From the Frasnian-Famennian stratotype section at Coumiac, 1.5 km northeast of Cessenon, Montagne Noire (Fig. 3.1), approximately 100 specimens of the genera Manticoceras, Neomanticoceras, and Beloceras are available for study. Apart from some specimens collected by Böhm, the majority were assembled by Albeille and donated to the ISEM (material listed below with the prefix UMDK). All were extracted from an intense red micritic limestone that is rich in buchiolid bivalves. Conodont samples were taken from carbonate material of large body chambers. This material yielded conodonts of the conodont Zone MN12 of Klapper (1989) which points to a position immediately below the lower Kellwasser Horizon (determinations by R. Feist, Montpellier, and Z. Belka, Poznan): Ancyrodella curvata, Ancyrodella nodosa, Ancyrognathus triangularis, Icriodus symmetricus, Icriodus alternatus alternatus, Palmatolepis winchelli, Polygnathus alatus, Polygnathus sp., and Polygnathus webbi.

The investigated manticoceratid specimens (Fig. 3.3) range, in their conch diameters, from 13 to 170 mm. The largest specimen is still fully septate and indicates that the maximum diameter of the conch can be estimated to be approximately 300 mm. Almost 40 of the 90 manticoceratid specimens were sectioned with the following size ranges represented:

In many specimens, the inner whorls are well preserved and allowed the production of high-precision cross sections, meeting the largest diameter of the proto-conch. From these cross sections, acetate peels were taken and enlarged by photographic and scanning magnification (x10). On the basis of these templates, precise computer images were drawn, of which eleven are figured in Fig. 3.4.

A supplementary sample consisting of 20 specimens from the eastern margin of the Rhenish Mountains was studied. The material came from localities such as

Fig. 3.3 Manticoceras sp. from Coumiac (Montagne Noire), specimen UMDK226 (coll. Albeille), x 1.5.

Oberscheld and is stored in the Museum für Naturkunde, Berlin (MB.C. numbers). The specimens were already prepared by Jessen (a doctorate student of O. H. Schindewolf) who started a research program on the ammonoids from Büdesheim (Eifel) but never finished.

Additionally, the cross sections illustrated by Bogoslovsky (1969) and Clausen (1969) were redrawn and incorporated in the investigation. Thus, more than 70 cross sections were analyzed biometrically.

Was this article helpful?

0 0

Post a comment