Fair enough, so they were aware of it. Yet the problem persists and those types variations are still read as separate species until somebody attempts to prove otherwise. Horner himself admits that paleontologists are eager to say they've discovered a new type of animal at the expense of consideration for the issue in question. So the real question is how many dinosaurs are misidentified? Any idea?
Excellent. So let's hear no more talk of how shocked paleontologists are by Horner's research.
As for your question, I would say many are probably misidentified, but most aren't. There are approximately
1339 species of dinosaur recognized at the moment. Breaking it down
stratigraphically.
So we know that the 866 Cretaceous species are not the same as the 473 species separated stratigraphically therefrom, and the same logic holds for the other two periods. Looking at the Cretaceous in detail (because it is the most speciose), we see a bunch of species that are again separated stratigraphically and are not therefore conspecific. Now let's look at the
Campanian in detail, again because it is most speciose.
*Note: all these numbers are somewhat approximate due to vagaries of the PBDB
EDITED to correct mysterious formatting nonsense by linked using images instead.
We can see that the 259 Campanian species are separated pretty well geographically which is a good indication that they aren't conspecifics.
So by simply looking at stratigraphic and geographic segregation, we can see that a substantial portion of the species named are most likely not the same. And then of course there are the finer resolution studies, of which Horner's and Dodson's are just a couple examples, that look at the ontogeny of a certain genus or family, further narrowing the number of taxa that have been incorrectly identified.
So while I can't tell you specifically how many species have been erected in error, I can say that the majority of species are probably not the same species under different names.
Well these are also the types of variations that are typically read as (and used as evidence for) "evolutionary" progressions, since major body-plan transitions do not exist save a few extremely ambiguous examples.
Could you clarify the point you're making here?
Okay, but I still don't see how the same potential problems with dinosaurs doesn't transfer over to other extinct groups like synapsids, the problem being that ontological variation is not always rigorously tested for and may have caused misidentification. Saying "it is possible to asses it" does not mean it is always assessed.
You would not be mistaken in suggesting that the same problem applies to other fossil taxa, although as I have said the literature suggests that the extreme ontogenetic variation seen in dinosaurs is not typical of most taxa. I agree that just because this variation can be detected doesn't necessarily mean it will be, but a lot of paleontologists actually have little to no interest in dinosaurs and there is in fact a great deal of research specifically into the life histories of a wide variety of non-dinosaurian taxa.
Your strawman was that I claimed no ontological variation is ever studied in anything.
That is indeed quite a strawman. But I feel confident in guaranteeing that you will be unable to produce a quote from me that argues against that rather than your quoted belief that ontogenetic variation has only been studied recently and that Horner's research was a shocking "revelation".
I do concede that the problem has been known for longer than I thought, but this really doesn't change anything. Scientists are still being fooled by it. How many more misidentified animals are there? I don't understand how you can claim an unknown factor is a negligible one.
Good to hear. But I don't see your justification for saying it doesn't change anything. You seem to have clipped this part of my post that addresses this claim:
It certainly does diminish the consequences. It obviously doesn't mean that the problem is solved, but having been actively studying the issue of ontogenetic variation in dinosaurs for decades means that there are much fewer erroneously-identified species than there would be if paleontologists had just recently realized such errors could be made. For instance, Dodson (1975) alone identified nine "species" of lambeosaur that were ontogenetic morphs of two or three genera.
I'm not claiming it is a negligible source of error to be ignored, I'm saying it has been and continues to be heavily studied and that, while errors are still made, such studies allow these and past errors to be corrected.
Are you referring to this one study you linked to on Plateosarus?
http://www.ncbi.nlm.nih.gov/pubmed/16357257
That's the one
I never claimed phenotypic plasticity is not studied at all in dinosaurs. This is the same thing as ontology. You're trying to argue that the mere fact that it is studied "removes the possibility that it is causing classification errors.
That is not my argument. My argument is that the research into plasticity and ontogeny have furnished us with the ability to detect them well enough in the fossil record to correct and avoid many possible errors and that we are therefore justified in making conclusions based on the fossil record. This is not the same as saying that the study of the these two sources of intraspecific variation "removes the possibility that it is causing classification errors".
I agree. When they're looking for it and when there is a broad enough sample base to make comparisons. "Transitional" sequences are often made up of very sparse amount of partial fossil samples.
Excellent. Though I should point out that our ability to assess approximate age (juvenile, subadult, adult) histologically is sufficiently advanced that we don't necessarily need a large sample size to identify, say, juvenile bone structure.
It's not well-enough understood in living animals that have been studied closely for decades. It's quite logical to assume that it is not well-enough understood from the fossil remains of extinct taxa.
It is logical to assume that there is more to learn about the phenomenon. It is not well-founded to assume that, because our knowledge is incomplete, paleontologists are not capable of making reliable assessments of its presence in the fossil record and are therefore not capable of making reliable assessments based on the fossil record.
That wasn't what I was arguing. It was an example of a level of plasticity that was not expected, and was initially interpreted as the "evolution" of novel traits.
I know that's not what you were arguing. It is a point I was making.
The cecal valves completely disappeared in only 15 weeks. This is a trait that was previously identified as the product of "evolution" (i.e. mutation and selection over a long period of time)
This doesn't address the point that neither the skull in general nor the teeth in particular displayed plasticity by changing in response to diet and that the fact that even these minor osteological differences did not change suggests that the suite of far more noticeable changes to cranial morphology between
T. horridus and
T. prorsus is beyond the limits of plasticity.
It would be interesting to study the reverse plasticity experiment and see what happens to the skulls and teeth going from insect to plant where those changes would be more important for adapting to tougher material. How much do you want to bet they are relatively similarly timed plastic responses associated with appearance of the cecal valves?
It would be interesting to carry out such a study, but your personal confidence that your prediction would be vindicated is hardly to be considered support for your position.
The studies are very short-term and only looking at very specific stimuli. It amazes me that you so readily see these limits, yet you think adding a couple hundred million years will produce a man from a fish.
Plasticity, as has been noted in the research presented here, is capable of limited change, generally below what we observe between species. It is but a small part of the greater possibilities for change associated with evolutionary processes.
And you got the answer: Yes. Horner, as a paleontologist who has studied bone histology for several decades, is certainly aware of the issue of plasticity. In fact if you can find that
Plateosaurus paper cited in his research.
In other words, you're basing your conclusion off the assumption that the strata represent millions of years.
That's a whole other thread. But I would point out that your assumption that
T. horridus and
T. prorsus were actually coeval makes little sense when we consider that that occupy the same ecological and geographical setting and yet the latter species is only found in the upper third of the HCF with a series of decreasingly
prorsus-like specimens below it. You have in the past suggested that somehow various microcurrents transported similar organisms with similar ecologies form similar locations to exclusively separate strata, but this both unsupported and unlikely. That fact that your sorting mechanism would also have had to account for the gradual character shift between the two species makes it particularly absurd.
Plasticity would not have to play a role at all in the case of reproductive isolation. You certainly don't know that they occupied the same geographic area without first assuming the strata represent intact geographical areas to begin with, where the animals died instead of being transported there in sediments.
This doesn't address the argument that reproductive isolation would produce the gradual divergence of two morphs rather than the gradual shift from one taxon to another. Again your issues with the geological record seem like too large a topic to be considered in this thread, or at least this discussion.
The hypothesis that they are different 'breeds' of the same species still has far more observational support than the mysterious idea that the animals were "evolving" new traits.
Mere rhetoric and highly subjective. Again, how is the gradual acquisition of a suite of traits by one taxon until it is sufficiently different to be classified as a separate species not evidence of evolution? You've already made it clear that you think that fairly minor changes are capable of adding up to produce major change over a long enough time scale. You just refuse to ascribe the change to evolutionary processes.
Sorry have not had enough time.
Cool. Just reminding you.
