The Ordovician and Silurian benthic graptolite Ptilograptus Hall, 1865 (Graptolithina, Dendroidea)

Abstract

The genus Ptilograptus is re-described from its type species and a revision of the included taxa is attempted. The genus is widely distributed from the Darriwilian (Middle Ordovician) to the Ludlow (Ludfordian) or even the Přídolí (upper Silurian), but its origin is uncertain and may be much earlier. The characteristic zigzag shaped first order stipes and alternating lateral second order stipes formed through monoprogressive branching are characteristic and are not shared with other dendroid genera. Ptilograptus is transferred from the Callograptidae to the Dendrograptidae based on its stipe and thecal development. Notes on the validity of all 41 described Ptilograptus species are provided, of which 18 species are accepted as valid and useful.