Comparisons with Other Samples of Manticoceras Oberscheld

The random sample comprising 18 specimens from the eastern margin of the Rhenish Mountains displays an even wider range of conch morphologies than the sample from Coumiac. Represented are discoidal to pachyconic specimens with parallel or converging flanks (Fig. 3.10).

« specimen M275 specimen M219 specimen M218 • specimen M276

• additional specimens

« specimen M275 specimen M219 specimen M218 • specimen M276

• additional specimens

Fig. 3.9 Ontogenetic trajectories (A, C) and intraspecific variability (B, D) in Manticoceras from Coumiac. The bivariate diagrams (A, C) show the ontogenetic development of the imprint zone rate (IZR = wh--ah/wh) and flank convergence index (FCI = ww02/ww1); highlighted are the specimens UMDK 218, 219, 275, and 276. The box-and-whiskers diagrams (B, D) show the ontogenetic variations of intraspecific variability of the major conch ratios. Bold lines refer to the total range, boxes refer to the extension of the middle two quartiles, and white lines refer to the median value. Growth stages between 1 mm and 100 mm conch diameter were subdivided into 17 logarithmic intervals.

In contrast to the Coumiac sample, shapes with flattened and almost parallel-sided flanks are common. The material is stored in the Museum für Naturkunde, Berlin, under the catalogue numbers MB.C.3789 - MB.C.3806.

Of the four cross sections shown in Fig. 3.10, specimen MB.C.3791 can be attributed to Timanoceras, a genus that contains manticoceratids with crescent-shaped whorl sections. It differs from the others by its high conch width index (Fig. 3.10C). Specimens MB.C.3789 and MB.C.3790 cannot be separated in terms of morphometrics, and specimen MB.C.3792 differs by its flat conch form from the other three. However, Fig. 3.10C demonstrates that these three specimens do not represent separate ontogenetic traits; they are connected by intermediate specimens. Differences in other characters are not obvious. Accordingly, separation of distinct species within Manticoceras may be impossible on the basis of morphometrics. Because the suture lines as well as the ornament do not differ much, it appears unreasonable to retain all of the existing 40 species of Manticoceras.

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Fig. 3.10 Bivariate diagrams showing the ontogenetic development of the whorl expansion rate (WER; in A), flank convergence index(FCI; in B), conch width index (CWI = ww/dm; in C), and umbilical width index (UWI = uw/dm; in D) of sectioned specimens of Manticoceras from the eastern Rhenish Mountains. Highlighted are the four specimens MB.C.3789-MB.C.3792; cross sections x 0.75.

• specimen MB.C.3791 O specimen MB.C.3789 O specimen MB.C.3790

• additional specimens

Fig. 3.10 Bivariate diagrams showing the ontogenetic development of the whorl expansion rate (WER; in A), flank convergence index(FCI; in B), conch width index (CWI = ww/dm; in C), and umbilical width index (UWI = uw/dm; in D) of sectioned specimens of Manticoceras from the eastern Rhenish Mountains. Highlighted are the four specimens MB.C.3789-MB.C.3792; cross sections x 0.75.

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