Crinoid Column
Genus: Crinoid (Species indeterminate from stem)
Common Name: Sea Lily, Crinoid Stem, Indian Bead
Fossil Type: Disarticulated stem segment (ossicle/columnal)
Formation: Harpersville, Late Pennsylvanian Period (Carboniferous)
Location: Coleman County, TX
Age: Information Missing
Description:
This specimen is a columnal from a Crinoid, commonly known as a Sea Lily. Crinoids are marine animals related to starfish and sea urchins, often characterized by their stalk-like bodies and feathery arms. These particular fossils are found in the Harpersville Formation.
What is a Crinoid? Crinoids, commonly known as "Sea Lilies," are not plants but marine animals belonging to the phylum Echinodermata, making them relatives of starfish, sea urchins, and sand dollars. A typical crinoid consists of a root-like "holdfast" that anchors it to the seafloor, a long, flexible stalk or stem, and a cup-like body (the calyx) topped with feathery, filter-feeding arms. While many ancient species were stalked, most living crinoids today are free-swimming (feather stars).
Anatomy & Characteristics of the Fossil
- The Stem: The fossil you have is a piece of the crinoid's stem. This stem was not a single bone but was composed of hundreds of individual, disc-like calcium carbonate plates called columnals (or ossicles).
- The Lumen: Each columnal has a central hole, called the lumen, which housed the animal's nervous system. The shape of the lumen is often a star or a circle.
- "Indian Beads": After the crinoid died, the connective tissue holding the columnals together would decay, causing the stem to fall apart. These individual, often star-shaped, discs are what fossil hunters frequently find, earning them the nickname "Indian Beads."
Crinoids were incredibly abundant during the Paleozoic Era, especially in the shallow, warm seas of the Mississippian and Pennsylvanian periods. Their population was so dense that their fossilized remains are the primary component of vast limestone formations known as "crinoidal limestone." They are excellent indicators of ancient marine environments.
