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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