graptolite
(grăpˈtə-lītˌ)
noun Any of numerous extinct colonial marine animals chiefly of the orders Dendroidea and Graptoloidea of the late Cambrian to the early Mississippian periods, whose fossil remains are often used to date the rocks of the Silurian and Ordovician ages.
Origin:
Origin: Greek graptos, written (from graphein, to write; see graphic)
Origin: + -lite (from the resemblance of the fossils' impressions on shale to markings on a slate)
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