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Pyritized steinkern under preserved calcitic shell. Index fossil for the gibbosus subzone. Literature: Quenstedt, F.A. (1883-85): Die Ammoniten des Schwäbischen Jura. Bd.1 Der Schwarze Jura (Lias). Schweizerbart'sche Verlag.

Pyritized steinkern with shell remnants. This species is the index fossil for the margaritatus zone. Literature: Quenstedt, F.A. (1883-85): Die Ammoniten des Schwäbischen Jura. Bd.1 Der Schwarze Jura (Lias). Schweizerbart'sche Verlag.

Remnants of the original aragonite shell were still on this fossil when found, but they were removed in order to expose the pyritized steinkern mold. The overwhelming majority of the fossils at Buttenheim show this type of preservation, although pure or partial calcite molds also occur. This is also the index fossil for the solare subzone, which is only recognized in Germany. For information on identification of this species see Pleuroceras spinatum under Collections. Old German Chronostratigraphy: Lias (Schwarzjura) delta Literature: Simonsen,S. et al (2012): Die Tongrube Buttenheim, 2. überarbeitete Auflage, Verlag Der Steinkern

The first three photos show an extremely well-preserved specimen of this species which was gifted to me by an aquaintance. The last three show an accumulation of strongly pyritized ones from the clay pit at Buttenheim in Bavaria, the largest of which has a diameter of 5cm. This is the index fossil for the spinatum zone and also for the spinatum subzone, an informal designation in Germany. The clay pit at Buttenheim is world-reknowned for its upper Pliensbachian ammonite fauna. It is one of, when not the best site worldwide for studying the breadth of variation and development of form through time, particularly of the various species of the genus Pleuroceras. Zones, subzones and horizons are all easily accessible and layed out like the pages of a book here. This species looks quite similar to P. solare, but is relatively easily distinguishable upon closer study. The extremely strong ribs rise to a point slightly above the keel, whereas the somewhat weaker ones of P.solare lie a little below its keel. The whorls of P.spinatum are also somewhat wider than those of P.solare. Old German Chronostratigraphy: Lias (Schwarzjura) delta Literature: Simonsen,S. et al (2012): Die Tongrube Buttenheim, 2. überarbeitete Auflage, Verlag Der Steinkern