MONOGRAPTUS-DEUBELI AND PRAEDEUBELI (WENLOCK, SILURIAN) IN THE ASIAN PART OF THE FORMER SOVIET-UNION

During the last decade the sequence and composition of the later Homer ian (Wenlock) graptolite fauna has become comparatively well known in many regions of the world. A complete and detailed graptolite biozonat ion has been elaborated in Europe, and partly confirmed in Australia a nd Arctic Canada. Valuable new data have been obtained from several wi dely scattered areas within the Asian part of the former U S. S. R. M. praedeubeli Jaeger (rare) and M. deubeli (common) have been found in the Homerian sequences in the Novosibirsk Islands and Novaya Zernlya. as well as in the southern Urals and the Turkestan-Alai Mountains of c entral Asia. In sections studied here, especially in the Alai Range, b oth species have well defined stratigraphic ranges in a variety of pel agic and hemipelagic facies. Their well established taxonomy based on sicular shape and thecal structure allows their recognition in materia l of different preservation. They belong to a single phylogenetic line and can be used as important biostratigraphic markers for interregion al correlation, especially considering the distinct differences in the composition of associated monograptids. Thus, members of the Pristiog raptus idoneus - Lobograptus? claudiae lineage parallelling the develo pment of M. pmedeubeli and M. deubeli in the Homerian of central Asia, Australia, Arctic Canada and Arctic Russia, are unknown from European and northern African sections.