Abstract

Calceocrinids (Crinoidea, Inadunata) adopted a recumbent, 'runner' mode of life, with concommitant structural adaptions becoming increasingly refined through evolution. Six new species are described from the Ordovician and Silurian of Oklahoma, Illinois, Tennessee, Iowa, and Ontario, and the Mississippian of Indiana and Kentucky: Calceocrinus constrictus, C. multibifurcatus, Grypocrinus multibrachiatus, Halysiocrinus septarmatus, H. springeri, and Calceocrinus pustulosus Johnson, previously unpublished. Grypocrinus is thought to be polyphyletic; Halysiocrinus is descended from Deltacrinus or its ancestor. Presence of Calceocrinus in the Black River Stage of Oklahoma reopens the question as to whether Anulocrinus or Cremacrinus is the ancestral stock of the Calceocrinidae.

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