Crinoid Pieces

$26.50

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Description

This lot consists of 7 pieces of crinoid stems, each of varying length from 1 inches to 1 1/2 inches.  

Crinoids are an ancient fossil group that first appeared in the seas of the Middle Cambrian, about 300 million years before dinosaurs. They flourished in the Palaeozoic and Mesozoic, and some survive to the present day. Although sometimes different in appearance from their fossil ancestors, living forms provide clues about how fossil crinoids must have lived.

Crinoids are marine animals belonging to the Phylum Echinodermata and the Class Crinoidea. An array of branching arms (brachials) is arranged around the top of a globe-shaped, cup-like structure (calyx) containing the main body of the animal. In many fossil forms the calyx was attached to a flexible stem that was anchored to the sea bed.

The skeleton is made of the mineral calcite, and consists of hundreds of individual plates of different shapes and sizes. Decay of the soft tissue that held many of these plates together means that complete specimens are rare, but parts of the stem are common fossils.

he stem typically consisted of disc-like plates (columnals) stacked on top of each other. Individual columnals were rounded, elliptical, square, pentagonal or stellate, and some plates were decorated with petal-like designs. The different shapes of crinoid stem plates are useful for classification, but some fossil crinoids, like many modern forms, lack stems.

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