Description
Rare Kosmoceras (Spinikosmoceras) transitionis Ammonite from France
This is a rare Kosmoceras (Spinikosmoceras) transitionis ammonite fossil from the Callovian stage of the Middle Jurassic, discovered near Villiers-sur-Mer, France. Dating back approximately 166 – 163 million years, this fossil represents an exceptional example of the Kosmoceratidae lineage, a group of ammonites well known for their ornate ribbing and spines. The specimen you see photographed is the exact fossil you will receive, shown with a 1 cm scale cube for accurate sizing.
Each of our fossils is 100% genuine, carefully prepared, and supplied with a Certificate of Authenticity. This ammonite is not only a stunning natural relic but also an important reference fossil for collectors and researchers of Jurassic marine life.
Geological Background – Callovian Stage
The Callovian stage marks the late Middle Jurassic, between 166 and 163 million years ago. During this time, Europe and northern France were submerged beneath warm, shallow seas that supported an abundance of marine life. The region around Villiers-sur-Mer is particularly well known for producing exceptionally preserved ammonites, bivalves, and marine reptiles, making it one of the classic fossil localities of Normandy.
Kosmoceras and its close relatives were widely distributed ammonites, and many species serve as valuable index fossils for the Callovian stage. Their distinct morphology allows geologists to pinpoint precise layers of Jurassic rock, making them crucial tools in paleontological and geological research.
Scientific Classification
- Genus: Kosmoceras
- Subgenus: Spinikosmoceras
- Species: Kosmoceras (Spinikosmoceras) transitionis
- Order: Ammonitida
- Superfamily: Stephanocerataceae
- Family: Kosmoceratidae
- Geological Stage: Callovian, Middle Jurassic (c. 166 – 163 million years ago)
- Locality: Villiers-sur-Mer, Normandy, France
Distinctive Morphological Features
The Spinikosmoceras transitionis ammonite displays the classic features for which this group is renowned:
- Intricate ribbing running across the shell, adding both structural strength and visual beauty.
- Spine-like tubercles along the flanks, characteristic of the Spinikosmoceras subgenus.
- A moderately involute coiling pattern, where inner whorls are partly covered by later growth.
- Shells that could vary in size but consistently displayed ornate ornamentation, making them easily distinguishable from other ammonite groups.
These features made the species an important element in Callovian biostratigraphy and also a striking addition to any fossil collection.
Paleoecology and Depositional Setting
Ammonites such as Kosmoceras (Spinikosmoceras) transitionis were nektonic predators, moving freely through the Jurassic seas and preying on small molluscs and crustaceans. Their chambered shells acted as buoyancy devices, allowing them to navigate different water depths with ease.
The Callovian seas around Villiers-sur-Mer were part of a rich shallow marine ecosystem, dominated by cephalopods, bivalves, belemnites, and marine reptiles. The fine-grained sedimentary deposits in the region enabled exceptional fossil preservation, capturing even delicate ornamentation like ribs and spines.
Collector and Display Significance
This specimen of Kosmoceras (Spinikosmoceras) transitionis is highly sought after due to its rarity, provenance, and striking features. Collectors appreciate it not only for its aesthetic appeal but also for its scientific importance as a biozone indicator within the Callovian. Its intricate shell structure and spine development make it a visually dramatic piece, perfect for display.
With its strong link to one of Normandy’s most famous fossil localities, this ammonite represents both a scientific treasure and a natural work of art.
Key Details
- Fossil Type: Ammonite
- Species: Kosmoceras (Spinikosmoceras) transitionis
- Age: Callovian, Middle Jurassic (c. 166 – 163 million years)
- Locality: Villiers-sur-Mer, France
- Distinctive ribbing and spine-like tuberculation
- Supplied with a Certificate of Authenticity
- The exact fossil shown in photographs will be sent
This rare Kosmoceras (Spinikosmoceras) transitionis ammonite fossil is a striking and scientifically significant specimen, offering collectors and enthusiasts the chance to own a genuine piece of Jurassic history from France’s classic Callovian deposits.
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