Comparative paleontology and stratigraphy of Valanginian by Jeletzky J.A., Kemper E.

By Jeletzky J.A., Kemper E.

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Additional info for Comparative paleontology and stratigraphy of Valanginian Polyptychitinae and Simbirskitinae in Sverdrup Basin (Arctic Canada) and Lower Saxony Basin (NW Germany)

Sample text

The umbilical shoulder is broadly rounded in early and intermediate whorls. However, it is gradually transformed into a more or less sharpened rim in advanced growth stages as the shells become more and more cadicone. The umbilical wall gradually becomes higher and steeper at the same time. The umbilicus is step-like rather than funnel-like. The external suture line of Euryptychites diplotomus conforms to that of other Euryptychites species in its most important features, such as the number of auxiliary lobes, but is rather variable in some details.

Latissirnus represent one morphological extreme. The other morphological extreme is exemplified by the suture of BGR, kv 370 (Figure 14b) that is characterized by very short and wide, much less deeply and elaborately denticulated lateral and auxiliary lobes. e. only slightly wider than the preceding lobes) than those of the other morphological extreme (compare Figure 14a) but the remaining saddles are similarly wide. This external suture approaches the more sturdy and less elaborately denticulated sutures of E.

5, fig. 6. 1973 Discussion. The small ammonite figured by Casey (1973, PI. 5, fig. 6) from the Paratollia-level of the Claxby Beds has an umbilicus that is wide for a Paratollia. Furthermore, its whorls are low for representatives of that genus. This specimen is ornamented exclusively by trivirgatitpartitous rib bundles consisting of high and strongly developed ribs. It could well be a predecessor of P. emslandensis (Kemper). Casey's (1973) proposal to place this specimen in Propolyptychites is contradicted by its trivirgatitpartitous ribbing habit.

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