On Transitional Species (SUMMATION MESSAGES ONLY)

While it is true that all organisms can be referred to as transitional because all populations of organisms are ever changing, in biology the term transitional is most often used when discussing fossil species. These fossils show a mixture of traits, some referred to as "primitive" that come from an ancestral lineage, and some referred to as "derived" that appear in all subsequent lineages. Since living organisms don't have subsequent lineages, they are not technically transitional forms.

Indeed. Not what the term "transitional" generally means. But that's not what biologists/paleontologists mean either. A transitional species is not claimed to be descended from any specific species and is not claimed to be ancestral to any specific species. Take Archaeopteryx for example. It is obviously descended from a maniraptorian dinosaur. The specific ancestor is unknown. The maniraptorian dinosaur Compsognathus is distinguishable from Archaeopteryx because of the length of the arms. Archy also has traits that are characteristic of birds, flight feathers being the most salient, along with a opposable hallux (at least partially), furcula from fused clavicles, elongated and backward directed pubis, pneumatic bones, and so on. Archaeopteryx is a transitional species because it has primitive traits from a prior lineage (even though a specific ancestor cannot be identified), and because it has derived traits that are evident in subsequent lineages (even though no specific descendant can be identified). The point is that Archaeopteryx is found with traits that are intermediate between bird and dinosaur in geological deposits that are of the correct age. Archy may or may not be ancestral to modern birds. The point is that in Chiroptera's chart, Archy may be "D", an extinct species where "E" and "F" are modern birds. Evolution is not a ladder, where one species slowly evolves into another forever. Evolution is a bush, where one species becomes two or more over and over again. Most of those branches become extinct.Edited by pandion, : Clarification

Could be. That's why I said that Archy "may" be "D". The point is that we can't say for certain. But Archy does have the right mix of traits and it lived at the right time. It is most probably an extinct branch from the lineage that led to birds.But my main point was really your example of your grandparents, your mother, and you. You see, you are all the same species (I presume) and are not even an interbreeding population of that species. It's hard enough to explain that the term "transitional species" does not necessarily mean "descended from" nor does it mean "ancestral to". That's what creationists constantly claim and that's what your example implies. I believe that we must be careful not to give that impression when discussing transitional species.Edited by pandion, : spelling correction.

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. 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. Sorry, but that is grossly incorrect. Frogs and the like are far from the lineage that led to reptiles from the early amphibians. Whales did not evolve from cattle like creatures. The earliest whales more resembled dogs than cattle. The status of Hyracotherium as an equid is not clear. It may not be very close to the lineage that led to horses. 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. 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.

Yes. That's me.

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!

Your potty mouth aside, that is exactly what you claimed. 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. 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. 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. 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? I have no problem with keeping it simple. I'm more concerned with keeping it correct. 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. The system deletes what it sees as unnecessary spaces. That's true. OK. Not all that close since they are probably a single species of many, many others. 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. 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?

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. Indeed you could, and in fact it is so. In fact, that's what I said. Why not? Do they not all have both primative and derived traits? Tell me another one. That one was hilarious. What group? Maniraptors? Tetanurae?

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.

I completely agree. Just as Ambulocetus looked like a step along the path from land animal to sea mammal. Only if we change the definition of the word as used by biologists and paleontologists. While all of the organisms that you mentioned are most certainly a transition from some ancient, ancestral lineage to some different kind of organism some eons in the future, for the purposes of evolutionary biology and paleontology, transitional species/genera/clades show a mixture of two other groups (and only two other groups):One group is the precursor group, although it is exceedingly rare that any specific species or lineage can be identified as an ancestor. Thus Archaeopteryx has been identified as a maniraptoran coelurosaur, even though we are unable to identify any specific, less general ancestor. But Archaeopteryx also has derived traits that are not present in any ancestral lineage.The second group is the group that shows the derived traits. In the case of Archaeopteryx that group is birds. But no one seriously suggests that Archy is ancestral to birds. There is no evidence that it is true and considerable evidence that it is not true. Archy was one of many, many feathered lineages that existed. Most have gone extinct. One became modern birds. Thus, Archy is a transitional species between two large groups of organisms, dinosaurs and birds. Somewhere in the lineage of dinosaurs is one lineage that lead to Archeopteryx. Somewhere in that lineage is an ancestor of both Archy and modern birds.So the point isn't whether or not hippos, sea lions, or manatees are transitional. They are not. They may be in transition, but they have only primitive traits and derived traits; the primitive traits shared with older lineages, and the derived traits that are unique. To be considered a transitional, a fossil (I know of no non-fossil transitionals) must show a retention of primitive traits from older lineages, as well as derived traits that also appear in subsequent lineages.By the way, even though I know you weren't trying to indicate any sort of relatedness in your examples, hippos are Artiodactylas, more closely related to whales than other living groups, seals and sea lions are carnivores, related to bears/dogs/cats, and manatees are related to dugongs, whose closest living relatives may be elephants.

But that is the point. A transitional fossil, while it may be an evolutionary dead end, i.e., extinct, is an example of an organism that demonstrates a mix of primitive traits, from a more primitive lineage, and derived traits that are apparent in subsequent lineages. If there are not subsequent lineages, then, by definition, an organism cannot be transitional. Unless, of course, you wish to redefine the meaning of the word from the standard usage in biology and paleontology. Of course you don't. But on the other hand, you are using the word with a non-standard meaning when it comes to biology and paleontology. If you actually wish to discuss evolutionary biology, then you don't get to redefine the vocabulary used by evolutionary biologists and still claim to be discussing evolutionary biology. That's all well and good, except for your non-standard use of the term "transitional." In transition, OK. But transitional to what? Name it. You can't? Then whether or not it is in transition is irrelevant to whether it is a "transitional." If it goes extinct, than how is it transitional? I'm going to skip all of your other examples of unusual animals that may (or may not) evolve into other animals. They are all examples of living organisms with primitive and derived traits that are not intermediate between major lineages. Please learn what biologists and paleontologists mean when they talk about transitionals. What about it? Are you not aware that Homo erectus is not a living species? Don't you actually recognize that H. erectus is completely irrelevant to your previous discussion of transitionals? But of course it is. But H. erectus has primitive traits from a more ancient lineage as well as derived traits from subsequent lineages. There are not H. erectus alive today.What do hippos and manatees have to do with H. erectus in the context of this discussion, since hippos and manatees are living species, while H. erectus is not?

I do understand that. Actually, sometimes it seems to be for quite long periods of time. It is called "stasis." The fact that adapted populations in stable environments do not tend to change for extended periods of time has been well known for more than 30 years. Hopefully that is true. That isn't even close to what I understand as the process of evolution through random mutation and natural selection, along with several other mechanisms of evolution. You're going to have to explain before that makes sense.

Indeed true. And it is the one that is used by biologists and paleontologists. Actually, biologists and paleontologists are quite aware that fossils are only small peeks into the past. It doesn't mean that the term needs to be redefined. Believe it or not, biologists and paleontologists recognize that populations undergo change across time. In fact, biologists and paleontologists are aware that not only do populations change across time, they also know that they radiate. That is why there is rarely enough evidence to state definitively that any fossil species is descended from another fossil species. Evolution isn't a ladder with one species following another in a constant progression. Evolution is a bush, with constant radiation of populations. We can see this process happening today. Consider the 14 species of Darwin's finches, all descended from a common founding population about 2.3 mya. The closest relative in South America is a grassquit, specifically, Tiaris obscura. Molecular studies have shown that this is true. T. obscura diverged from other living Tiaris species before the Galapagos Islands were settled by these birds. Even today, the hybridization of three closely related species of Darwin's Finches has been noted. (Read "The Beak Of The Finch" by Jonathan Weiner. It won a Pulitzer Prize.So, through that fossil window we find can observe a genus such as Archaeopteryx. We can't point to an ancestor even though it is obviously a maniraptoran coelurosaur. And we can't point to any descendant, even though it is obviously a bird. Given the scarcity of the fossil record, and given that beneficial traits tend to propagate through diverging populations, the best that we can hope for is a peek through a window into the past at a related species, one that shared an ancestor with the lineage of interest, and lived at the right time, and had the expected mix of traits. These are transitionals with no implication of fixed species waiting for evolution to change them. Your second sense of the term is one held by those who don't understand what is being discussed.

Actually, your second use of the term is pretty much an unwillingness to actually define the term. It seems to be more philosophical gobblygook than anything meaningful. The first use would be pretty much clear from context. The second, with its windows onto [sic] the past and appearance of fixed species followed by the sudden onset of evolution to produce new species is drivel. So what excuse do you have for not reading what I said. I did not claim that I was offering the only definition of the word. What I said was the in the fields of evolutionary biology and paleontology the term has meaning in reference to a fossil species that shows traits from a more primitive lineage and derived lineages. You may use the word with any other definition that you wish in any context that you wish. But when you do so, you are no longer discussing evolutionary biology. Actually, I am correct. In the context of evolutionary biology and paleontology the word means what I said. I have no problem with calling such species as seals transitional. But it is a different definition of the word. Since seals are not intermediate between two lineages, they are not transitional in the sense used by evolutionary biologists.I'm saying that you can use the word in whatever context and with whatever meaning you may wish. Please don't pretend that you mean the same thing as evolutionary biologists do when they use the term. Transitional species are extinct. Transitional clades may not be. For the love of god! Wikipedia offered as a definitive source! I have actually contributed to and corrected Wikipedia on a number of topics. Sadly, what Wikipedia says and what you understand are two different things. You actually link to the page on "Transitional fossils" and chastise me for not understanding. I wonder if you actually read your own link. If you did, it is clear that you didn't understand what you read. Then I wonder why you linked the Wikipedia page about transitional fossils. What did you have in mind? Of course, since no living species has primitive traits from an earlier lineage and derived traits that are evident in subsequent lineages, no living species is transitional. They may or may not be in transition. But we don't know that. Show me a transitional species and my question is, "transitional to what?"As for the alleged confusion between transitional fossils and transitional species, I wonder who is confused. Even you attempted to explain the difference by linking a page on transitional fossils the didn't even discuss transitional species.

That's what I have been saying. Finally, I seem to have gotten through. But you did find it necessary to act like a child and try to insult me anyway. It is especially childish when in response to a question as to your intent.