ARTHROACANTHA CARPENTERI, 2 CRINOID CROWN FOSSILS, SILICA SHALE, DEVONIAN, OHIO.

Description

ARTHROACANTHA CARPENTERI, 2 CRINOID CROWN FOSSILS, SILICA SHALE, DEVONIAN (370--400 MYA), OHIO.
Arthroacantha carpenteri is a monocyclic camerate crinoid.  This pair of specimens both have attached stems.  The larger, more mature specimen has  a well preserved calyx but only stubs of the arms are preserved; the smaller one shows the complex arms with prominant pinnules, but the top of the calyx was crushed.
Crinoids are still living, but the Paleozoic ones have the largest diversity.  Although they are called 'sea lilies', they are echinoderms
and are like sea stars (starfish)  but were attached to the sea floor upside down by a stem, with the arms up, catching plankton from the water.
Most crinoids are broken apart into tiny plates  soon after death, but these were buried alive by flows of mud that covered and preserved them.
The Middle Devonian (~380 MYA) Silica Shale was a coral reef that now has thin interlayered limestone and shale layers.  It is a
famous source of fossils because they weather out from the soft shale. It is easy to collect corals and brachiopods, but good crinoid fossils are rare.
This slab is a beautiful and valuable part of any fossil collection. It has no reconstructionor or paint but due to the softness of the
shale that encloses them it has a clear shellac(?) covering over the fossils and on the back.  It comes in a clear plastic box.
I combine shipping.
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