REFINED TAXONOMY OF ROBUST NONPLATFORMED CONODONTS IMPROVES CORRELATION OF THE KAZANIAN TO THE WEST TEXAS STANDARD

The taxonomy of very similar robust nonplatformed apparatuses ascribed to Sweetina and Stepanovites can be differentiated by the Pa element. Material described by Wardlaw and Collinson (1986) in establishing the genus Sweetina based on its nonplatformed pastinate Pa element illustrated two morphotypes. One, from Nevada, that has a short lateral process and a large cusp, largest of all denticles (including the holotype). The other, from Utah, has a short lateral process but the last denticle on the anterior process, directly before the cusp, is the largest denticle, larger than the cusp. This later form is widespread in the Kazanian deposits of the Mid-Volga region. It has been named recently Kamagnathus (Chernikh, Khalymbadzha, and Silantiev, 2001). The Kamagnathus Pa element is similar to that of Stepanovites. New material from the Upper Kazanian (Prikasan beds) show that Stepanovites is similar to Kamagnathus in that its last anterior denticle just before the cusp is larger than the cusp (hypertrophied), but it completely lacks a lateral process. Therefore, all three genera are valid, with Kamagnathus common to both the Volga region and the western USA and Stepanovites only in the Volga region and Sweetina only in the western USA in this comparison. The stratigraphic range of Kamagnathus in the territory of the European part of Russia is Kazanian. In the USA, the forms close to the Lower Kazanian species Kamagnathus khalimbadzhae occur in the Roadian (zone Neogondolella serrata - Neostreptognathodus newelli - Penniculauris bassi of Wardlaw, Collinson, 1986). The upper Kazanian substage is most probably also Roadian, because Merrillina galeata, which is characteristic of higher stratigraphic horizons (Wordian) is absent in the Upper Kazanian of the Mid-Volga Region. Because the lower Kazanian correlates with the lower Roadian and I suggest the upper Kungurian correlates with the Cathedralian, it appears the Ufimian may lose its status as a stage. Its stratigraphic range and position are uncertain: is the Ufimian a part of the Kungurian or a part of the Kazanian?