Fossil Crinoids (Uintacrinus socialis), Smithsonian National Museum of Natural History, Washington, D.C.
Because many crinoids resemble flowers, with their cluster of waving arms atop a long stem, they are sometimes called sea lilies. But crinoids are not plants. Like their relatives—starfishes, sea urchins, sea cucumbers, and brittle stars—crinoids are echinoderms, animals with rough, spiny surfaces and a special kind of radial symmetry based on five or multiples of five.
Crinoids have lived in the world’s oceans since at least the beginning of the Ordovician Period, roughly 490 million years ago. They may be even older. Some paleontologists think that a fossil called Echmatocrinus, from the famous Burgess Shale fossil site in British Columbia, may be the earliest crinoid. The Burgess Shale fossils date to the Middle Cambrian, well over 500 million years ago. Either way, crinoids have had a long and successful history on earth…
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