Great Ordovician Radiation Graptolite Fossils

Description: This is a fine example of a graptolite known as Didymogratus denticulatus. The species derives its name from the toothlike serrations. Graptolites are colonial animals belonging to the hemichordates. The term originates from the patronymic genus Graptolithus. The graptolites have a cosmopolitan distribution, and so serve as index fossils in many locations. The Graptoloidea were pelagic, drifting with the currents, and were the most important members of the plankton before dying out in the early Devonian.