Promicroceras Ammonite Fossil Split Nodule Calcite Lyme Regis Dorset UK Lower Lias Jurassic Coast Positive Negative Pair Authentic

Description

Promicroceras Calcite Ammonite Split Nodule – Positive and Negative Pair from Lyme Regis

This exceptional Promicroceras ammonite fossil is preserved as a classic positive and negative split nodule, revealing both sides of the original shell impression in stunning detail. Sourced from the Black Ven Marls of the Lower Lias on the Jurassic Coast at Black Ven, Lyme Regis, Dorset, UK, this specimen offers both scientific value and striking visual appeal. The fossil shown in the photographs is the exact specimen you will receive, carefully selected for its clarity, preservation, and completeness.

Geological Age & Formation

This fossil dates to the Early Jurassic period, specifically the Sinemurian stage, approximately 190–199 million years ago. The Black Ven Marls are among the most productive fossil-bearing deposits in the UK, formed in a shallow marine environment where fine sediments allowed exceptional preservation. Promicroceras is strongly associated with the Promicroceras planicosta Biozone, a key stratigraphic marker used to define Lower Lias sequences.

Taxonomy & Classification

• Order: Ammonitida
• Superfamily: Psiloceratoidea
• Family: Arietitidae
• Genus: Promicroceras

Promicroceras is one of the most recognisable ammonites of the Early Jurassic, widely studied and first described by Hyatt. It represents an important stage in ammonite evolution following the end-Triassic extinction.

Morphology & Positive-Negative Preservation

This specimen beautifully demonstrates the classic planispiral coiling of ammonites, with well-defined whorls and distinct ribbing across the shell. The ribs are fine to moderately strong and radiate outward, often becoming more pronounced toward the outer whorls. These features are clearly visible across both halves of the split nodule.

The positive and negative split provides a complete view of the fossilisation process. One half preserves the raised external form of the ammonite, while the opposing half displays the corresponding impression. This dual perspective makes the specimen particularly desirable for both collectors and educational use.

The calcite preservation enhances the fossil’s appearance, with subtle crystalline textures adding depth and visual interest under light.

Depositional Environment

The Black Ven Marls were deposited in a relatively low-energy marine setting, allowing fine sediments to settle around organic remains. Periodic low-oxygen conditions reduced decay and scavenging, leading to exceptional preservation. Nodules formed around organic material, protecting fossils such as this ammonite and preserving them in remarkable detail.

Discovery & Expert Preparation

This fossil was discovered by our experienced team members, Alister and Alison, along the Jurassic Coast. Following careful extraction, the nodule was expertly split, revealing the ammonite within. Alison then cleaned, stabilised, and prepared both halves to enhance visibility while maintaining the natural integrity of the specimen.

Authenticity & Provenance

This is a genuine Promicroceras ammonite fossil and includes a Certificate of Authenticity with a lifetime guarantee. All specimens are responsibly sourced and professionally prepared, ensuring confidence in both authenticity and provenance.

Display & Collectability

Split ammonite nodules are highly sought after due to their educational and aesthetic appeal. The ability to display both positive and negative halves makes this specimen ideal for collectors, educators, and fossil enthusiasts. Its origin from Lyme Regis, part of the UNESCO-listed Jurassic Coast, further enhances its desirability and historical significance.

Condition & Sizing

Please refer to the photographs for full sizing and condition details, as they form part of the description. This is a carefully chosen specimen, and the images accurately represent the exact fossil you will receive.