This November 24th marks the 150th anniversary of the publication of Charles Darwin's On the Origin of Species, one of the most important books in history. Darwin famously devoted a chapter of his magnum opus to the imperfection of the fossil record and why transitional fossils supporting his theory might prove to be difficult to find. "Missing links" do remain rare, but they are uncovered from time to time, and the most spectacular example from recent history is this month's featured animal. Famously touted for its combination of fish and tetrapod features, Tiktaalik is actually a link in a well-documented transition between lobe-finned fish such as Eusthenopteron through "fishapods" such as Panderichthys and Acanthostega to true tetrapods such as Ichthyostega. Not only is Tiktaalik an impressive fossil (or, more accurately, group of fossils, as severals pecimens have been uncovered), but it provides an excellent example of the predictive power of evolutionary theory. Chicago paleontologist Neil Shubin actually went out looking for something very like Tiktaalik; he knew the approximate age of a gap in the tetrapod fossil record, he knew that most early tetrapod fossils had been found in rocks from around the edges of the North Atlantic, and that rocks of the appropriate age (Late Devonian) outcropped on Ellesmere Island in the Candian Arctic (one of the closest major land masses to the North Pole, appropriately enough for this time of year). Shubin's hypothesis proved to be correct, and a 2004 expedition uncovered the first remains of Tiktaalik, which has since taken its place alongside Archaeopteryx and Australopithecus as one of the most impressive transitional fossils ever discovered.
