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Ammonites are an extinct order of carnivorous mollusks that were closely related to the squid, octopus, cuttlefish, and the chambered nautilus. Ammonites mysteriously became extinct at the same time as the dinosaurs some 65 million years ago. The term "ammonite" means "Ammon's Stone." The name was given to these coiled fossils by the Egyptians who noted their resemblance to the horns of their ram headed god, Ammon. Ammonites flourished in oceans for approximately 330 million years.
Ammonites are easily recognized by their beautiful geometrically coiled shells. These shells were secreted by the animal and continued to grow and provide protection for the creature throughout its life. The animal itself probably very closely resembled a modern day squid living in the end of the shell (similar to the chambered nautilus). An ammonite could control its buoyancy much like a submarine, filling its chambers in the shell with either gas or fluid. Ammonites became so prolific that they filled nearly every niche in the ocean.
This specimen is also offered in the fluorescent section under South Dakota fluorescent minerals and fossils. Also check out other South Dakota fluorescent offerings under the Fluorescents section. Then click on the "To view specimen material from South Dakota" link. Some other normal light photos will be shown there as well.
The specimen is either Didymoceras nebraskense or Didymoceras stevensoni. Both are found in the same area. Didymoceras is easily identified by its loosely twisting coils. The circular whorl sections have two rows of paired tubercles (bumps) along the outside edge. The ribs are irregularly bifurcated (divided in two). The coils can be clockwise or counter-clockwise. They lived during the Upper Campanian Stage of the Upper Cretaceous (76-75MYA). Because of its loosely coiled shape (like an open cork screw), whole specimens are rarely found. Specimens such as the one below are typically all that are found.
Didymoceras
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Quantity in Basket:
None
Code: SDA-105N
Price: $30.00
Shipping Weight: 0.36 pounds
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Time: Upper Cretaceous, Upper Campanian, approximately 76-75
million years ago.
Location: Pierre Shale, South Dakota, USA
Dimensions: 3-1/8" x 1-3/8" x 1-1/4"
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