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The fossil record of the clypeasteroids is extremely good and they are found at all latitudes and in all continents. Clypeasteroids arose from amongst the paraphyletic cassiduloids in the late Cretaceous or early Tertiary and rapidly diversified during the Eocene. During this period they came to replace cassiduloids as the dominant echinoid group in inshore clastic facies. Today they are probably more diverse than at any time in the past. |