For markers of a mass extinction, the fossils dug up from the Namibian soil are not very impressive. The few animals caught in the rock are ribbon-shaped and worm-like. Many are nothing but impressions in 540-million-year-old sea bed muck, tunnels left behind by burrowing creatures whose soft bodies were not preserved. Others are small craters that erupt out of the ancient sand like exploded zits. The scientists studying these fossil traces say the indentations could not have been left by bubbling gas — where gas would leave a pointed impression like a volcano, these holes are concave — but are where predatory sea anemones once anchored themselves to the sea floor. If this fossil trove had a ...
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