DIRK WIERSMA / SCIENCE PHOTO LIBRARY DIRK WIERSMA / SCIENCE PHOTO LIBRARY
Fossil crinoid stalks. Rock containing crinoid, or sea lily, fossils. This fossil dates from the Silurian period (between 443 and 416 million years ago). Crinoids are marine echinoderms that have been in existence for 500 million years. Thousands of extinct crinoid species have been found as fossils, but only a few hundred species still exist today. They attach themselves to the sea floor with their stem and use their feathery arms to filter food from the water. This fossil was found in Morocco and measures 35 centimetres wide.
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