These ammonites are representatives of the genus Dayiceras, which were discovered some time ago in Portugal. The shell preservation is excellent and offers a variety of details that have to be carefully worked out of the very hard rock. In order not to damage them, the preparation must be done particularly careful and gentle. 

The preparation is therefore relatively time-consuming. Excessive stress causes the rock to break in a glass-like and uncontrolled manner. Likewise, the shell also breaks when too much pressure is applied. However, the rock is very tough and hard. The preparation is mainly done using fine air abrasives so as not to damage the high and closely spaced ribs. The fine central row of thorns on the keel of the ammonites stands out as another special feature of this genus.  

Fossil: Dayiceras sp.

Locality: Portugal

Formation: Lower Jurassic, Pliensbachian

Diameter of the biggest ammonite: 10 cm (3.9 inches)

Work required: 22 hours