A critical graptolite correlation into the Lower Ordovician of Gondwana

The early Ordovician was a time of maximum faunal provinciality. Correlation between strata deposited at low palaeolatitudes and those deposited close to the Ordovician pole in Gondwana is accordingly particularly difficult. The graptolite used to define the base of the internationally accepted Floian Stage, Tetragraptus approximatus, is essentially a lower latitude species. The discovery of a closely related and coeval species, T. akzharensis, in the early Ordovician of the Montagne Noire is reported. It occurs at the same level as the acme of the trilobite Taihungshania miqueli. The new record permits a direct tie with the earliest part of the Floian Stage and the shelly faunas typical of much of western Gondwana.