Promicroceras Calcite Ammonite Fossil Black Ven Marls Lower Lias Jurassic Coast Black Ven Lyme Regis Dorset UK

Description

Authentic Promicroceras Calcite Ammonite Fossil

This striking Promicroceras Calcite Ammonite Fossil is an exceptional and genuine specimen from the Black Ven Marls, Lower Lias Formation, found along the Jurassic Coast at Black Ven, Lyme Regis, Dorset, UK. Dating from the Early Jurassic Period (approximately 195–200 million years ago), this fossil beautifully displays the intricate coiling and ribbing characteristic of the species Promicroceras planicosta, preserved naturally in translucent calcite.

Your specimen was discovered by our team members, Alister and Alison, on 13 September 2025, and has been carefully cleaned, prepped, and treated by Alison. The photograph shows the exact specimen you will receive, chosen for its exceptional clarity, preservation, and detail. Each piece we prepare is unique, representing a one-of-a-kind record of prehistoric marine life.

Geological Context and Origin

This fossil originates from the Black Ven Marls Member of the Charmouth Mudstone Formation, part of the Lower Lias Group on the UNESCO World Heritage Jurassic Coast. The cliffs of Lyme Regis and Charmouth are globally renowned for their fossil wealth and historical importance — the same strata famously studied and collected by early fossil hunter Mary Anning in the 19th century.

The Black Ven Marls were deposited in a low-energy, offshore marine environment, consisting primarily of soft, fine-grained muds and silts. These sediments accumulated under anoxic (oxygen-poor) conditions, which slowed decay and allowed for the exceptional preservation of marine organisms such as ammonites, belemnites, and marine reptiles. Over millions of years, mineral-rich groundwater percolated through the sediment, replacing the original shell material with calcite, resulting in this exquisite natural fossil.

This specimen dates to the Sinemurian Stage of the Early Jurassic and belongs to the Promicroceras planicosta Biozone, a key ammonite zone used by geologists worldwide for stratigraphic correlation.

Scientific Classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Subclass: Ammonoidea
• Order: Ammonitida
• Superfamily: Psiloceratoidea
• Family: Promicroceratidae
• Genus: Promicroceras
• Age: Early Jurassic (Sinemurian Stage)
• Formation: Black Ven Marls, Lower Lias
• Locality: Black Ven, Lyme Regis, Dorset, UK

As a representative of the genus Promicroceras, this fossil serves as an important index species, helping palaeontologists to identify and date Lower Jurassic strata across Europe.

Morphological Features and Preservation

This Promicroceras Calcite Ammonite displays the classic small, tightly coiled shell typical of the species, with all whorls visible and evenly ribbed. The ribs extend radially from the umbilicus to the outer edge of the shell, forming an elegant spiral pattern that exemplifies the symmetry of early ammonites. The shell is fully preserved in honey-toned calcite, allowing light to pass through in places and revealing delicate internal structure beneath the surface.

Fine ribbing across the shell’s whorls highlights its perfect preservation, and subtle mineral banding gives a natural shimmer under light. This calcite infill represents the slow crystallisation of calcium carbonate that replaced the original aragonite shell, locking in its minute features for eternity.

The matrix surrounding the ammonite consists of fine-grained marlstone from the Black Ven deposit, providing contrast and context to the fossil. The scale cube (1 cm) shown in the photograph offers accurate proportioning, and full measurements are available in the listing photos. This specimen has been professionally stabilised to preserve its natural texture and colouration.

Palaeobiological and Scientific Significance

Promicroceras ammonites were free-swimming cephalopods, distant relatives of modern squids, cuttlefish, and nautiluses. They lived in the warm, shallow seas that once covered much of what is now southern England. Their chambered shells, known as phragmocones, allowed them to regulate buoyancy through internal gas exchange, enabling agile movement as they hunted small crustaceans and plankton.

The species Promicroceras planicosta is one of the earliest true ammonites of the Jurassic, appearing soon after the end-Triassic mass extinction. Its abundance and widespread distribution make it a key fossil for dating the Sinemurian stage. The calcite preservation seen here is particularly prized among collectors because it captures the intricate structure of the ammonite while displaying a natural crystalline luster, merging scientific importance with visual beauty.

Fossils like this also help palaeontologists understand marine palaeoecology, evolutionary recovery, and sedimentary processes in early Jurassic ecosystems — revealing how life thrived in post-extinction seas.

Authenticity and Provenance

All of our fossils are 100% genuine specimens and come complete with a Certificate of Authenticity. Each piece is responsibly collected, professionally prepared, and carefully treated to ensure its long-term preservation. No replicas, restorations, or artificial enhancements are ever used — the fossil shown in the photographs is the actual specimen you will receive.

This Promicroceras Calcite Ammonite Fossil from Black Ven, Lyme Regis, Dorset is both a beautiful collector’s piece and a scientifically valuable specimen from Britain’s most famous fossil-bearing coastline — a timeless relic of the ancient seas that once covered the Jurassic world.