Tiktaalik roseae revisited (RJS)

A couple of years ago I posted on the discovery of Tiktaalik roseae. At the time the fossil was found there were fish-like fossils dating from ca 380 mya (million years ago) and the earliest tetrapod fossil at ca. 365 mya. Thus a likely place for a transitional form between the fish-like and tetrapods was thought to be ca. 375 mya. The search that resulted in the discovery of Tiktaalik roseae is an excellent example of the way scientists seek to test evolutionary theories.

Neil Shubin and coworkers proposed to search for fossils of fresh water aquatic life forms in rock formations dating to the late Devonian era as this is the time and place where transition from lobe-finned fish to tetrapods should be found. In such a deposit they found Tiktaalik roseae. This fish had a number of features consistent with transition from lobe-finned fish to tetrapod. The find was published in Nature in back-to-back articles in 2006 (Nature, v. 440, pp. 757-763, pp. 764-771).

The story doesn’t end there though. In 2008 a second group published a more detailed study of Panderichthys and showed that this fish is even more tetrapod-like than Tiktaalik roseae (Nature v. 456, pp. 636-638). Thus Tiktaalik is not the best example of a transitional species and the transition leading from lobe-finned fish to tetrapods must have begun at least 5 or 10 million years earlier than Tiktaalik.  The Tiktaalik fossil was found when and where Shubin had predicted a transitional fossil should be found, but they could have searched in deposits representing a broader time range for new transitional forms.

Often Christians will suggest that this kind of correction and uncertainty is a basis for doubting evolution and preferring some other kind of direct creation hypothesis.

Is this kind of give and take an evidence for weakness in the evolutionary hypothesis?

Is it unexpected waffling or the expected progress of scientific discovery and the refinement of understanding?

There is even more to the story of tetrapod evolution and transitional forms. Scientists are constantly testing theories, looking for more data, refining their understanding, posing questions. In as fluid and tentative a field as tetrapod evolution nothing is taken as a given until proven. The presence of a tetrapod fossil at ca. 365 mya means that tetrapods appeared on the scene sometime before this. The presence of transitional forms in Panderichthys and Tiktaalik means that the evolutionary appearance of features leading to tetrapods began sometime before these specimen (ca. 380 mya). The gap between the transitional forms and the first tetrapod fossil was thought to be where a changeover to true tetrapods would be found. Of course the fossils set a limit on the young end, but do not establish the initial appearance of tetrapods or transitional forms between lobbed-fish and tetrapods.

In January 2010 a new paper was published by Niedźwiedzki, Szrek, Narkiewicz, Narkiewicz and Ahlberg, also in Nature (v. 463, pp. 43-48) which rocked the whole scenario again. This paper presented the findings of a tetrapod trackway dated to ca. 397 mya, pushing the date for the appearance of tetrapods back well before the date of either the Panderichthys or the Tiktaalik fossils. Tetrapod trackways are far more common than tetrapod fossils. They are used extensively to study the tetrapods in the later stages, say 330 mya or so, and palaeontologists regularly search for trackways as well as for whole body fossils.


Instead of a branch producing tetrapods at ca. 380 mya (blue-dashed line), this branch is pushed back to ca. 400 mya. Panderichthys and Tiktaalik don’t represent transitional forms between lobe-finned fish and tetrapods. Apparently they represent the continued lineage of forms transitional between lobe-finned fish and tetrapods.

Such a continued lineage is not unusual. Ancient forms can persist for very long periods. The lobe-finned fish coelacanth was believed to have gone extinct millions of years ago until a fisherman caught one 0ff the east coast of South Africa in 1938. This was called a living fossil – as ancient fossils were known long before the fish was found. The modern coelacanth is not identical to the ancient fish, but is sufficiently similar to represent a continuation of the same lineage.

The continuing saga of the dating of the appearance of tetrapods is an excellent example of the way science and scientists work. There is no “party line” that must be maintained. The data determines the consensus with much arguing and discussion along the way. New hypotheses are proposed to account for the data and new investigations undertaken to test the hypotheses. This is not evidence of a theory in trouble, but a picture of scientists and scholars at work.

What do you think?

Does this kind of investigation and revision challenge your acceptance of evolution?

Does it strengthen your confidence in the process?

If you wish to contact me directly you may do so at rjs4mail[at]att.net

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  • http://evolutionarycreation.wordpress.com EC

    I think that, for some, this could cause people to not trust what scientists say at any given point. That is, since some new discovery (new fact) could come along and force a hypothesis to change, some might think, how can I believe what the scientists say since they change their minds.

    This is, to my mind, a misunderstanding of what science is and does. Science does not bring certainty (at least not the philosophical kind). But it does provide the best explanation for the known data (at least that’s the attempt). Scientific truth does not equal certainty, and for those who think it does, or should, changing hypotheses may lead to distrust in science as a whole. I think this is groundless, but nonetheless, it can do this.

    That said, I think your example demonstrates that scientists are open to new discoveries and new hypothesis to explain the new data. In the case of evolution, new discoveries like this don’t seem to be overturning the theory as a whole. They simply point to our lack of knowledge about how exactly the lines of common descent work.

  • Brianmpei

    I think this is an example of the scientific method. I think it encourages trust in science rather than distrust. At the same time it should also give us pause whenever we hear someone speaking of things from the ancient fossil record with absolute certainty. I suppose science, like any field, has it’s fair share of egomaniacs but I think more people tend to take science pronouncements as “fact” without actually asking about the method.

    I don’t know that this specific example gives me greater confidence in the evolutionary model as much as it encourages me about the general integrity of scientific method.

  • John W Frye

    This is a good example of the process of discovery, analysis and correlation we expect in science. I agree with comment #2, though, that evolutionary scientists can be just as arrogantly dogmatic about their “facts” as some YEC are about theirs. We must proceed as scientists and theologians with a humble, chastened ‘certainty’ about what we espouse.

  • rjs

    Brianmpei,

    It is certainly common for people,including scientists, to make exaggerated claims. Ego plays a role here in science (as it does in the church at times). This can result in problems with knowing who and when to trust. I think the scientific community brings some of the “acceptance” issues down on it’s own head by overstating and overreaching.

    It is important to think hard about claims and the basis for claims. This is why I will rule out YEC as a viable explanation for the phenomena we see, but I will not rule out some form of intelligent design. I don’t think it is necessary, theologically or scientifically, but it is an area where it is best to simply commit to go with the evidence without too much significance attached.

    This story of tetrapods though isn’t an indication that evolutionary theory is in trouble.

  • JohnM

    Part of the problem is the way science is reported in the popular media. Whose fault is it when conclusions are summarized with a greater degree of certainty than is warranted? That aside, its hard not to look at this specific example as one of searching where you’ve decided you SHOULD find something you’re eager to find then, lo and behold whaddaya know, “discovering” it. Only it turns out (once again) not so much.

  • K. Reux

    It does neither for me. The truth is scientific discovery and inductive reasoning is always in a state of flux. Scientists have to approach everything with some sort of hypothesis or bias. I don’t see how anyone could do any research without some sort of bias as a foil to fence against or with.

    I am not a scientist and I am afraid I’m rather out of my depth here (pun fully intended). As I have said elsewhere, evolution (especially the non-theistic kind) is problematic to me (just from my cursory reading of micro-biology), but I am not highly analytical so I think it is essential to approach the topic with a degree of humility (which I hope I have).

    My trust is in an empty tomb, not in a particular theory of origins. If evolutionary theory is proven as fact, my faith will not be damaged. If it is shown to be impossible, it will not be a problem either.

    I think it is always best to give people the benefit of a doubt. That there are charlatans who hide their research or are blinded by their biases, there is no doubt. But I would think most scientists are honest people who love their work and are trying their best to understand the world around them.

  • Joe Canner

    JohnM #5: The way the media reports science news is not surprising (although not necessarily appropriate), given that their goal is to sell the news. “MISSING LINK FOUND!!” sells a lot better than “Fossil found on a dead-end branch that may or may not have a common ancestor with the missing link”.

    That said, both the science news reporters and the science news readers also need to be aware that science is always finding new evidence that may require modification of existing theories. In the case of tiktaalik, for example, the hype may have been somewhat justified at the time, being a creature with both fish and tetrapod characteristics. Subsequent findings showed that there is more work to be done to put the puzzle pieces together. As has been noted already, such is the nature of science: two steps forward, one step back.

  • http://krusekronicle.com Michael W. Kruse

    It always depends on the specific scientific question at hand. Some things are quite settled. Others not so much. Scientists once said the earth was round. Turns out the earth isn’t perfectly round. Does that make them wrong? To some degree, but we won’t one day be discovering that the earth is flat or cube. We might one day discover that the universe is 15 billion years old instead of about 14 billion, but we will not discover it is 10,000 years old. You can say that there are things we know with accuracy but not with precision.

    The challenge comes when science begins to interact with public policy (or conflict with religious convictions). Vested interests take on the mantle of science and certainty to shield themselves from debate … making claims of certitude on a par with evolution or the age of the earth for findings that are far from meriting such faith. It is this use and abuse of science (more typically by non-scientists than by scientists themselves) that leads to people dismissing science altogether.

  • http://thedesignspectrum.wordpress.com/ pds

    RJS,

    Sure, this is how science works. But there is more to the story. As you and others note, we need to look at how scientists talk about what we “know” at each point in the process. We also need to look at how the media presents the events to the general public.

    Did the 2010 paper get the same attention in the media as the initial reports of Tiktaalik? Of course not. And the pattern is repeated again and again, causing many of us to smile. Does the media ever focus on the well-established overall pattern of sudden appearance and stasis in the fossil record? Hardly ever.

    Does Stan Guthrie at CT have the gift of prophecy? He wrote this in 2007:

    Last year, however, came word of Tiktaalik roseae, which looks discomfitingly like those offensive “Darwin fishes” on the cars of smug college professors. Giddy evolutionists immediately hailed the 375-million-year-old fossil as a “missing link” between fish and land animals. “It’s a really amazing, remarkable intermediate fossil,” scientist Neil H. Shubin told The New York Times. “It’s like, holy cow.”

    So what’s a Doubting Thomas to do? First, we need to remember that scientists have hailed “missing links” before, only to be embarrassed when further evidence came out. The Discovery Institute, which supports Intelligent Design, noted that enthusiasm over this latest find is a backhanded admission by paleontologists that the fossil record has not been kind to Darwin’s theory.

    http://www.evolutionnews.org/2010/01/tiktaalik_blown_out_of_the_wat030621.html

  • rjs

    pds,

    I am planning to put together a post or more on the appearance/stasis observation. But I need to do it right, and haven’t had the time yet.

    None of this though is an example that the fossil record is unkind to the theory of evolutionary biology. If you define Darwin tightly by what he wrote, he has been wrong about some things – no shock here. But none of this drives us back – it brings us forward to better understanding of the process.

  • http://www.virtuphill.blospot.com phil_style

    “discomfitingly like those offensive “Darwin fishes” on the cars of smug college professors”

    I am not discomforted. I do not find them offensive. And I know not what the statistics have to say about the smugness, or profession of the people who display said “darwin fishes”, and I don’t see how Stan Guthrie could either.

    this article certainly proves the point that there’s more to a story. the stuff that journo’s come up with never ceases to amaze me.

  • rjs

    phil_style,

    I have no Darwin fish on my car … but as one of those smug(?) college professors this quote is a good example of the kind of attitude that has caused me great discomfort as a Christian and a scientist.

  • Joe Canner

    pds #9: I agree with you that it is unfortunate that the 2008 and 2010 papers did not receive as much attention as the 2006 announcement about tiktaalik. Because of the commercial nature of news reporting, as noted above, this news (“dog bites man”) does not get widely noted because it is not as interesting as the original news (“man bites dog”).

    However, I do not see how any of this has anything to do with “sudden appearance and stasis”. Please explain how any of the fish-tetrapod studies addresses this question and how any of them addresses the possible falsification of evolution as it is currently defined and understood. More to the point, if the scientists are wrong, what is the alternative explanation for the current data?

  • http://thedesignspectrum.wordpress.com/ pds

    Phil #11,

    “And I know not what the statistics have to say about the smugness, or profession of the people who display said “darwin fishes”, and I don’t see how Stan Guthrie could either.”

    Stan, get some statistics on the smugness of college professors or shut up! Unless you have statistics, you know nothing about whether college professors are smug or not.

    Seriously? Phil, did you go to college?

  • http://thedesignspectrum.wordpress.com/ pds

    Joe #13,

    That analogy doesn’t fly.

    “Fossil proves evolution” is like “dog bites man,” right? Don’t “we” already “know” that “evolution is true”?

  • http://www.virtuphill.blospot.com phil_style

    pds, surely you must realise that what I’m saying in that comment is that the writer is obviously applying rhetorical flourishes, rather than reporting hard facts in this piece. And so I stand by my comment that journalistic writing (of which that piece form a contribution) appears to have more in common with a DH Lawrence novel than it does accurate reflections of what is going on in the world.

    One only needs to look at the Telegraph’s reporting two days ago that the sale of marmite had been banned in denmark, only to find out today that it has not, to see what I’m getting at here.

  • Joe Canner

    pds #15: No single fossil, even one as interesting as tiktaalik will “prove evolution.” However, at the time, tiktaalik was an exciting find that showed a creature with both fish and tetrapod features. This is a creature that is is predicted by evolution but for which there was little evidence previously. It is a nice confirmation of one of the predictions of evolution, not a proof of evolution, but nonetheless one that was interesting enough to make it newsworthy.

  • http://thedesignspectrum.wordpress.com/ pds

    Phil #16,

    So I guess your comment was “rhetorical flourish”? :)

  • http://www.virtuphill.blospot.com phil_style

    precisely!
    This is, after all, a blog ;)

  • http://thedesignspectrum.wordpress.com/ pds

    Phil,

    For an example of “smug,” see the link below. But this goes way beyond smug, and it is even by a Christian college professor:

    http://thedesignspectrum.wordpress.com/2010/06/08/steve-matheson-to-stephen-meyer-ill-be-your-friend-you-crazy-freakish-creepy-propagandist-enemy-of-science/

  • Tim

    Great post RJS.

    I think this whole saga illustrates two aspects of important aspects of science:

    1) Science is a human enterprise. While the training scientists’ receive in proper research methodology, analysis, and critical evaluation of both their own work as well as that of their peers’ can serve to mitigate some of the typical emotional and irrational failings prevelant in human thought, it can never completely eliminate them. Issues of ego, confirmation bias, over-reaching claims, overconfidence, etc. will always exist.

    2) Science has the ability to self-correct when new evidence is presented. It can generally do so fairly rapidly, and with intellectual integrity. The outcome of the Tiktaalik situation, while embarassing to be sure, certainly highlights the exceptional ability for scientists to eat crow, accept they were wrong, and modify their view in light of new evidence. If someone wants to know what the difference between a creation “scientist” and an actual scientist, the ability to do what I just described is a big differentiator.

  • Tim

    *correction*

    I think this whole saga illustrates two important aspects of science…

  • Susan N.

    I *think* this is an example of the expected progress of scientific discovery and the refinement of understanding.

    Reading Francis Collins’ “The Language of God” currently, and have been fascinated by the science (Human Genome Project, molecular biology), as well as deeply impressed with this scientist’s humble approach to both faith in science and in God.

  • rjs

    Tim,

    The Tiktaalik saga was embarassing perhaps, but not because of the fossil itself, the search for the fossil, or the analysis of the fossil. The error was in selling it as a “missing” link rather than a transitional form setting a lower limit for the appearance of tetrapod like features. There is nothing to retract in the papers, just in the popular hype.

    But your point about egos is well taken, and doesn’t help with public credibility.

  • Tim

    RJS@24,

    I agree completely. Given the available evidence when Tiktaalik was first discovered, a claim to transitional status was certainly a warranted inference.

    I would even go so far as to say that SOME of the hype was warranted as well given its spectacular transitional features such as a neck and rudimentary wrist bones. It would be unfair, given the advantages of hindsight, to fault the scientists and authors for what really was a reasonable inference.

    However, the degree of bravado certainly went overboard. In science, well established patterns of evidence are what we really want put our credibility behind, not individual finds. In the life sciences, we have multiple lines of evidence that all converge solidly to confirm evolution/common descent. The bulk of this evidence has stood the test of time, and we do not anticipate any earth-shattering surprises. But with respect to individual finds, surprises happen all the time. So some small amount of humility with respect to Tiktaalik would have been advisable.

  • http://thedesignspectrum.wordpress.com/ pds

    RJS,

    I do appreciate you publishing this kind of post.