| Species | Storthoceras frigga (WÄHNER) |
| Author | WÄHNER |
| Group | Psiloceraten |
| Horizon | curviornatum-horizon |
| Zone | megastoma-Zone |
| Stage | Middle Hettangian |
Description
After a distinct nodule stage, the weakly S-shaped ribs begin, bending strongly forward near the external side and crossing it in young specimens. Later the external side is smooth, because the ribs go out before. If the shell is well preserved, however, one can see that growth strips cross the external side instead of the ribs. The cross-section of the coils is highly oval, the flanks flattened; the external side often even appears sharpened because of the small width of the coils. The species is very common in small sizes up to about 50mm in diameter. Large specimens have not yet been documented with certainty.
* Description according to Wähner (1886), supplemented
Compare
This species has proven to be a real "lead fossil" of the Middle Hettangian. The small-sized shells are easy to recognise and very common. Even in outcrops where
only single ammonites of this time period can be found, Storthoceras frigga is always present. The species is very easy to identify by the highly oval coils and the low, straight and externally strongly protruding ribs that cross the externa.
Dimension
Dimensions at D= 35mm (according to Lange):
Nw % v. D: ca. 37%
Wh % v. D: ca. 37%
Wb % v. D: ca. 23%
Literature
- 1886 Aegoceras frigga n.f. – Wähner S. 106, Taf, 23.1-3
- 1952 Storthoceras frigga Wähner– Lange, S. 127
