Arnioceras and Promicroceras Ammonite Fossil Jurassic Lyme Regis Dorset

Description

Authentic Arnioceras and Promicroceras Ammonite Fossil from the Jurassic Coast

Presented here is a genuine dual ammonite fossil featuring Arnioceras and Promicroceras, collected from the classic Black Ven Marls at Stonebarrow Cliff, Charmouth, Lyme Regis, Dorset, UK. This world-renowned stretch of coastline forms part of the UNESCO-listed Jurassic Coast, celebrated internationally for its continuous and scientifically important Early Jurassic fossil record. The specimen has been carefully selected to showcase both ammonite genera preserved together, offering a visually striking and scientifically informative piece. The photographs show the exact fossil you will receive, and full sizing details are provided in the photos for complete clarity.

This fossil is a 100% genuine specimen and includes a Certificate of Authenticity lifetime guarantee generic card, ensuring long-term confidence in provenance and authenticity.

Geological Formation and Age

The specimen originates from the Lower Lias Group, deposited during the Early Jurassic Period, approximately 199–191 million years ago, within the Sinemurian Stage. The Black Ven Marls are composed of fine-grained marine mudstones and marls laid down in a shallow epicontinental sea that covered southern Britain. Stonebarrow Cliff is one of the most productive Lower Jurassic localities in Europe and is particularly important for ammonite biostratigraphy, making fossils from this horizon highly desirable.

Fossil Type, Species, and Scientific Context

This specimen contains two distinct ammonite genera: Arnioceras and Promicroceras, both belonging to the Order Ammonitida and the Family Arietitidae. These genera are characteristic of the Lower Lias and are widely used in Early Jurassic zonation.

Arnioceras is typically associated with the lower Sinemurian and is recognised for its robust shell form and strong ribbing. Promicroceras, often smaller and more finely ribbed, represents an early evolutionary stage within the arietitid ammonites. The association of both genera on a single specimen provides an excellent snapshot of Early Jurassic ammonite diversity and evolutionary development.

Morphology and Notable Features

The ammonites display classic planispiral coiling, with clear differentiation between the two genera. Arnioceras shows broader whorls with pronounced ribbing, while Promicroceras exhibits tighter coiling and finer ornamentation. Growth lines and rib patterns are visible, allowing appreciation of natural ontogenetic changes. Preservation quality enables the shell morphology of both ammonites to be clearly observed, making this specimen both visually engaging and educationally valuable.

Depositional Environment

During the Early Jurassic, the Charmouth and Lyme Regis region lay beneath a warm, shallow marine sea rich in ammonites, belemnites, bivalves, echinoderms, and early marine reptiles. Fine sediments accumulated slowly on the sea floor, periodically burying shells soon after death. These low-energy conditions promoted fossilisation and resulted in the excellent preservation seen in the Black Ven Marls. The presence of multiple ammonites on a single piece reflects episodic burial events within this ancient marine environment.

Collecting, Display, and Educational Value

This Arnioceras and Promicroceras ammonite fossil is ideal for serious fossil collectors, educational collections, museum-style displays, or refined interior presentation. The combination of two stratigraphically significant ammonite genera on one specimen adds considerable scientific and visual interest. Fossils from Stonebarrow Cliff are increasingly sought after due to their provenance and research importance. Each specimen we offer is individually selected to ensure you receive an authentic and well-presented example of Early Jurassic marine life from one of the world’s most celebrated fossil coastlines.