that is ancestral to modern birds. But every single cladistic group shows transitional traits from the earliest to the latest. You do understand that saying "Theropod" when talking about the time between 230 mya and 65 mya is even less specific than saying "bird" today. My problem is that you were much too specific, indicating direct ancestry in trying to explain what a transitional is in time. Archaeopteryx is a transitional even though we can't name a specific ancestor. Archy was a Dinosauria, Saurischia, Theropoda, Tetanurae, Coelurasauria, Maniraptora, and Avialae. On the other hand, we can't point to a single lineage that is possible descended from Archy. That doesn't change the fact that Archy is an example of many species around the world that were transitional between dinosaurs and birds. One of those threads became birds, even though we don't know which one. We do have many examples of fossils that represent the expected radiation of species that show transitional traits.

It would help if the first line in both charts had lined up properly. Somehow the forum shunted them to the left.

The system deletes what it sees as unnecessary spaces.

The point was that unless (D) shares a common ancestor with (B), it is useless as a transitional between (A) and (E,F).

That's true.

So transitionals have to share some ancestry at the least and be close to the line that did continue.

OK. Not all that close since they are probably a single species of many, many others.

We need, to continue with the family allegory, an uncle or aunt if we don't have the parent. Anything further removed is really quite useless.

Again, I presume you mean analogy, since you have presented no allegory. But you aren't correct. You are still trying to narrow the field too much. We aren't talking about uncles or aunts. We are talking about huge groups of related populations that all showed transitional traits. We have fossils of only a few examples.

Whales descended from most likely from artiodactyls, which are ungulates. This group of ungulates currently includes deer, giraffes, antelopes, hippos, and cattle among many others. If they didn't descend from artiodactyls, it was from a different ungulate group, mesonychids, which are now extinct.

Indeed true. Whales did descend from artiodactyles. However, just because the species that you mention are descended from artiodactyls doesn't mean that they looked like cows. In fact, deer, giraffes, antelopes, and hippos don't look all that much like cows. But, never mind. Look up Sinonyx on Wikipedia and tell me if that looks like a cow. Why do you think that animal populations from 60 million years ago should look like members of the same taxonomic groups today?


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pandion
Member (Idle past 1316 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 26 of 314 (505214)
04-09-2009 2:54 AM
Reply to: Message 24 by Blue Jay
04-08-2009 4:28 PM


Re: Transitional Semantics
I rather agree with Kuresu. You could say that a certain intermediate characteristic of T. rex is transitional between the homologous characteristic in plesiomorphic Saurischia and the homologous characteristic in Maniraptora, but to label T. rex as a transitional fossil between the two does carry with it the connotation of ancestry.

Duh. My point was that T. rex was not ancestral to birds and I made no implication that it was. I'm not sure what you read, but it wasn't my post.

I don't know the phylogenetic relationshps within Saurischia very well, but if the Maniraptora are thought to have evolved from within the Coelurosauria, then you could call the Coelurosauria a transitional clade.

Indeed you could, and in fact it is so. In fact, that's what I said.

But you can't really justify calling all individual coelurosaurians transitional.

Why not? Do they not all have both primative and derived traits?

This is largely because the fossil record of theropods is relatively complete:

Tell me another one. That one was hilarious.

in a group with only two or three known species, usage of the term "transitional" is (expectedly) less rigid.

What group? Maniraptors? Tetanurae?


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Blue Jay
Member (Idle past 1014 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 27 of 314 (505288)
04-09-2009 8:08 PM
Reply to: Message 26 by pandion
04-09-2009 2:54 AM


Re: Transitional Semantics
Hi, Pandion.

pandion writes:

bluejay writes:

I rather agree with Kuresu. You could say that a certain intermediate characteristic of T. rex is transitional between the homologous characteristic in plesiomorphic Saurischia and the homologous characteristic in Maniraptora, but to label T. rex as a transitional fossil between the two does carry with it the connotation of ancestry.

Duh. My point was that T. rex was not ancestral to birds and I made no implication that it was. I'm not sure what you read, but it wasn't my post.

Perhaps you thought I wrote "...to label T. rex as a transitional fossil does not carry with it the connotation of ancestry"? Please notice that the word "not" does not appear in that sentence: I was, in fact, stating the exact opposite of your stance on the issue.

Duh.

-----

pandion writes:

Bluejay writes:

I don't know the phylogenetic relationshps within Saurischia very well, but if the Maniraptora are thought to have evolved from within the Coelurosauria, then you could call the Coelurosauria a transitional clade.

Indeed you could, and in fact it is so. In fact, that's what I said.

Since the literary technique of juxtaposition is apparently lost on you, let me explain it for you. The only reason I included the sentence you quoted there was to allow you the opportunity to compare it to the sentence that follows, which I’ve copied to here:

Bluejay, post 24, writes:

But you can't really justify calling all individual coelurosaurians transitional.

Juxtaposition is a method of clarification: it places a correct statement beside an incorrect statement so the reader can clearly see the difference between the two. The two sentences were meant to be read together.

-----

pandion writes:

Bluejay writes:

you can't really justify calling all individual coelurosaurians transitional.

Why not? Do they not all have both primitive and derived traits?

This comment also obviously stems from your misreading of my first sentence. I do not agree with you that your definition of “transitional” is entirely appropriate, and my entire post was an attempt to explain why.

-----

pandion writes:

Bluejay writes:

This is largely because the fossil record of theropods is relatively complete:

Tell me another one. That one was hilarious.

Is there a particular reason why you chose to skip the word “relatively” when reading my statement? This is another literary technique called “contextual cues,” whereby a writer inserts a few extra words around the word in question to denote the scope of the statement being made. In this case, the word “relatively” indicates that the writer is not stating that the fossil record of theropods is complete, but that it is more complete than other fossil groups. In the absence of a direct reference, it’s common practice to assume that the writer is comparing the subject of the sentence to something else within the discussion.

So, what fossil groups do I reference in my post? What other fossil groups are being discussed on this thread? Would you not agree that, of all the fossil groups that have so far come up in this discussion, the Theropoda indeed have the most complete fossil record? So, I would ask that you kindly refrain from your juvenile humor until after you have taken a couple technical writing courses.

Since reading is apparently not your strong suit, I fear that the rest of this post may be all in vain, but, being a stubborn and optimistic person, I will proceed anyway.

-----

Since my last angle of attack failed, let me try a simpler approach:

Notice that the word “species” is a phylogenetic term. Therefore, usage of this term implies phylogeny. Thus, usage of the term “transitional species” also implies phylogeny. If your intention is not to convey phylogeny, then you should avoid using terms that are loaded with a phylogenetic meaning.

That’s why I said you could consider T. rex’s character state transitional, but not the species itself.

But, frankly, I’m tired of debates about what terms mean. As such, this is likely my last post on the meaning of “transitional species.”

Edited by Bluejay, : I felt that the "duh" was appropriate.


-Bluejay/Mantis/Thylacosmilus

Darwin loves you.


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pandion
Member (Idle past 1316 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 28 of 314 (505323)
04-10-2009 8:39 AM
Reply to: Message 27 by Blue Jay
04-09-2009 8:08 PM


Re: Transitional Semantics
Notice that the word “species” is a phylogenetic term. Therefore, usage of this term implies phylogeny. Thus, usage of the term “transitional species” also implies phylogeny. If your intention is not to convey phylogeny, then you should avoid using terms that are loaded with a phylogenetic meaning.

That’s why I said you could consider T. rex’s character state transitional, but not the species itself.


Well, you're right in that. But then you have to consider whom is being addressed. I should have said that T. rex belonged to a transitional clade, i.e., the Coelurosauria. And, it is perfectly legitimate to call any Coelurosauria transitional simply because it is the traits of the Coelurosauria that makes it transitional.

I still giggle when I reread your statement about the "completeness" of the Coelurosauria clade. That's a good one.


This message is a reply to:
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Peter
Member (Idle past 2239 days)
Posts: 2160
From: Cambridgeshire, UK.
Joined: 02-05-2002


Message 29 of 314 (505337)
04-10-2009 11:54 AM
Reply to: Message 1 by AustinG
04-06-2009 3:06 PM


There has been an awful lot of definition splitting going on -- so I hope I don't stir it all up again :)

The initial post talked about 'Transitional Species' and then asked if every organism could be considered'Transitional'.

I think the answer is:

1. Not every organism can be considered an example of a 'Transitional Species'.

2. Every organism represents a transition from something into something else -- even if it's only a ,generation'.

To be recognised as a 'Transitional Species' surely an organism would have to show traits of a pre-existing species AND of a post-existing or contempory species.

Since one could, theoretically, have a species that represents a change from an older form to a contempory form then there might be some species living today which could be viewed as transitional.

I'm evening starting to think that pre-existing or contempory would be closer to the mark -- all three species could coincide in time and yet be related in a 'transitional species' sense.


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New Cat's Eye
Inactive Member


Message 30 of 314 (505342)
04-10-2009 12:13 PM
Reply to: Message 29 by Peter
04-10-2009 11:54 AM


To be recognised as a 'Transitional Species' surely an organism would have to show traits of a pre-existing species AND of a post-existing or contempory species.

Do you have an example of an organism that doesn't fit this criteria?

Every species has traits from a pre-existing species and the species after it will have traits from it too so....

Since one could, theoretically, have a species that represents a change from an older form to a contempory form then there might be some species living today which could be viewed as transitional.

Lets take a look.


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Click to enlarge


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I don't mean to imply that those species are closely related or anything.

But just looking at their form, the hippo, sea lion, and manatee all look like steps along the path from land mammal to sea mammal.

Could we count those as transitionals?

I'm evening starting to think that pre-existing or contempory would be closer to the mark -- all three species could coincide in time and yet be related in a 'transitional species' sense.

Like my examples above?

Edited by Catholic Scientist, : No reason given.


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