Arnioceras Fossil Ammonite Jurassic Coast Charmouth Lyme Regis Dorset UK

Description

Arnioceras Fossil Ammonite from Dorset

This listing features a genuine Arnioceras fossil ammonite from the Black Ven Marls, Lower Lias Formation, Stonebarrow Cliff, Charmouth, Lyme Regis, Dorset, UK, part of the celebrated Jurassic Coast World Heritage Site. This specimen dates to the Early Jurassic (Sinemurian stage, around 199–196 million years ago) and represents one of the most iconic ammonite genera of the Lower Jurassic. The fossil was discovered by our own team members, Alister and Alison, on 14th September 2025, and was then cleaned, prepped, and treated by Alison to reveal its full natural detail and ensure long-term preservation.

Geological Setting – Black Ven Marls

The Black Ven Marls are globally renowned for their fossil richness, yielding ammonites, crinoids, belemnites, and marine reptiles. These marls and shales were deposited in a shallow marine environment, where fine sediments buried organisms quickly after death, allowing for remarkable preservation. The Jurassic Coast cliffs at Charmouth and Lyme Regis have produced scientifically important fossils for centuries, inspiring generations of naturalists and continuing to provide outstanding specimens today.

Species Profile – Arnioceras

The genus Arnioceras belongs to the Order Ammonitida, Superfamily Psiloceratoidea, and Family Arietitidae. These ammonites are characterised by their evolute shells, in which all whorls are clearly visible, and their bold, radiating ribbing. The ribs often bifurcate, adding to their distinctive ornamentation, and give the shell a strong and recognisable form. Arnioceras ammonites were nektonic predators, active swimmers in the Early Jurassic seas, preying on smaller marine invertebrates. Their distinctive rib patterns make them particularly desirable to collectors.

Morphology and Preservation

This specimen shows the classic features of Arnioceras ammonites, with its clearly exposed whorls and bold ribbing extending from the umbilicus to the outer shell. The preservation within the marl matrix highlights the strong structural features, allowing both collectors and paleontologists to appreciate the ammonite’s natural design. Specimens from the Black Ven Marls often display excellent surface detail due to the fine-grained sediment in which they were preserved. This example demonstrates the robust shell structure typical of the genus, making it an attractive and scientifically useful fossil.

Stratigraphic and Scientific Importance

Arnioceras is a key index fossil for the Lower Sinemurian stage, specifically within the Arnioceras semicostatum biozone. These fossils are critical for biostratigraphy, allowing geologists to correlate Jurassic rock formations across Europe with precision. The genus is significant in studies of ammonite evolution following the Triassic–Jurassic extinction event, marking the diversification and success of ammonites during the Early Jurassic. Fossils such as this provide both scientific insight and a tangible link to deep geological time.

Ethical Discovery and Expert Preparation

This specimen was responsibly collected by our team at Stonebarrow Cliff and prepared by Alison using careful and ethical techniques to preserve the ammonite’s features. This ensures that the fossil retains both its natural authenticity and display quality. Supporting ethical collecting helps protect the heritage of the Jurassic Coast while making rare and important specimens available to collectors.

Authenticity and Presentation

All of our fossils are 100% genuine specimens and are supplied with a Certificate of Authenticity. The photographs show the exact specimen you will receive, not a stock image. For precise sizing, a 1 cm scale cube is shown in the photos. The fossil has been selected for its quality and visual appeal, making it an excellent choice for collectors, educators, or display in any natural history setting.

This Arnioceras fossil ammonite from the Black Ven Marls of Charmouth, Lyme Regis, Dorset, UK, is a fine example of an Early Jurassic ammonite, combining scientific importance, striking morphology, and historical provenance from the famous Jurassic Coast.