Echinoderms includes the marine group of animals of Echinoids, Crinoids, Sand Dollars, and Starfish. The earliest Echinoid (Sea Urchins or Urchin) fossils date to the Ordovician, 450mya, and they have been so successful that they have survived to the present. Echinoid fossils are more commonly found in the Cretaceous period, especially in the British Chalk.
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