SilesianTriassic

Germanonautilus cf. dolomiticus

Middle Triassic, Gogolin Beds, Upper Silesia, Poland

The specimen is a fragment of the outer whorl of a Middle Triassic nautiloid preserved in the form of a steinkern.

The preserved fragment measures 21 cm length measured along the outer curvature. Its width at its widest point is 11.5 cm, and at its narrowest point 9 cm.

In cross-section, the whorl is trapezoidal, with flat lateral and ventral surfaces.

In ventral view, the preserved fragment resembles a blunt wedge. Five sutures are visible at the narrower end, the sixth being the edge along which the fragment broke off. The sutures are simple and weakly sinuous, consistent with nautiloid cephalopods. The last two sutures in the central part of the specimen are clearly condensed compared to the previous ones; from this point on, no sutures are visible (right part of the specimen on the photo 1).

The dimensions of the preserved fragment suggest that the individual was large. The increased density and subsequent lack of sutures may suggest that the specimen represents an anterior fragment of a phragmocone and part of the body chamber, and that it was a near-adult or adult individual.

The state of preservation does not allow for a certain species identification, but considering that the specimen is from the Lower Muschelkalk (Gogolin Beds), it strongly suggests that specimen may represent Germanonautilus cf. dolomiticus.

A large, subcircular feature is visible on the ventral surface of the specimen. It does not appear to be the result of weathering or recent mechanical damage. The surface is coherent, and no fracture is visible. At present, I am unable to determine its origin.

References

• Niedźwiedzki, R., Surmik, D., Chećko, A., Paszcza, K., Jain, S., & Salamon, M. A. (2021). The oldest nautiloid recorded from the Triassic Germanic Basin and the first ammonoid from the Aegean (Middle Triassic) of Poland. Annales de Paléontologie, 107(3), 102507. https://doi.org/10.1016/j.annpal.2021.102507