Lowermost Silurian graptolites of Montagne Noire, France

Abstract

Twenty-seven graptolite species are reported from the lowermost Silurian (Rhuddanian)ascensus-acuminatusandvesiculosusbiozones of Montagne Noire in southwestern France. Four species are left in open nomenclature, four are new:Normalograptus crassus, Neodiplograptus lautus, Dimorphograptus compactusandHuttagraptus solidus.The joint occurrence ofAkidograptus ascensus, Parakidograptus acuminatusandCystograptus ancestralis, recorded in the Gabian-1 section, suggests correlation of the whole succession at this site with the middle part of a combinedascensus-acuminatusBiozone. Revision of museum collections revealed that other elements that are characteristic of theascensus-acuminatusBiozone assemblage in peri-Gondwanan Europe, such asNormalograptus trifilis, N. longifilisandNeodiplograptus lanceolatus, have been recovered from several other localities in Montagne Noire that are no longer accessible. The graptolite assemblage of the Gabian-2 section, with commonCystograptus vesiculosus, Dimorphograptus extenuatus, D. elongatusandAtavograptus atavus, belongs to the lower part of thevesiculosusBiozone, whilst the appearance ofD. swanstoniandD.?physophorain the upper part of the section represents a higher, although not the uppermost, part of the biozone. This is the first record of a diverse dimorphograptid fauna within thevesiculosusBiozone in the Gondwanan part of Europe.