Once again, the Discovery Institute stumbles all over itself to crow victory over evolution, led by the inspiring figure of that squeaking incompetent, Casey Luskin. This time, what has them declaring the bankruptcy of evolution is the discovery of tetrapod trackways in Poland dating back 395 million years. I know, it’s peculiar; every time a scientist finds something new and exciting about our evolutionary history, the bozos at the DI rush in to announce that it means the demise of Darwinism. Luskin has become the Baghdad Bob of creationism.
The grounds for this announcement is the bizarre idea that somehow, older footprints invalidate the status of Tiktaalik as a transitional form, making all the excitement about that fossil erroneous. As we’ve come to expect, though, all it really tells us is that Casey Luskin didn’t comprehend the original announcement about Tiktaalik, and still doesn’t understand what was discovered in Poland.
The fossil tetrapod footprints indicate Tiktaalik came over 10 million years after the existence of the first known true tetrapod. Tiktaalik, of course, is not a tetrapod but a fish, and these footprints make it very difficult to presently argue that Tiktaalik is a transitional link between fish and tetrapods. It’s not a “snapshot of fish evolving into land animals,” because if this transition ever took place it seems to have occurred millions of years before Tiktaalik.
Errm, no. Shubin and Daeschler are smart guys who understand what fossils tell us, and they never, ever argued that Tiktaalik‘s status as a transitional form depended on slotting it in precisely in a specific chronological time period as a ‘link’ between two stages in the evolution of a lineage. A fossil is representative of a range of individuals that existed over a window of time; a window that might be quite wide. They would never express the kind of simplistic, naive view of the relationship of a fossil that the DI clowns seem to have. For instance, here’s a picture of the relationship between various fossils, as published in Nature when Tiktaalik was announced.
The lineage leading to modern tetrapods includes several fossil animals that form a morphological bridge between fishes and tetrapods. Five of the most completely known are the osteolepiform Eusthenopteron; the transitional forms Panderichthys and Tiktaalik; and the primitive tetrapods Acanthostega and Ichthyostega. The vertebral column of Panderichthys is poorly known and not shown. The skull roofs (left) show the loss of the gill cover (blue), reduction in size of the postparietal bones (green) and gradual reshaping of the skull. The transitional zone (red) bounded by Panderichthys and Tiktaalik can now be characterized in detail. These drawings are not to scale, but all animals are between 75 cm and 1.5 m in length. They are all Middle–Late Devonian in age, ranging from 385 million years (Panderichthys) to 365 million years (Acanthostega, Ichthyostega). The Devonian–Carboniferous boundary is dated to 359 million years ago.
Notice what you don’t see? They didn’t publish this as a direct, linear relationship that could be disrupted by a minor anachronism. It does not look like this:
Ichthyostega
↑
Acanthostega
↑
Tiktaalik
↑
Panderichthys
↑
Eusthenopteron
↑
These are all cousins branching off the main stem that led to modern tetrapods. Tiktaalik was almost certainly not our direct ancestor, but a distant cousin that was representative of a transitional state in the branching cloud of species that emerged out of the Devonian. And the authors of these papers knew that all along, weren’t shy about stating it, and if they made an error about anything, it would be in assuming that a gang of self-styled scholars who claim to be presenting a serious rebuttal to evolutionary ideas would actually already understand a basic concept in paleontology.
You would think Luskin would have also read the Niedzwiedzki paper that describes this new trackway, which rather clearly describes the implications of the discovery. It does not declare Tiktaalik to be uninteresting, irrelevant to understanding the transition between fish and tetrapods, or that Tiktaalik is no longer a transitional form. It clearly is.
No, here’s the new picture of tetrapod evolution that Niedzwiedzki and others have drawn. At the top is a diagram of the relationships as understood before the discovery, at the bottom is the new order.
Phylogenetic implications of tracks. a, Phylogeny of selected elpistostegids and stem tetrapods fitted to Devonian stratigraphy. The grey bar indicates replacement of elpistostegids by tetrapods in body fossil record. b, Effect of adding the ZacheÅmie tracks to the phylogeny: the ghost ranges of tetrapods and elpistostegids are greatly extended and the ‘changeover’ is revealed to be an artefact. Pan, Panderichthys; Tik, Tiktaalik; Elp, Elpistostege; Liv, Livoniana; Elg, Elginerpeton; Ven, Ventastega; Met, Metaxygnathus; Aca, Acanthostega; Ich, Ichthyostega; Tul, Tulerpeton. ANSP 21350 is an unnamed humerus described in ref 17. The bars are approximate measures of the uncertainty of dating. These are not statistical error bars but an attempt to reflect ongoing debate.
Look closely.
Hey, the branches are the same! The relationships are unchanged! What has changed is that the branches of the tree go back deeper in time, and rather than a sharp changeover, there was a more prolonged period of history in which, clearly, fish, fishapods, and tetrapods coexisted, which isn’t surprising at all. Tetrapod evolution was spread out over a longer period of time than was previously thought, but this is simply a quantitative shift, not a qualitative change in our understanding of the relationships of these animals. It also says that there is the potential for many more fossils out there over a bigger spread of time than was expected, which is something we can look forward to in future research. Not research from the Discovery Institute, of course. Research from real scientists.
Now also, please look at the b phylogeny above, and tell me where the evidence for Intelligent Design creationism in this new figure lies. Perhaps you can see how a cladogram illustrating the evolutionary relationships between a number of fossils challenges our understanding of evolutionary history, because I don’t see it. If anything, it affirms the evolution, not the Sudden Appearance by Divine Fiat, of tetrapods.
For extra credit, explain where in diagram b of the Niedzwiedzki paper it shows that Tiktaalik has been “blown out of the water,” as Luskin puts it. Should they have scribbled in a frowny face or a skull and dagger next to the Tiktaalik bar, or perhaps have drawn a big red “X” over it? Because I can guarantee you that Niedzwiedzki and coauthors still consider Tiktaalik a transitional form that is part of the story of tetrapod evolution. All they’ve done is put it on the end of a longer branch. Nothing has changed; Tiktaalik is still a revealing fossil that shows how certain vertebrates switched from fins to limbs.
Finally, just for fun, maybe you can try to explain how the “Big Tent” of Intelligent Design creationism is going to explain how the Young Earth creationists in their camp — you know, the ones that think the planet is less than ten thousand years old — are going to find it heartening that a fossil discovery has pushed one stage in tetrapod evolution back farther by another 20 million years. That’s 2 x 103 times greater than the entire span of time they allow for the existence of the universe, all spent in shaping a fin into a foot. There ought to be some feeble expression of cognitive dissonance out of that crowd, but I suspect they won’t even notice; as Luskin shows, they aren’t particularly deep thinkers.
Ahlberg PE, Clack JA (2006) A firm step from water to land. Nature 440:747-749.
Daeschler EB, Shubin NH, Jenkins FA (2006) A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature 440:757-763.
Niedzwiedzki G, Szrek P, Narkiewicz K, Narkiewicz M, Ahlberg PE (2010) Tetrapod trackways from the early Middle Devonian period of Poland. Nature 463(7277): 43-48.
Shubin NH, Daeschler EB, Jenkins FA (2006) The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb. Nature 440:764-771.
