Asteroceras Fossil Ammonite Calcite Pair 2.5in Jurassic Dorset UK Stonebarrow Cliff Charmouth Lyme Regis Black Ven Marls

Description

Genuine Jurassic Ammonite from the Dorset Coast

Offered here is a striking 2.5 inch Asteroceras fossil ammonite, preserved as a calcite positive and negative pair, collected from the world-famous Black Ven Marls at Stonebarrow Cliff, Charmouth, part of the Jurassic Coast, Lyme Regis, Dorset, UK. This is a carefully selected, authentic British fossil that shows the actual specimen you will receive, exactly as photographed. The ammonite was discovered in situ by our own team members, Alister and Alison, on 25 January 2026, and has been professionally cleaned, prepared, and stabilised by Alison to ensure long-term preservation.

This fossil includes a lifetime Certificate of Authenticity on a generic card, guaranteeing it as a genuine natural specimen.

Species Overview – Asteroceras

Asteroceras is a classic and highly recognisable Early Jurassic ammonite, prized by collectors for its bold ribbing and broad, open coiling. Belonging to the Order Ammonitida, Superfamily Psiloceratoidea, and Family Arietitidae, Asteroceras represents an important stage in early ammonite evolution following the end-Triassic extinction.

This specimen dates to the Lower Lias (Lower Jurassic), Sinemurian Stage, specifically associated with the Asteroceras obtusum Biozone, making it both scientifically and stratigraphically significant.

Morphology and Preservation

This example displays the classic evolute shell form of Asteroceras, with earlier whorls clearly visible. The shell is characterised by:

• Strong, evenly spaced radial ribs
• A robust, rounded whorl section
• Clear symmetry and growth patterning

The fossil is preserved as a natural calcite replacement, common to the Black Ven Marls, where original aragonite shells dissolved and were later infilled by calcite. The result is a visually striking positive and negative split, showing both the external shell detail and its natural mould. This type of preservation is highly desirable, as it provides insight into both shell morphology and sediment interaction.

Geological and Depositional Context

The Black Ven Marls were deposited in a shallow, warm, epicontinental sea that covered much of southern Britain during the Early Jurassic. Fine-grained marls and periodic low-oxygen conditions created an ideal environment for ammonite preservation. These deposits are internationally renowned and form part of a UNESCO World Heritage Site, making fossils from this locality especially collectible.

Size, Authenticity, and Display

• Maximum diameter: approximately 2.5 inches (6.35 cm)
• Preservation: natural calcite positive and negative
• Preparation: cleaned, prepped, and treated by hand
• Authenticity: guaranteed genuine fossil with lifetime certificate

This fossil makes an excellent display piece, educational specimen, or addition to any serious ammonite or British fossil collection. Its manageable size allows for easy shelving, framing, or cabinet display while still retaining strong visual impact.

Ethical Collecting and Provenance

Collected responsibly and legally by experienced fossil hunters, this Asteroceras ammonite comes with full provenance and transparent discovery history. You will receive the exact specimen shown, not a stock example or similar piece, ensuring complete confidence in what you are purchasing.

A classic Dorset ammonite with real scientific heritage, this fossil is a tangible link to a Jurassic sea that existed nearly 195 million years ago.