Description
Fossil Ammonite – Arnioceras kridioides
Offered here is a fine fossil ammonite specimen of Arnioceras kridioides, a distinctive species from the Lower Sinemurian stage of the Early Jurassic (approximately 196–190 million years ago). This ammonite originates from classic deposits in France, a country renowned for its richly fossiliferous Jurassic strata. The specimen shown in the listing photographs is the exact piece you will receive. A 1 cm scale cube is provided for accurate sizing, and every purchase includes a Certificate of Authenticity, confirming the specimen as 100% genuine.
Geological Context
The Lower Sinemurian was part of the Early Jurassic, a time when shallow, warm seas covered much of Europe. France preserves some of the best exposures of these deposits, which belong to the Lias Group, a sequence of marine shales and limestones famous for their abundant ammonites. These sediments formed in calm, epicontinental seas, where muds and silts accumulated over time, entombing marine organisms that later fossilised under pressure.
Ammonites of the genus Arnioceras are especially important because they serve as biostratigraphic markers, helping geologists to subdivide the Sinemurian into finer zones. Their presence in the fossil record allows for precise dating and correlation between sites across Europe and beyond.
Scientific Classification
- Kingdom: Animalia
- Phylum: Mollusca
- Class: Cephalopoda
- Order: Ammonitida
- Superfamily: Psiloceratoidea
- Family: Arietitidae
- Genus: Arnioceras
- Species: Arnioceras kridioides
Morphological Features
Arnioceras kridioides is characterised by its planulate, laterally compressed shell, with relatively evolute coiling. The whorls are ornamented by sharp, radiating ribs that extend from the umbilicus to the venter, giving the ammonite a ribbed and well-defined appearance. The ribs are typically straight and evenly spaced, creating a distinctive visual pattern that is diagnostic of the species. The body chamber is relatively long, suggesting that this ammonite was adapted for an active swimming lifestyle in open marine waters.
Paleoenvironment and Ecology
This ammonite lived in shallow marine ecosystems, thriving in seas that supported a wide range of invertebrate life. As a member of the cephalopod group, Arnioceras kridioides would have been a fast-moving nektonic predator, feeding on small crustaceans, molluscs, and planktonic organisms. Its strong ribbing likely reinforced the shell against hydrostatic pressure, while the open coiling allowed for buoyancy control.
The Sinemurian seas of France were part of a broad, connected marine system extending across much of Europe. Ammonites like this one were widespread, yet individual species such as A. kridioides evolved rapidly, making them invaluable for scientific dating of the rock layers in which they are found.
Provenance and Authenticity
Collected from Jurassic deposits in France, this specimen is a carefully prepared and fully authentic fossil. It has been selected for its clarity of preservation, with diagnostic features that make it easily identifiable as Arnioceras kridioides. All our fossils are guaranteed genuine and are supplied with a Certificate of Authenticity for peace of mind and long-term value.
A Collector’s Fossil with Scientific Value
This Arnioceras kridioides ammonite is both a collector’s piece and a scientifically significant fossil, representing a key part of Early Jurassic ammonite faunas. Its rarity, fine ribbing, and provenance from France make it a particularly attractive addition to any fossil collection. Whether you are an amateur enthusiast, a professional paleontologist, or simply looking for a unique display piece, this ammonite embodies the beauty and history of life from nearly 200 million years ago.
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