Transitional fossils: What are they?

[Pete Harcoff]

There's a phrase which many evolutionists use which for the longest time has bugged me: "All fossils are transitional fossils". It bugs me because the general definition of transitional fossil which I've come to understand is a fossil which has particular characteristics that place it as an intermediary between two other taxa.

For example, that very definition is used Index of Creationist Claims on T.O. is:

What a transitional fossil is, in keeping with what the theory of evolution predicts, is a fossil that shows a mosaic of features from an older and more recent organism.

Conversely, if a fossil does not meet this criteria then by definition it is not a transitional fossil. Hence, all fossils cannot be transitional. And indeed some fossils (i.e. trace fossils that don't show morphology at all) definitely cannot be transitional by any definition.

Compounding this, however, is the issue that the term "transitional fossil" isn't used much in scientific literature. I can't find it in any of my books on evolution and a Google Scholar search only reveals a couple hundred hits. More often, the term "missing link" is used.

I'm curious how other people define the term and how they would use it. In particular, for people who claim "all fossils are transitional fossils", can you actually defend that with a definition of transitional fossil that is all-inclusive?*

* (Although personally I feel such a definition wouldn't be terribly useful.)

 

[AV1611VET]

And indeed some fossils (i.e. trace fossils that don't show morphology at all) definitely cannot be transitional by any definition.

Just because you can't see morphing, doesn't mean it isn't a transitional.

In a conversation I had with another poster, I mentioned a dentist declaring someone 'cavity-free'; and he came back by pointing out that that doesn't necessarily mean he doesn't have any cavities.

He could indeed have cavities so small as to be undetectable by conventional instrumentation.

 

[Alunyel]

But if the fossil doesn't have those characteristics because it's too fragmentary, then how would you know?

edited to add: I started a new thread here, so we don't derail this thread further.

That would depend on whether or not you knew what the species was that the fossil was from. If it was from a species that got the short straw, and was an evolutionary dead end, then it wouldn't be a transitional fossil.

However, if the fossil is just too fragmented to be recognisable, then it's pretty useless, until technology exists that will help us identify it. At that point, it's impossible to know whether it's a fossil from a transitional species, or an evolutionary dead end.

A transitional fossil is any fossil from a transitional species. Sharing characteristics of both the next and previous stages in the evolutionary chain, but if evolution's working properly, then every fossil will share characteristics with the next and previous stages. (Except, of course, the dead ends. Infact, to make it easier, from now on, in this thread, whenever I refer to "every" fossil, I don't actually mean "every" fossil, just the ones that aren't dead ends.)

Perfect example:

Each of those skulls is in a transitional stage from the last one to the next. In turn, the next one is also in a transitional stage from the previous one, and the next.

 

[Pete Harcoff]

A transitional fossil is any fossil from a transitional species. Sharing characteristics of both the next and previous stages in the evolutionary chain, but if evolution's working properly, then every fossil will share characteristics with the next and previous stages.

So by your definition individual fossil specimens don't need to show the intermediary characteristics, just belong to a species which does.

To me this is at odds with the Talk Origins definition as given, since that definition clearly refers to individual fossils.

 

[sbvera13]

The problem is that species is nothing more then a useful label and not a hard fact of nature. Thus transitional becomes the same. It's useful when you have limited specimens of a lineage; an incomplete chain of fossils for example. Each specimen is separated by enough time to be called a different species. It's less useful when you have every intermediate step, as in the case of ring species. Then it's impossible to draw a line between species, and all individuals must be transitional.

 

[GoSeminoles!]

Imagine if someone had taken a photo of you every day of your life from birth to today. Line up the photos chronologically. It's clear that in an early photo you are an infant, in some later photo you are a gawky teenager, and in a recent photo you are an adult. But it would be nearly impossible to identify a clear demarkation line between one stage of life and the next. In which pair of photos are you a child on Monday and an adult on Tuesday?

 

[AV1611VET]

Imagine if someone had taken a photo of you every day of your life from birth to today.

More appropriately, what if, at birth, someone turned an analog camera on me with the intent of video taping my entire life, and they only had 24 hours of disk space?

 

[Sophophile]

More appropriately, what if, at birth, someone turned an analog camera on me with the intent of video taping my entire life, and they only had 24 hours of disk space?

Then the footage would end when you turned 24 hours old.

What is the point of this observation, AV1611VET?

Cheers
S.

 

[AV1611VET]

Then the footage would end when you turned 24 hours old.

What is the point of this observation, AV1611VET?

Cheers
S.

There are more mutants from abiogenesis to man than there are seconds that have elapsed.

In other words, if evolution kicked out one new mutant per second, there still wouldn't be enough time to go from the very first life --- all the way to mankind.

 

[Alunyel]

And how did you arrive at that conclusion?

The Earth is a lot older than 6000 years...

 

[The Lady Kate]

There are more mutants from abiogenesis to man than there are seconds that have elapsed.

In other words, if evolution kicked out one new mutant per second, there still wouldn't be enough time to go from the very first life --- all the way to mankind.

That would be true if we were working on a 6,000 year timeline, with a single linear progression from first life to modern life.

Fortunately, neither is the case.

 

[Pete Harcoff]

There are more mutants from abiogenesis to man than there are seconds that have elapsed.

In other words, if evolution kicked out one new mutant per second, there still wouldn't be enough time to go from the very first life --- all the way to mankind.

This thread isn't about this, so STOP DERAILING THE THREAD.

The OP is about the definition of transitional fossils and what fossils qualify. Please stick the OP or start your own thread for your own topic.

 

[Pete Harcoff]

The problem is that species is nothing more then a useful label and not a hard fact of nature. Thus transitional becomes the same. It's useful when you have limited specimens of a lineage; an incomplete chain of fossils for example. Each specimen is separated by enough time to be called a different species. It's less useful when you have every intermediate step, as in the case of ring species. Then it's impossible to draw a line between species, and all individuals must be transitional.

I agree that "transitional" is a human label.

But that's where I think the issue is the definition and how it applies. It seems to me that everyone has a different view of what a "transitional fossil" is. So some people think it's very inclusive, whereas I take the view that it's not.

This is why I'd like to focus on actually defining the term.

 

[Loudmouth]

I agree that "transitional" is a human label.

But that's where I think the issue is the definition and how it applies. It seems to me that everyone has a different view of what a "transitional fossil" is. So some people think it's very inclusive, whereas I take the view that it's not.

This is why I'd like to focus on actually defining the term.

The problem is that you can't look at a fossil and determine direct relationships. This can only be determined with DNA which happens to be lacking in most fossils. Therefore, what you are looking for is a mixture of features from two divergent taxa (e.g. Archaeopteryx has a mixture of avian and dinosaurian features). The theory of evolution predicts that such mixtures of characteristics MUST HAVE EXISTED if these evolutionary transitions occurred. Transitional fossils are evidence that these creatures did exist and that these features have been preserved in sister taxa.

"In looking for the gradations by which an organ in any species has been perfected, we ought to look exclusively to its lineal ancestors; but this is scarcely ever possible, and we are forced in each case to look to species of the same group, that is to the collateral descendants from the same original parent-form, in order to see what gradations are possible, and for the chance of some gradations having been transmitted from the earlier stages of descent, in an unaltered or little altered condition."--Charles Darwin, Origin of Species, Chapter 6

So is the platypus transitional between reptiles and placental mammals? Yes. It has a mixture of transitional features that have been preserved in it's lineage from the original parent-form. It becomes arbitrary to assign an evolutionary distance beyond which the lineage is no longer transitional. For example, there were certainly H. erectus populations that did not evolve into H. sapiens and perhaps coexisted alongside H. sapiens for a while. Does this disqualify the transitional nature of H. erectus? Not at all. H. erectus still carried transitional features even if the population from which the individual came from did not evolve into anatomically modern humans.

 

[Split Rock]

Just because you can't see morphing, doesn't mean it isn't a transitional.

In a conversation I had with another poster, I mentioned a dentist declaring someone 'cavity-free'; and he came back by pointing out that that doesn't necessarily mean he doesn't have any cavities.

He could indeed have cavities so small as to be undetectable by conventional instrumentation.

That would be me. I am honored you rembered! *shucks* However, I would remind you that was an argument that one cannot prove a negative.

 

[Pete Harcoff]

The problem is that you can't look at a fossil and determine direct relationships. This can only be determined with DNA which happens to be lacking in most fossils.

I'm not arguing about this though. I'm arguing about the specific definition of "transitional fossil".

Therefore, what you are looking for is a mixture of features from two divergent taxa (e.g. Archaeopteryx has a mixture of avian and dinosaurian features). The theory of evolution predicts that such mixtures of characteristics MUST HAVE EXISTED if these evolutionary transitions occurred. Transitional fossils are evidence that these creatures did exist and that these features have been preserved in sister taxa.

Right, this is what I'm driving at. BUT, if you had a framentary fossil of a transitional species, but the individual fossil itself lacked the transitional characteristics (i.e. it's too incomplete), would that individual fossil qualify as a "transitional fossil"?

My view is that no it wouldn't.

 

[metherion]

Right, this is what I'm driving at. BUT, if you had a framentary fossil of a transitional species, but the individual fossil itself lacked the transitional characteristics (i.e. it's too incomplete), would that individual fossil qualify as a "transitional fossil"?

My view is that no it wouldn't.

So, just for my own understanding, you could have two fossils from the same transitional species (we will say it is just for the purposes of this statement, but that might be a whole 'nother bucket o worms) and if one fossil shows the parts decided to be transitional while the other is damaged and doesn't, one will be transitional, and the other won't.

Like if species X had a clear transition around frontal limb characteristics, say, fins to forelimbs. If fossil A was of this species and only contained the spine and the skull, while fossil B contained the spine, skull, AND forelimbs in question, B would be transitional, but A would not, despite being from the same species. Correct?

Metherion

 

[tanzanos]

Just because you can't see morphing, doesn't mean it isn't a transitional.

In a conversation I had with another poster, I mentioned a dentist declaring someone 'cavity-free'; and he came back by pointing out that that doesn't necessarily mean he doesn't have any cavities.

He could indeed have cavities so small as to be undetectable by conventional instrumentation.

Good Lord AV! Have you gone to the other side? You are confusing me! Your posts lately seem to have valid points!

Ahhh I get it. You're just messing with us, Ya?

 

[Loudmouth]

Right, this is what I'm driving at. BUT, if you had a framentary fossil of a transitional species, but the individual fossil itself lacked the transitional characteristics (i.e. it's too incomplete), would that individual fossil qualify as a "transitional fossil"?

My view is that no it wouldn't.

I would agree. I used to go fossil hunting near the Snake River in Idaho. I found a lot of rib bones and single vertebrae from ancient fish. I would hardly call these transitional fossils. Also, by definition the fossil needs to have a mosaic of features from two divergent taxa. No mosaic, no transitional.

 

[Aggie]

That would depend on whether or not you knew what the species was that the fossil was from. If it was from a species that got the short straw, and was an evolutionary dead end, then it wouldn't be a transitional fossil.

Loudmouth sort of pointed this out already, but we can almost never know whether or not this is the case. So for example, Archaeopteryx could have been a direct ancestor to all modern birds, but it’s equally possible that it was an evolutionary dead end and that birds are descended from some earlier, similar group of animals. But even if that were the case, it wouldn’t take away Archaeopteryx’s status as a transitional fossil, because it demonstrates an anatomical intermediate between dinosaurs and birds regardless of whether it was a direct ancestor to birds or not.

There are also some fossils that are considered transitional even though they were almost certainly evolutionary dead ends, such as most of the feathered dinosaur fossils. Around 90% of them are from rocks more recent than Archaeopteryx, which means that they could not have been direct ancestors of birds. But since they show anatomical intermediates between dinosaurs and birds, and are something specifically predicted by the theory of evolution, they’re still considered transitional fossils.