Spiriferida

Spiriferida is an order of extinct articulate brachiopod, fossils of 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 support, which is often preserved in fossils, is a thin strip of calcareous material that is typically coiled tightly within the shell.

Fossil spiriferids first appear in the Ordovician period. They were rare during the Silurian, but underwent a dramatic evolutionary radiation during the Devonian period, reaching a peak development in variety and numbers at that time. After surviving the great Permian extinction, the order finally went extinct during the Jurassic period.

Fossils of this order are frequently preserved as pyrite (fools gold).