Word: fishelis
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About 360 million years ago, as any schoolchild who knows his prehistoric zoology can tell you, some adventurous fish managed to hoist themselves onto their stubby fins and crawl clumsily out of the swamps to forage for food. Once these primeval creatures were on terra firma, their offspring began to adapt to their new environment, natural selection (over tens of millions of years) favoring those that developed features well suited to life on land: paws, hooves, knees, joints, fingers and thumbs. Thus, as generations of schoolchildren have learned, did these marine creatures give rise to frogs, birds, dinosaurs...
...fossils -- in particular, a 360 million-year-old salamander-like aquatic animal called Acanthostega -- strongly suggest that toes and feet were developed before life climbed onto land, not after. Moreover, in shape and function, Acanthostega's fully jointed toes bear no resemblance to the spiky, fanlike fins of a fish. Scientists believe they understand how a fish's gills evolved into an amphibian's lungs. But how did fins turn into feet like these...
...answer may be in the genes. That's the tantalizing conclusion of a team of researchers from the University of Geneva in Switzerland. They have discovered that genes associated with the formation of fins in fish are the same ones that orchestrate the development of paws in mice. "Think of a mouse as a fish with limbs, or a fish as a mouse with fins," says University of Geneva developmental biologist Denis Duboule. "What a mouse does is take a fin and put something extra...
What would a fish with feet look like? It could easily resemble the Acanthostega. Mineralized bones of this strange creature, unearthed in Greenland in 1987, tend to confirm the notion that fish did not crawl onto shores on their fins, says paleontologist Michael Coates of University College, London. Instead they probably developed limbs and feet that they used in the water for millions of years before they were capable of colonizing the land...
...transition to land was likely a gradual affair involving multiple stages of evolutionary change. The skeletons of fish, with their slender bones arrayed all in a row, are clearly ill suited for walking and running. Moreover, the muscles of fish are designed to deliver power in all the wrong places. "Think about tucking into a tetrapod [a cow, for instance] for Sunday lunch," says Coates. "The best cuts are the thighs and shoulders, the muscle motors that drive these animals along. In a fish these motors are pathetic, tiny things. It's the back and tail muscles that propel...