Xipheroceras Fossil Ammonite Full Calcite Lyme Regis Jurassic Coast Dorset UK Genuine Specimen with Certificate

Xipheroceras Fossil Ammonite – Full Calcite Replacement, Lyme Regis

This exceptional Xipheroceras fossil ammonite from the Black Ven Marls of the Lower Lias at Stonebarrow Cliff, Charmouth, Lyme Regis, Dorset, UK, is preserved in full calcite replacement. The specimen was discovered by our own team members, Alister and Alison, on 28 February 2025 and has been carefully cleaned, prepped and treated by Alison to ensure outstanding presentation while maintaining its natural geological integrity.

This fossil includes a Certificate of Authenticity lifetime guarantee generic card. The photographs show the exact specimen you will receive, and full sizing details are clearly provided in the listing images.

Fossil Identification and Classification

Xipheroceras is an Early Jurassic ammonite belonging to:

• Order: Ammonitida

• Suborder: Ammonitina

• Superfamily: Eoderoceratoidea

• Family: Eoderoceratidae

This genus is characteristic of the Sinemurian Stage of the Lower Jurassic, dating to approximately 199–190 million years ago. Xipheroceras species are commonly associated with Lower Lias ammonite biozones that allow precise stratigraphic dating of the Dorset coast sequence.

Ammonites such as Xipheroceras are important index fossils due to their rapid evolutionary changes and wide geographic distribution. Their presence within the Black Ven Marls provides crucial information for correlating Jurassic marine strata.

Geological Context – Black Ven Marls, Lower Lias

The Black Ven Marls form part of the Lower Lias Group, deposited in a shallow marine environment during the Early Jurassic. These dark clays and marls accumulated in relatively low-energy offshore conditions, allowing fine sediment to settle and bury marine organisms rapidly.

Stonebarrow Cliff and the wider Lyme Regis area form part of the UNESCO World Heritage Jurassic Coast, internationally recognised for its continuous geological record spanning the Triassic to Cretaceous periods. The Lower Lias sequence here is particularly renowned for ammonites, belemnites, bivalves, and marine reptiles.

Full Calcite Preservation

This specimen is preserved in full calcite replacement, meaning the original aragonitic shell material has been replaced by calcite during diagenesis. After burial, mineral-rich groundwater percolated through the sediment, gradually replacing the shell structure with crystalline calcite while retaining the original morphological detail.

Full calcite ammonites are especially attractive due to their crystalline structure, often displaying a subtle sparkle and enhanced durability compared to unmineralised shell remains. The calcite preservation also reflects the complex geochemical processes that occurred within the Lower Lias sediments after burial.

Morphology and Notable Features

Xipheroceras ammonites typically display an evolute coiling pattern, where earlier whorls remain visible rather than tightly enclosed. The shell exhibits strong ribbing across the flanks, often bifurcating as ribs approach the outer whorl.

The rib structure, whorl shape, and overall shell geometry are key identifying features within the Eoderoceratidae family. In calcite-preserved examples, these morphological traits can be sharply defined, providing excellent visual clarity of Jurassic shell architecture.

Discovery, Preparation and Authenticity

This fossil was personally discovered by Alister and Alison on 28 February 2025 along Stonebarrow Cliff. Following recovery, Alison carefully prepared and stabilised the specimen, ensuring the calcite preservation and natural matrix context were retained.

This Xipheroceras Fossil Ammonite is a genuine Jurassic Coast specimen and includes a Certificate of Authenticity lifetime guarantee generic card. The fossil shown in the photographs is the exact piece you will receive, selected for its preservation quality, locality significance, and full calcite mineralisation.

A fully calcitised Xipheroceras from the Black Ven Marls represents a remarkable example of Early Jurassic marine life and post-depositional mineral transformation, combining palaeontological importance with striking crystalline preservation from one of the world’s most famous fossil coastlines.