Ordovician Graptolites Assemblage

Phyllograptus archaios

Phylum Hemichordata; Class Graptolithina

Geologic Time: Lower Ordovician

Size: Graptolites are 17 to 30 mm

Fossil Site: Fillmore Formation, Millard County, Utah

Phyllograptus GraptolitesThis is a fine assemblage of graptolites known as Phyllograptus archaios. 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. This genus draws its name from its leaf-like shape. There are a dozen example sof this large species, along with a few thoracic segments of a trilobite at the top.

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