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updated July 7, 2005
| On the anisograptid affiliation of 'Dictyonema' flabelliforme (Eichwald 1840) and its nomenclatural consequences Bernd-Dietrich Erdtmann Geological Society Special Publication No 20, pp. 21-25 |
The recent discovery of Radiograptus stratigraphically below a series of morphological predecessors
to the planktic siculae 'Dictyonema' flabellforme-sociale groups suggests a phyletic derivation of
these forms from the anisograptid Radiograptus (Bulman 1950) and thus requires a taxonomic
revision of the planktic species of Dictyonema, D. retiforme (Hall 1843, is a Silurian benthic
member of the family Dendrograptidae. The genus Dictyonema must be restricted to represent the
approximately 140 sessile species of cone-shaped, dissepimentous, dendroid graptolites (upper
Cambrian - Carboniferous), whereas the homeomorphic planktic forms, now belonging to the family
Anisograptidae, require a new generic name. The names Rhabdinopora (Eichwald 1855),
Graptopora (Salter 1858) and Dictyograptus (Hopkinson &Lapworth 1875) are valid nomina oblita
for this group of graptolites, with Rhabdinopora having priority. Dictyograptus would be a much
favoured alternative name because of its long historical application to the 'flabelliforme-sociale grop"
and its euphonic semblance to Dictyonema, but being a junior name, its preference over
Rhabdinopora would require suppression of the rule of Priority and is not recommended. The
history of the generic status of Rhabdinopora flabelliformis (Eichwald 1840) and of R. socialis
(Salter 1858) is briefly reviewed.
to the planktic siculae 'Dictyonema' flabellforme-sociale groups suggests a phyletic derivation of
these forms from the anisograptid Radiograptus (Bulman 1950) and thus requires a taxonomic
revision of the planktic species of Dictyonema, D. retiforme (Hall 1843, is a Silurian benthic
member of the family Dendrograptidae. The genus Dictyonema must be restricted to represent the
approximately 140 sessile species of cone-shaped, dissepimentous, dendroid graptolites (upper
Cambrian - Carboniferous), whereas the homeomorphic planktic forms, now belonging to the family
Anisograptidae, require a new generic name. The names Rhabdinopora (Eichwald 1855),
Graptopora (Salter 1858) and Dictyograptus (Hopkinson &Lapworth 1875) are valid nomina oblita
for this group of graptolites, with Rhabdinopora having priority. Dictyograptus would be a much
favoured alternative name because of its long historical application to the 'flabelliforme-sociale grop"
and its euphonic semblance to Dictyonema, but being a junior name, its preference over
Rhabdinopora would require suppression of the rule of Priority and is not recommended. The
history of the generic status of Rhabdinopora flabelliformis (Eichwald 1840) and of R. socialis
(Salter 1858) is briefly reviewed.