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Excerpts from Jim Conrad's
Naturalist Newsletter
from the July 21, 2008 Newsletter, after a visit to Land Between the Lakes National Recreation Area in northwestern Tennessee:
CRINOID STEMS
Gravel along most of Land Between the Lakes' shores often contained crinoid stems and segments of stems. Rock strata at LBL are Cretaceous in age, so crinoids eroded from those strata are ±145.5 to ±65.5 million years old. You can see a crinoid-rich rock from there above.
As a kid I called fossilized crinoid segments "Indian beads," and I strung many bracelets of them, for gravel around our family home also was rich in them.
Crinoid stems found loose and in rocks are fossils of sea animals known as sea lilies or feather stars. The segmented stems are like stacked Life Savers, atop which arises something like an upside-down, frilly-armed starfish. In fact, crinoids are members of the phylum Echinodermata, which also includes starfish, sea urchins and sand dollars.
Crinoids have inhabited Earth's waters since at least the Ordovician, some 500 million years ago. However, they're still with us as "living fossils," the stalked kind mostly living in waters deeper than 600 feet.