The evolution of tetrapods

The December issue of Scientific American has an excellent article by Jennifer Clack on the evolution of tetrapods (four-limbed vertebrates; aka, us). I was pondering summarizing the article here, but I just checked Scientific American's website and they've got the entire thing available for free. So, head over there and read it.

In brief, the article attempts to reconstruct the events surrounding the evolution of air-breathing tetrapod vertebrates 380 million to 375 million years ago, basing most of its conclusions on recently discovered fossils. I'll post a short bit from the article as a teaser:

With such scant clues to work from, scientists could only speculate about the nature of the transition [from fish to tetrapod]. Perhaps the best known of the scenarios produced by this guesswork was that championed by famed vertebrate paleontologist Alfred Sherwood Romer of Harvard University, who proposed in the 1950s that fish like Eusthenopteron, stranded under arid conditions, used their muscular appendages to drag themselves to a new body of water. Over time, so the idea went, those fish able to cover more ground--and thus reach ever more distant water sources--were selected for, eventually leading to the origin of true limbs. In other words, fish came out of the water before they evolved legs.

Since then, however, many more fossils documenting this transformation have come to light. These discoveries have expanded almost exponentially our understanding of this critical chapter in the history of life on earth--and turned old notions about early tetrapod evolution, diversity, biogeography and paleoecology on their heads.