This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Friends and colleagues who know that I illustrated Neil Shubin's first book, Your Inner Fish, have been asking if I was involved in the three-part PBS series hosted by Shubin that will air next week on April 9th. The short answer is no. But I'm proud to say that I made this very model of Tiktaalik's fin that Shubin is holding in his PBS preview:
When I built the model shortly after we pulled the fin bones from the rock, I had no idea it would get so much airtime, so to speak. It was really just a model for us to understand the range of movement of the fin. But this model has shown more people how illuminating Tiktaalik is than perhaps anything I made while in Shubin's lab. For fun, I thought I'd walk you through a behind-the-scenes tour of how it came to be.
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Tiktaalik is special for many reasons, but one of the most notable is because it is so spectacularly preserved. To become a fossil, first you have to die without being eaten and scattered across the plains. Then you must be buried in sediments that will prevent you from totally disintegrating. Then get ready to endure mind-numbing pressures and temperatures that will bake you into rock, but not completely incinerate you. If you've made it this far, congratulations, you're a fossil (can somebody please ask Warren Buffett to calculate the odds of any one of us fossilizing? He might risk his entire fortune on that one...) Is it any wonder that most fossils are crushed and flattened and generally incomplete skeletons?
Incredibly, many specimens representing Tiktaalik's species survived the fossil-making process intact and managed the additional feat of being found by scientists who postulated their existence. And lucky me, I got to draw and reconstruct Tiktaalik's fin based on these remarkable, three-dimensional specimens. I tell you this because most people look at the model Shubin is holding and think it just sprung from the earth as is (it didn't). In reality, it is a combination of actual replicas of the bones from one individual and carefully sculpted pieces that I made based on other specimens.
I already mentioned Tiktaalik is special because it is preserved exceptionally well. The best specimen we have is the one you may have seen pictures of. It graced the cover of The New York Times on the day that the two papers appeared in Nature announcing the discovery:
This is the most complete specimen of Tiktaalik we have, but it is not the biggest, nor is it the best for understanding structures like the fin. There are a number of other specimens that shed light on the fin in ways that eventually led to the reconstruction you see in the preview above. First, there is a three-dimensional fin and shoulder that looks like it was hauled out of the river yesterday:
Another is an isolated shoulder from a smaller individual that is preserved perfectly in three dimensions:
Finally, the largest specimen of Tiktaalik provided the opportunity to pull out each of the fin bones in isolation to see how they fit together. From this individual, we had bones from both the right and left fins, but not a complete set from either side. We knew from the other specimens, though, which pieces went where so we could be completely confident about the final reconstruction.
From these three sources, I made a composite fin using casts of the original bones from the largest specimen and carefully sculpted pieces informed by all three specimens. Although the shoulder of the large specimen was flattened to pancake status, we had a perfect model from a smaller specimen, so I sculpted a "reinflated" version of the pancaked shoulder that would fit the rest of the large fin. And for the smallest bones at the end of the fin that were too fragile to be completely removed from the rock, I sculpted simple approximations of those bones as though we had pulled them from the rock in 3D. Finally, I drilled a few holes and connected the bones using wire and foam joint pads and voila: a bendable, composite reconstruction of three Tiktaalik specimens.
