A reorganization and proposed phylogenetic classification of planktic Tremadoc (early Ordovician) dendroid graptolites

The type species of Dictyonema is D. retiforme Hall, 1851 from the Middle Silurian Rochester Shale of New York. Although incomplete, the type specimen probably belongs to the benthic group of dendroid graptolites which ranged from the Late Cambrian to early Late Carboniferous. It is proposed that the plank tie, near-cosmopolitan 'Dictyonema' flabelliforme is phylogenetically quite distinct and belongs to the unattached coni-siculate dendroid family Anisograptidae Bulman, with Radiograptus Bulman as probable ancestor. The Anisograptidae are not directly related to the benthic dendroid family Dendwgraptidae Roemer, of which Dictyonema is a member, although they may be indirectly descended from it. The planktic species 'Dictyonema' flabelliforme is revised and referred to the genus Rhabdinopora Eichwald, 1855. 'Dictyonema' norvegicum Kjerulf and 'D' graptolithinum Kjerulf are regarded as junior
synonyms of Rhabdinopora flabelliformis (Eichwald).
The coni-siculate planktic family Anisograptidae is reorganized into three subfamilies. The Anisograptinae n. subfam. includes essentially horizontal pauci- or non-dissepimentous genera (Radiograptus, Staurograptus, Anisograptus, Adelograptus, Aletograptus, Triograptus and Kiaerograptus); the Rhabdinoporinae n. subfam. includes pendent conical genera (Rhabdinopora, Bryograptus and doubtfully Sagenograptus); and the (possibly polyphyletic) Clonograptinae n. subfam. includes horizontal forms principally developing from a single dicalycal bud of th11 (Cionograptus, Temnograptus, ?Stellatograptus).