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11/03/2009 02:28:35
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P number: P520996
Caption: A fossil specimen of Polymorphites abnormis Haver. A fossil ammonite. (Mollusca, Cephalopoda, Ammonoidea.) Carsaig, 0.5 miles east-south-east of pier, Mull, Argyllshire, Scotland.
Description: This specimen of Polymorphites abnormis is an internal mould. The suture lines are clearly visible, they trace the edge of the septum or internal partitions of the shell and the shell wall. The suture lines have lobes and saddles of a fairly simple nature with some subdivided. It has an evolute, i.e. loosely coiled shell where the outer whorls enclose the inner whorls to a small extent. British Geological Survey Biostratigraphy Collection number GSE 2472. The suture is a very important feature in ammonite taxonomy as certain kinds of suture characterize distinct ammonoid families and are used for identification and classification. There are three types, goniatitic, with sharply angular zig-zag suture; ceratititic, with entire saddles but frilled lobes; and ammonititic, with finely divided and complex lobes and saddles. A general trend of complexity of suture can be seen through stratigraphic time. This specimen was found in the Lower Jurassic, Lower Lias, raricostatum zone of Carsaig, Mull.
Date taken: 01/01/2003
Photographer: Unknown
Copyright statement: NERC
Orientation: Landscape
Size: 299.60 KB; 1000 x 665 pixels; 85 x 56 mm (print at 300 DPI); 265 x 176 mm (screen at 96 DPI);
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Categories: Best of BGS Images/ Fossils  


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