GEORGE BERNARD / SCIENCE PHOTO LIBRARY GEORGE BERNARD / SCIENCE PHOTO LIBRARY
Fossil coral. Polished surface of rock containing fossilized rugose coral, Lonsdaleia caledonia. This species, now extinct, lived in tropical seas during the lower Carboniferous period around 350 million years ago. Each of the circular structures is the remains of a single polyp's skeleton. Corals are colonial marine organisms that live in shallow seas. They secrete an external skeleton of calcium carbonate extracted from the water. Over time, these build up into vast coral reefs, each new inhabitant building on the empty skeletons of its ancestors. This fossil was found in Scotland, indicating that the British Isles were once much closer to the Equator.
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