Silurian Graptolite Fossil from Rochester Shale

Description: This is a fine example of a Silurian fenestrate dendroid graptolite known as Desmograptus micronematodes. Graptolites are colonial animals belonging to the hemichordates. The term originates from the patronymic genus Graptolithus. The graptolites were pelagic, drifting with the currents, and were the most important members of the plankton before dying out in the early Devonian. The window-like structures (fenestrae) were also seen in Bryozoans as a result of convergent evolution to serve as filters.