Spiriferida
Spiriferida is an order of extinct articulate brachiopod fossils which are known for their long hinge-line, which is often the widest part of the shell. In some genera (e.g. "Mucrospirifer") it is greatly elongated, giving them a wing-like appearance. They often have a deep fold down the center of the shell. The feature that gives the spiriferids their name ("spiral-bearers") is the internal support for the lophophore; this "brachidium", which is often preserved in fossils, is a thin ribbon of calcite that is typically coiled tightly within the shell. Spiriferids first appear in the Late Ordovician  with the appearance of "Eospirifer radiatus". They increased in diversity throughout the Silurian and underwent a dramatic evolutionary radiation during the Devonian period, reaching peak development in variety and numbers. Spiriferida survived the great Permian extinction, finally becoming extinct during the Early to Middle Jurassic. Fossils of this order are often preserved as pyrite. Taxonomy. Order Spiriferida