Article: New Late Silurian monograptids from Kazakhstan
Tatyana N. Koren
Some new and previously unrecorded graptolites are described from sections through the Tokrau horizon in the north-east Balkhash area of Kazakhstan, USSR. They include Monograptus anerosus sp. nov., M. balaensis sp. nov., M. beatus sp. nov., M. microdon aksajensis subsp. nov., M. mironovi sp. nov., M. nimius sp. nov., M. prognatus sp. nov., M. supinus sp. nov., M. willowensis (Berry and Murphy), and Neocucullograptus kozlowskii Urbanek. These species were collected through approximately 750 m of section referable to the lochkovensis, bouceki, and perneri zones. A local zone of M. microdon aksajensis is established for the first time in the uppermost Silurian of Kazakhstan. The successive zonal associations contain almost all species known in the Pridoli beds of the Barrandian area. The new graptolite fauna includes monograptids having uniform or biform thecae with apertural additions of differing structures. Most of the apertural apparatuses are unusual for the Pridolian stage of graptolite evolution, although they are not new but are partly homeomorphs of those known in the Ludlow Series. The variety of thecal structures discovered in the Kazakhstan collections suggests that the Pridolian monograptid faunas are less monotonous than previously suggested.