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Tiktaalik roseae and Friends (RJS)

Tiktaalik roseae and Friends (RJS)

Last updated on: February 6, 2013 at 7:47 pm by RJS

Tiktaalik roseae and Friends (RJS) 2013-02-06T19:47:00-06:00 RJS

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Nay, fly to Altars; there they’ll talk you dead;

For Fools rush in where Angels fear to tread.

The Fool referred to by Alexander Pope was the literary critic of his day. Fear not – I intend no literary criticism. Yet the famous quote reflects something of the trepidation I feel as I rush in to tackle a somewhat controversial issue – evolution, the fossil record, and transitional forms (missing links) – and the way we as Christians approach the data. Here we go.

One of the issues raised by Darwin’s theory of evolution was the presence – or more accurately the absence – of transitional forms in the fossil record. The fragmentary nature of the fossil record has been a common criticism by those who doubt if evolution explains the development of life. Because such fossils can provide a line of evidence for the validity of the theory and also provide important insight into the mechanism of evolution these forms are both sought and, when found, publicized and criticized. One of the most interesting finds of recent years is Tiktaalik roseae, reported by Neil Shubin, Ted Daeschler, and Farish A. Jenkins, Jr. in back to back Nature articles in 2006. Their website gives references and details (here) and the National Science Foundation press release is found here.

I am convinced that as a church how we approach the data and how we handle the controversy is just as important as, if not more important than, the final conclusions we draw. As we look a bit at this discovery and its interpretation I would like to consider two questions.

What do you make of such fossil finds? On what do you base your opinion?

How does our approach affect the attitude our students take to high school and college regarding the conflict or coherence between science and faith?

Before I continue a disclaimer: The fields of evolutionary biology and paleontology both fall outside my areas of personal expertise. I will be happy to correct any errors of fact (or grammar) once verified.

Tiktaalik roseae: The search that resulted in the discovery of Tiktaalik roseae is an excellent example of the way scientists seek to test evolutionary theories. The investigators proposed to several funding agencies including the National Science Foundation that it would be useful 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. Their peer-reviewed proposals were funded and the search was on.

An appropriate Devonian freshwater deposit was identified in the Canadian arctic above the arctic circle and expeditions were arranged to search this heretofore unexplored site. In 2000 they found a site with interesting fish and in 2004 they found specimens of a new fossil which they named Tiktaalik roseae. Their first two papers reporting the discovery were submitted in October 2005 and published in 2006.

In the first paper the investigators highlighted a number of transitional features in Tiktaalik. This “fish” is thought to have occupied shallow marshy waters. In support of this interpretation they noted that “ribs of the type that occur in Tiktaalik augment thoracolumbar rigidity and axial support, functions that are not necessary in an aquatic setting that is deep enough to support the body.” (Nature, 440, pp. 757-763) That is – Tiktaalik had a well developed strong rib cage. Such a rib cage is necessary when the body is supported by limbs, it is unnecessary in a deep water fish. There are other transitional features identified in the neck, head, and respiratory structures.

In the second paper the authors discussed the limbs and digits of the fossil. Tiktaalik roseae exhibits bones and joints in the fin that are similar to the limb pattern of tetrapods. The authors suggest that the origin of limbs in tetrapods likely developed through “the elaboration and proliferation of features already present in the fins of fish such as Tiktaalik.” (Nature, 440, pp. 764-771).

Panderichthys: This fossil, also from the Late Devonian era, but somewhat earlier than Tiktaalik (see chart above) has been known for awhile, but most studies were on fragmentary specimens. New technology permitted study of intact specimens incased in rock. In the fall of 2008 a paper was published in Nature (Nature 456, 636-638) reporting the results of these studies. The Swedish group of Catherine A. Boisvert, Elga Mark-Kurik and Per E. Ahlberg reported that their observations demonstrated that the appendages of Panderichthys are more tetrapod-like than those of Tiktaalik. From the paper:

Here we present a CT scan study of an undisturbed pectoral fin of Panderichthys demonstrating that the plate-like ‘ulnare’ of previous reconstructions is an artefact and that distal radials are in fact present. This distal portion is more tetrapod-like than that found in Tiktaalik and, in combination with new data about fin development in basal actinopterygians, sharks and lungfish, makes a strong case for fingers not being a novelty of tetrapods but derived from pre-existing distal radials present in all sarcopterygian fish. (p. 636)

So what do fossils such as Panderichthys and Tiktaalik suggest about the transition from sea to land and about the evolution of digits? An interesting article was published recently in Science News entitled Step-by-step Evolution Mining the Gaps: Transitional fossils are the hardest to find, but sometimes tell the best stories.

One of the points made in this story (and in the original articles, including Boisvert’s Nature paper) is that it was thought that “Panderichthys and the lobe-finned fish of their era didn’t reveal bony features in the fins. Scientists interpreted this lack as a sign that digits were an evolutionary novelty that only arose later in land-adapted creatures.” However, Tiktaalik, the new CT scans of intact Panderichthys, and a number of other studies now suggest that “all that evolution did was reshape and repattern a structure that was already there…. It didn’t have to build a novel extension of the body from scratch, so the transition from fish to land vertebrate becomes a little less dramatic than we thought it was.“

If I interpret these studies correctly the gene (HOX) that leads to the formation of digits was already present in the lob-finned fish – its expression changed in the process of movement from sea to land – and perhaps changed at different times in different ways in different species. I don’t think that these kinds of timing differences are unusual. It is not significant for the overall hypothesis of evolution from fish to tetrapod that the digits of Panderichthys are better developed than those of Tiktaalik.

Do these studies prove evolution? My intent here is not to prove evolution, but rather to lay out some small portion of the evidence. To do so I looked at the primary literature and at some secondary literature. None of these specimens, Tiktaalik,
Panderichthys, or any of the others alone “prove” evolution and common descent. When all of the evidence is taken together however, it is quite persuasive. I certainly think that the general evolutionary paradigm is strongly supported by the evidence. Perhaps some other explanation accounting for all of the evidence is forthcoming – but I rather doubt it.

These two fossils have become something of a case study in how the data is used by those who wish to cast doubt on the theories of evolution. The results reported by Boisert et al. on Panderichthys received heavy coverage in the general press and were used (see the article here: http://www.evolutionnews.org/2008/09/the_rise_and_fall_of_tiktaalik.html) to suggest that the “discrepancy” between Panderichthys and Tiktaalik was a serious blow to evolutionary theories and to the status of Tiktaalik as transitional between fish and land-based tetrapods. The very title of the ENV article is worth note: The Rise and Fall of Tiktaalik? Darwinists Admit “Quality” of Evolutionary Icon is “Poor” in Retroactive Confession of Ignorance. Among other things the Evolution News and Views article states:

The “quality” of Tiktaalik as a fossil specimen was “poor”? When did we see Darwinists admit this previously? Never. They wouldn’t dare make such admissions until they thought they had something better.

Unfortunately this statement is based on neither the original papers nor the actual condition of the fossils. On top of this the evidence from digit development is only one of the transitional feature of Tiktaalik. The new data has refined understanding of the development of digits – but this is the way science normally operates as ideas are tested and refined in the light of new evidence.

Catherine Boisvert was interviewed on a blog here about her reaction to the way her statements and paper were being interpreted.

AFM: The creationist Discovery Institute has pounced on some of the statements in your paper regarding sample quality as evidence that scientists are trying to backpedal on previous hypotheses regarding digit development and evolution. Can you clarify your statements regarding sample quality of Tiktaalik and Panderichthys?

CB: As you know, the “Discovery” Institute tactic is not to go to the primary literature in order to understand it but rather to use quotations from secondary, even tertiary sources, reorganise or use them out of context opportunistically to their own convenience. In this case, they used an article where the journalists unfortunately
misunderstood me. Tiktaalik‘s material is in fact exquisite, it is very well preserved, basically uncrushed and can be prepared out to be examined in three dimensions. I never said the quality was poor. I have simply explained that the morphology of the fin of Panderichthys is more tetrapod-like than that of Tiktaalik, which has nothing to do with the quality of the material.

We must be honest with people and with the data – and we must do our homework. It does no good to criticize the evidence for evolution without taking the available data seriously, and dealing with it honestly. Failure to do so will result in an unnecessary crisis of faith for far too many of our high school and college students, and especially for those who continue their training beyond the college level in the biological and physical sciences. One of the commenters on the post Darwin and the Bible 3 last Tuesday noted:

In my opinion, much of the turmoil was fostered by the small army of Christian writers (every denomination has them) that write so confidently regarding the evils of biological evolution (or more naively “Darwinism”) and yet understand very little about where the scientific field is today. … Therefore, much of the ‘turmoil’ resulted from what I perceived as intellectual dishonesty from my Christian brothers or sisters.

I couldn’t put it any better – failure to deal with the data with integrity is disaster. My assessment of the data leads me to take the position that God used evolutionary mechanisms as his means of creation.

Whether you agree with me or not – what approach should we take to understanding and discussing all of the evidence and issues in the debate over evolution and creation? How can we best prepare our youth for the challenges ahead?

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

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