is edited and periodically updated by
Piotr Mierzejewski, the Count of Calmont and Countess Maja A. Korwin-Kossakowska
since 2002
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.