| Species | Alsatites nigromontanus (GÜMBEL) |
| Author | GÜMBEL |
| Group | Alsatiten/Alpinoceraten |
| Horizon | seebachi-horizon |
| Zone | megastoma-Zone |
| Stage | Middle Hettangian |
Description
The large-growing species grows very slowly at first; the coils gain height only slowly. In medium-sized specimens this then changes and the last two or three coils become much higher, giving the ammonite a typical appearance. Similar in growth is Sunrisites hadroptychum (Wähner). The last turn of very large shells can then become less high again.
It is remarkable that the almost circular cross-section of the coils hardly changes, which makes A. nigromontanus very thick.
The distinct but not high ribs start strongly retroradiate at the suture and run in a forward open curve still leaning back over the rounded flanks to bend strongly forward near the outer side. There they join the rib of the opposite side in a strongly attenuated manner. Weak intermediate ribs, Wähner calls them "short intermediate stripes", are often present externally.
It is typical that ribs always stand irregularly and leave wider and deeper spaces in between.
Only with very large diameters does a broad low keel appear.
* Description according to Wähner (1884), supplemented
Compare
Characteristic for this species are the growth conditions in connection with the retroradiate ribbing.
Somewhat similar in growth conditions is Sunrisites hadroptychum, Wähner also describes a find here that could mediate between the two species.
Laqueoceras crebricinctum has a high oval WQ and rather flattened flanks. However, the irregular ribbing is similar.
Dimension
Dimensions at D= 200mm (according to Wähner):
Nw % v. D: ca. 52%
Wh % v. D: ca. 26%
Wb % v. D: ca. 21%
Literature
- 1884 Arietites nigromontanus Guemb. – Wähner S. 213, Taf, 24, 25
- 2000 Alsatites nigromontanus Gümbel – Kment S. 202, Taf. 3.9
