Microderoceras Fossil Ammonite Macroconch with Two Microconches Jurassic Coast Dorset UK

Description

Microderoceras Fossil Ammonite – A Rare Multi-Specimen Find

This listing is for a remarkable Microderoceras fossil ammonite specimen, featuring a macroconch with two accompanying microconches, from the Black Ven Marls, Lower Lias Formation, Stonebarrow Cliff, Charmouth, Lyme Regis, Dorset, UK. Dating back to the Early Jurassic (Sinemurian stage, approximately 199–196 million years ago), this rare association beautifully illustrates the natural variation within ammonite populations. Discovered by our team members Alister and Alison on 14th September 2025, it has been expertly cleaned, prepped, and treated by Alison to reveal its fine structural and morphological details.

Geological Context – Black Ven Marls, Jurassic Coast

The Black Ven Marls are part of the Lower Lias deposits of the Dorset coast, a region recognised as a UNESCO World Heritage Site for its extraordinary fossil content. These sedimentary layers were formed in a shallow marine environment, preserving an abundance of ammonites, belemnites, crinoids, and marine reptiles. The conditions of deposition allowed for the exquisite preservation of ammonites, many of which display their intricate ribbing and coiling in stunning detail. Fossils collected from Stonebarrow Cliff are highly regarded by collectors and paleontologists alike, offering insights into the biodiversity and ecosystems of the Early Jurassic seas.

Species Profile – Microderoceras

The genus Microderoceras belongs to the Order Ammonitida, Superfamily Eoderoceratoidea, and Family Eoderoceratidae. This genus is particularly distinctive due to its ribbed, evolute shells with widely exposed whorls. The ribs are strong, radiating boldly across the whorls, giving the shell a spiny appearance when well-preserved. The difference between macroconchs (larger forms, thought to be female) and microconchs (smaller forms, thought to be male) illustrates sexual dimorphism within ammonites, a fascinating feature of their biology. The presence of both morphotypes together in this specimen highlights their life association and evolutionary adaptations.

Morphology and Distinctive Features

This fossil preserves one large macroconch ammonite alongside two smaller microconchs, making it a rare and scientifically valuable multi-specimen block. The macroconch shows broad, open coiling with strong ribs running across the shell, while the microconchs exhibit the same general ornamentation but on a reduced scale, reflecting their different roles within the species. The preservation in fine marl matrix has captured these morphological details with clarity, offering an excellent teaching and display piece for understanding ammonite dimorphism and population structures.

Scientific and Stratigraphic Importance

Microderoceras is a key genus for the Sinemurian stage, particularly within the Microderoceras biozone, making it an important tool for biostratigraphy. Its abundance and distinctive morphology have long made it a focus of paleontological research. Specimens displaying both macroconchs and microconchs together are of special interest, as they illustrate the reproductive biology and natural pairing of ammonite dimorphs. Such fossils provide not only aesthetic appeal but also scientific depth, offering evidence of Early Jurassic evolutionary patterns and ecological strategies.

Ethical Discovery and Skilled Preparation

This fossil was responsibly collected on the foreshore at Stonebarrow Cliff and prepared by Alison using precision tools and careful conservation techniques. Ethical collecting ensures the continued preservation of this World Heritage Site, while professional preparation brings out the fossil’s natural details without compromising its authenticity.

Authenticity and Presentation

All of our fossils are 100% genuine specimens and are accompanied by a Certificate of Authenticity. The photographs show the exact specimen you will receive, not a stock image. A 1 cm scale cube is included in the images to provide accurate size reference. This specimen was carefully chosen for its exceptional preservation and its unusual combination of macroconch and microconchs, making it an outstanding piece for collectors, educators, and natural history enthusiasts.

This Microderoceras fossil ammonite with a macroconch and two microconches from the Black Ven Marls, Charmouth, Lyme Regis, Dorset, UK, is a scientifically important and visually striking specimen that captures the diversity and evolutionary adaptations of ammonites in the Early Jurassic seas.