One of the best-documented evolutionary transitions is the appearance of tetrapods, the four-limbed vertebrates that now dominate the land. A large series of "fishapod" fossils have been discovered that reveal animals that were clearly fish, but had increasingly complex fins and other features of tetrapods (such as a distinct neck). The most famous of these is probably Tiktaalik roseae, which was found by searching deposits that date from the time of this transition.

There was just one awkward problem with this picture: preserved trackways showed that something was walking around on the bottom of rivers millions of years before animals like Tiktaalik. But researchers have now provided an explanation for this discrepancy, as they show that the lungfish, a living relative of the tetrapods ancestors, uses its fins to walk across river bottoms, leaving behind tracks that look like those of early tetrapods. And they discovered this by an extremely simple research method: they watched the fish.

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