Oistoceras Fossil Ammonite Lower Lias Jurassic Coast Charmouth Dorset UK Green Ammonite Beds Stonebarrow

Authentic Microderoceras Fossil Ammonite from the Jurassic Coast, Dorset

This exceptional Microderoceras Fossil Ammonite originates from the world-famous Black Ven Marls of the Lower Lias Formation, part of the Jurassic Coast near Black Ven, Lyme Regis, Dorset, UK. Discovered by our own fossil hunters Alister and Alison on 02 November 2025, the specimen represents an authentic and scientifically significant piece of Early Jurassic history, approximately 195–200 million years old. Carefully cleaned, prepped, and treated by Alison, this ammonite has been preserved with remarkable precision, revealing exquisite shell details and natural patterns that make it ideal for both collectors and educational display.

Geological and Scientific Context

The Microderoceras belongs to the family Eoderoceratidae, within the superfamily Eoderoceratoidea, a group of early ammonites from the order Ammonitida. These cephalopods thrived during the Sinemurian Stage of the Early Jurassic period. The Black Ven Marls—famous among palaeontologists and collectors alike—form part of the Charmouth Mudstone Formation, a richly fossiliferous sequence of clays and marls deposited in shallow marine conditions along the ancient Jurassic coastline. The slow accumulation of fine sediments created a low-oxygen environment that allowed delicate fossils, such as ammonites, to be preserved in remarkable three-dimensional detail.

Microderoceras is particularly important in stratigraphy, as species within this genus define the Microderoceras Biozone, used internationally to correlate Sinemurian marine strata. Its abundance, wide distribution, and easily recognisable form make it a key guide fossil for dating early Jurassic deposits across Europe and beyond.

Morphology and Distinctive Features

The Microderoceras ammonite is instantly recognisable by its tight, evolute coiling, with all whorls visible and evenly spaced. The shell displays strong radial ribs and distinct spines or tubercles along the outer edge, giving it a striking, ornamental appearance. These spines likely served hydrodynamic or defensive functions during its life in the Jurassic seas. The ribbing and sculpture of the shell also reveal adaptations to a nektonic lifestyle, meaning this animal swam actively through open water, using jet propulsion similar to modern cephalopods.

This particular specimen shows excellent preservation of the ribbed whorls and outer keel, with the natural marl matrix offering a beautiful contrast to the fossilised shell. The delicate ribbing and characteristic ventral groove—hallmarks of the genus—are clearly visible, making it an outstanding example of its type. Its compact yet detailed structure encapsulates the early evolutionary experimentation of ammonites following the end-Triassic extinction.

Formation, Age, and Depositional Environment

The Black Ven Marls date to the lower part of the Sinemurian Stage, approximately 197 million years ago, and are composed mainly of soft grey marls and mudstones rich in calcite and iron pyrite. These sediments were deposited in a calm, low-energy marine shelf environment, part of the extensive shallow seas that once covered Dorset during the Jurassic. Occasional storm events buried organic material quickly, leading to exceptional fossil preservation. The Black Ven landslip area is one of the most productive fossil localities in the world, yielding thousands of ammonites, belemnites, and marine reptile remains.

Preparation and Provenance

This specimen was discovered and prepared entirely by our in-house UK team, ensuring a fully traceable provenance and professional preparation. Alison’s careful mechanical cleaning and conservation work preserve the ammonite’s natural detail while maintaining its geological authenticity. The fossil’s surface has been gently stabilised to ensure long-term durability without altering its natural appearance. Every fossil we sell is 100% genuine and accompanied by a Certificate of Authenticity, confirming its identity, locality, and preparation history.

Size and Presentation

Scale cube = 1 cm. Please refer to the listing photographs for exact sizing. The images show the actual specimen you will receive. Its natural matrix provides a stable base, making it ideal for display in a collection, educational setting, or as a decorative natural history feature. The piece’s unique preservation and scientific significance make it both a collectible and a conversation piece.

A Rare Collector’s Specimen from the Heart of the Jurassic Coast

Specimens of Microderoceras from the Black Ven Marls are highly sought after for their aesthetic ribbing, rarity, and scientific importance. This fossil not only represents a genuine piece of Britain’s geological heritage but also captures a moment in time from the early evolution of the ammonites. Expertly prepared and preserved, it stands as a testament to the natural artistry and enduring fascination of the Jurassic seas.