Rare Grammoceras Ammonite Fossil from Upper Toarcian Jurassic Calvados France Authentic Collectable

Description

Geological Context

This Grammoceras ammonite fossil comes from the Upper Toarcian Stage of the Early Jurassic Period, approximately 183 to 174 million years ago. It was unearthed in Calvados, Normandy, France, a region renowned for its marine Jurassic deposits that yield beautifully preserved ammonites. The Toarcian seas of this area were shallow, warm, and rich in life, forming part of the Tethyan realm. Fossils from this period are particularly important for understanding evolutionary turnover during the Toarcian, a time marked by significant environmental change.

Taxonomic Classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Order: Ammonitida
• Superfamily: Hildoceratoidea
• Family: Hildoceratidae
• Genus: Grammoceras

This genus is one of the best-known Toarcian ammonites and plays a crucial role in biostratigraphy, being used as an index fossil to correlate marine layers across Europe.

Morphological Features

The Grammoceras ammonite is distinctive for its:

• Discoidal, compressed shell with very fine, dense ribbing running across the whorls.
• Involute coiling, where the inner whorls are tightly overlapped, giving a neat and symmetrical appearance.
• Smooth venter (outer shell edge), contrasting with the pronounced ribbing along the flanks.
• Well-defined growth lines and suture patterns, which can still be observed in this specimen.

These features make Grammoceras one of the most easily recognisable ammonites of the Jurassic seas, combining elegance with scientific importance.

Palaeoenvironment and Depositional Setting

During the Toarcian, the Calvados region of Normandy was submerged beneath shallow epicontinental seas. The seabed was composed mainly of fine clays and silts, which helped preserve ammonites in exceptional detail. Ammonites like Grammoceras were fast-moving, nektonic predators, using their tentacles to capture plankton and small invertebrates. Their chambered shells provided buoyancy control, allowing them to move easily through the water column.

This fossil not only represents a once-living animal but also provides a window into the ecological dynamics of Early Jurassic seas, including predator-prey interactions and the adaptation of ammonites during a time of climatic stress known as the Toarcian Oceanic Anoxic Event (T-OAE).

Scientific and Collector Importance

• Biostratigraphic Value: Grammoceras is a key index fossil for defining Upper Toarcian strata, aiding geologists in correlating rock layers across Europe.
• Evolutionary Significance: Demonstrates the adaptive radiation of ammonites following earlier Jurassic extinctions.
• Collector Appeal: Its elegant ribbing and distinctive form make it highly sought after for display.
• Educational Use: Ideal for teaching about ammonite morphology, Jurassic palaeontology, and stratigraphy.

Authenticity and Presentation

• Every fossil we sell is 100% genuine and comes with a Certificate of Authenticity.
• The photographs provided are of the exact specimen you will receive.
• A 1 cm scale cube is included in the images for accurate size reference.

This Grammoceras ammonite fossil from the Upper Toarcian of Calvados, France is a scientifically significant and visually striking specimen. Its fine ribbing, elegant coiling, and rich geological context make it a valuable addition to any fossil collection, whether for research, education, or display.