Word: tetrapod
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...cage, suggesting that it had lungs and did at least part of its breathing through them, as well as a trunk strong enough to support itself in the shallows or on land. And most startling of all, when technicians dissected its pectoral fins, they found the beginnings of a tetrapod hand, complete with a primitive version of a wrist and five fingerlike bones. "This is not some archaic branch of the animal kingdom," says Shubin. "This is our branch. You're looking at your great-great-great-great cousin...
Together, these fossils have overturned the old picture of the fish-tetrapod transition, which conjured up the image of creatures like the modern lungfish crawling out of water onto land. That picture certainly didn't fit Acanthostega, whose short, flimsy legs were ill equipped for terrestrial locomotion. Rather, according to University of Cambridge paleontologist Jennifer Clack, Acanthostega was an aquatic creature that used its limbs and lungs to make a living in water. And that scenario makes sense because it sets up conditions for natural selection--the force that powers evolution--to favor transitional life-forms like the fishapod, with...
...Shubin, University of Chicago 380 million years ago BEFORE TIKTAALIK Lobe-finned fish had forelimbs suitable for moving in water but not on land 375 million years ago TIKTAALIK The forelimbs had the beginnings of fingers and a wrist, wrapped inside a fin 360 million years ago AFTER TIKTAALIK Tetrapod forelimbs have wrists and digits used for crawling on land [This article consists of a complex illustration. Please see hardcopy of magazine...
...fills a gap in our understanding,” Jenkins said. “We knew about lobed-fin fish, we knew about early tetrapods, but how do you turn lobed-fin fish into tetrapods? This fish is beginning to turn into a tetrapod, giving us real insight on anatomical evolutionary transformation...
...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 it through the water...