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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.
[Greek graptos, written (from graphein, to write; see graphic) + -lite (from the resemblance of the fossils' impressions on shale to markings on a slate).]
(Palaeontology) any extinct Palaeozoic colonial animal of the class Graptolithina, usually regarded as related to either the hemichordates or the coelenterates: a common fossil, used to determine the age of sedimentary rocks
[C19: from Greek graptos written, from graphein to write + -lite]
any extinct marine animal of the class Graptolithina that grew in branching, floating colonies preserved as traces in Ordovician through Mississippian deposits.
[1830–40; < Greek graptó(s) painted, marked with letters (v. adj. of gráphein to write) + -lite]
grap`to•lit′ic (-ˈlɪt ɪk) adj.