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Showing results for tags 'fuegerolles'.
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This species was one of the most common of its time, but nevertheless it is used as the index fossil for the subzone since its occurence is practically limited to it. It is not easy to differentiate it from the species D.athleticum, which occurs in the same subzone. One main difference is that D.commune has a more rounded whorl section than D.athleticum, which is more oval. Another is that the number of ribs per whorl by D.athleticum remains constant, whereas D.commune has less ribs on the outer whorls as on the inner ones. The first specimen is from France (4 photos), the next 2 photos show a pyritized version in a concretion from a site near Whitby, Yorks., UK as well as the cut and polished version in the last photo. Both come from the Whitby Mudstone Formation. It's always interesting to observe how the same species can be preserved so differently depending in the particular conditions under which they were fossilized. Literature: Howarth, M.K. (1973): The Stratigraphy and Ammonite Fauna of the Upper Liassic Grey Shales of the Yorkshire Coast. Bulletin of the British Museum (Natural History) Geology. Vol.24 No.4