Abstract

The development and distribution of thin-walled pelagic tentaculites (Dacryoconarida) and graptolites in the Devonian period are considered. Graptolites, and tentaculites were inhabitants of the open seas (plankton, nekton) and quickly adapted themselves to changes of environment.

Well established successions of tentaculite faunas in Central Europe make it possible to correlate successfully many tentaculite-bearing series in Africa, Asia, Australia, and North America. In many cases, the individual series might be thus classified in quite a different way than it has so far been considered feasible. Not only tentaculites are involved but also the stratigraphical alignment of some species of graptolites has been revised, which up till now have been ascribed to much lower beds.

The evolution of the graptolites suddenly changes at the boundary between the Silurian and the Devonian. Typical representatives of the genera Pristiograptus and Colonograptus become extinct and the development of a quite new trend of monograptids commences (Monograptus angustidens, M. uniformis, M. aequabilis, etc.). The tentaculites appear somewhat higher up above this boundary line.

Development of the tentaculites can be followed up to the Frasnian and that of the graptolites up till the end of the Pragian, i.e. till the end of the Lower Emsian. In view of the fact that in the last known zone (Monograptus atopus) several species are still represented in association, it cannot be excluded that future investigations will disclose the occurrence of the graptolites in still younger Devonian beds.