Cosmoceras sp. Ammonites
Phylum Mollusca, Class Cephalopoda, Subclass Ammonoidea, Order Ammonitida
Geological Time: Jurassic Callovian Stage
Size (25.4 mm = 1 inch): 71 mm diameter on a 140 mm by 125 mm base
Fossil Site: Ulyanovsk, Russia
Fossil Code: RA368
Price: Sold
 Description:
A superb large example of an ammonite of the genus Cosmoceras of the
Callovian Stage (161 m.y.a) deposits of Russia. This fine example
has had one side of the shell removed to allow you to see the intricate
detail of the interior. You can easily see the individual chambers
which were successively occupied in a spiral pattern by the ammonite
as it grew. The septa (divisions) between the chambers are evident
as the fine line between them. The environment was anoxic, leading
to formation of Iron Pyrite (Fool’s Gold), crystals of which
line each chamber for a dramatic effect. There is a second, smaller
(23 mm) example which has been attached in the center to allow you
to see what the ammonite’s original appearance had been. It
displays well upon this dark concretionary matrix with the fine sand
layer affording a good contrast. |
