Uintacrinus socialis Rare Crinoid Colony from Kansas Chalk

Uintacrinus socialis

(Colony of stemless crinoids)

Phylum Echinodermata

Geological Time : Cretaceous

Size: Matrix measures 38 by 26 inches

Fossil Site: Niobrara Formation Smoky Hill Chalk, Gove County, Kansas

This echinoderm fossil slab contains 12+ crinoid calyxes, some with long arms. The colony exhibits superb detail on matrix that measures 38" x 26". Traditionally, calyxes are uniform in size and preserved in lateral view; however, this slab contains several different-sized calyxes that are preserved in both lateral and ventral view. A natural iron oxide stain gives the specimen a rich, reddish-brown color. Uintacrinus, a stemless crinoid that lived in free-floating colonies (composed of many individuals), is among the rarest invertebrate fossils, and possibly one of the rarest of all described species from the Niobrara chalk formation. Only one zone (normally 2 to 3 inches thick) out of over 800 feet of chalk sediment, produces these crinoids. This is a wonderful and historically significant Kansas chalk fossil.

  • Cobban, WA Occurrences of the Free-Swimming Upper Cretaceous Crinoids Uintacrinus and Marsupites in the Western Interior of the United States. United States Geological Survey Bulletin 2113 1995.
  • Grinnell, GB On a new crinoid from the Cretaceous formation of the west. American Journal of Science 12(3):81-83 1876.

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