Eubostrychoceras japonicum

The unprepared geode, width approx. 14 cm

The unprepared geode,
width approx. 14 cm

The worn living chamber is
exposed piece by piece

The worn living chamber is
exposed piece by piece

Intermediate stage of the preparation on the
anterior end of the Geode

Intermediate stage of the
preparation on the anterior end
of the Geode

Little by little the whorls are worked out

Little by little the whorls
are worked out

The final result after 20 hours
of preparation

The final result after 20 hours of preparation

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Here is a very fine example of the heteromorph ammonite Eubostrychoceras, very typical for the Japanese Upper Cretaceous. These ammonites are found in geodes that are usually quite hard and not easy to prepare. This specimen was in a relatively soft stone, which allowed the preparation with fine air abrasives, improving the result significantly.

Another difficulty next to the hardness of the stone is the bizarre morphology of this species. The uncoiled whorls and beaded ribs make it quite easy to damage the fossil while removing matrix. That’s why it is necessary to slowly approach the ammonite shell in order to keep it fully intact. To showcase all the beauty of this ammonite, the whorls were prepared from the inside too. This way the ammonite appears to be “floating” on the geode.

Fossil: Eubostrychoceras japonicum

Locality: Haboro-Region, Hokkaido (Japan)

Formation: Upper Cretaceous, Turonian

Length of the ammonite: 8 cm

Work required: 20 hours

The specimen and its preparation were published on the Steinkern website in 2020:

FREITAG, P. (2020): Ammonites of Hokkaido: Preparation of an Eubostrychoceras japonicum
Link to the article: https://www.steinkern.de/english-articles/1347-eubostrychoceras-japonicum-ev.html