Artistic Pyritized Pleuroceras Ammonite and Brachiopod Association

Pleuroceras spinatum with Brachiopoda

Phylum Mollusca, Class Cephalopoda, Subclass Ammonoidea, Order Ammonitida, Family Pleuroceratidae

Geological Time: Jurassic Lower Lias

Size (25.4 mm = 1 inch): Ammonite: 65 mm diameter Brachiopod; 20 mm across

Fossil Site: Untersteurmig, Germany

Ammonite and Brachiopod AssociationThis is an excellent example of ammonite beauty in Pleuroceras spinatum of the Lower Lias (200 m.y.a) deposits of Germany. It more resembles a bronze sculpture than the remnants of a living organism. It is found with an attached Brachiopod, a shelled animal which looks like the more familiar bivalves of today: the clams. The easiest way to distinguish Brachiopods from Bivalves is in the symmetry of the shells. The plane of symmetry in a Brachiopod shell passes through the individual shell, while the Bivalvia have a plane of symmetry that passes between the individual shells themselves. The environment in which these were preserved was anoxic, leading to formation of Iron Pyrite (Fool’s Gold). These are essentially solid pyrite, with only the intricate suturing pattern that gave strength to the shell for minimum weight highlighted in a delicate white tracery. The ridge along the dorsal edge is the remnant of the siphuncule, the means by which the ammonite “shifted ballast” in order to rise and fall in the water column. This most artistic specimen made all the more interesting by virtue of the association with the Brachiopod.

See more: Ammonite Fossils

click ammonite pictures to enlarge

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