The Pristiograptus dubius (Suess, 1851) species group and iterativce evolution in the Mid- and Late Silurian
Pristiograptus dubius (Suess, 1851), one of the longest-known graptolites, is also one of the simplest and longest ranging (about 20 Ma). As well as giving rise to new genera, such as Colonograptus Přibyl (1943c) and Saetograptus Přibyl (1943c) amongst others, it also repeatedly gave rise to both broad and narrow short-lived pristiograptids, cases of iterative development. These closely resemble P. d. dubius and are often difficult to distinguish from it, especially in cases of indifferent preservation or tectonic deformation: a stratigraphy known on independent criteria is a great facilitator to identification! There is no difference in the overall range of broad versus narrow species, but the latter are more numerous. The parent species P. d. dubius survives them all and extends almost to the top of the Přídolí. The origin of the P. dubius lineages is probably through P. initialis Kirste (1919) and P. pergratus in the latest Llandovery, and P. praedubius (Bouček, 1931) in the earliest Wenlock. Pristiograptus d. dubius is a stem lineage in the sense of Urbanek (1998).