Stephanoceras umbilicum Ammonite Fossil Lower Bajocian Jurassic Sherbourne Dorset UK – Alice Purnell Collection with COA

Stephanoceras umbilicum Ammonite Fossil – Lower Bajocian, Jurassic, Sherbourne, Dorset, United Kingdom

This remarkable Stephanoceras umbilicum ammonite fossil is an authentic and beautifully preserved specimen from the Lower Bajocian Stage of the Middle Jurassic, discovered near Sherbourne, Dorset, England. It comes from the renowned Alice Purnell Collection, a scientifically respected source of high-quality, well-documented British Jurassic fossils. The photo shows the exact specimen you will receive, and the scale cube equals 1cm for accurate sizing. This piece exemplifies the rich palaeontological heritage of Dorset’s Jurassic formations and offers a unique connection to the ancient seas of 170 million years ago.

Geological Setting and Age

This specimen originates from Lower Bajocian deposits within the Inferior Oolite Group, exposed in the Sherbourne area of Dorset, part of the classic Wessex Basin geological province. The Bajocian represents an interval within the Middle Jurassic Period, approximately 170–168 million years ago, when southern England was submerged beneath a warm, shallow, tropical sea.

These conditions favoured the development of carbonate-rich marine environments where organisms such as ammonites, belemnites, brachiopods, and echinoids thrived. Periodic sedimentation of fine oolitic limestones and calcareous muds provided ideal circumstances for the fossilisation of marine life. Stephanoceras umbilicum would have lived in this tranquil sea, swimming freely in the upper water column as an agile predator.

Scientific Classification

• Kingdom: Animalia

• Phylum: Mollusca

• Class: Cephalopoda

• Order: Ammonitida

• Superfamily: Stephanoceratoidea

• Family: Stephanoceratidae

• Genus: Stephanoceras

• Species: Stephanoceras umbilicum (Sowerby, 1816)

• Geological Stage: Lower Bajocian (Middle Jurassic)

• Locality: Sherbourne, Dorset, United Kingdom

This species was first described by James Sowerby (1816), one of Britain’s pioneering naturalists and illustrators, whose contributions to palaeontology laid the foundation for modern ammonite taxonomy. Stephanoceras is the type genus for the superfamily Stephanoceratoidea, representing a key evolutionary lineage in Jurassic ammonite development.

Morphology and Diagnostic Features

The genus Stephanoceras is famed for its large, ornate shells and bold ribbing — features that make specimens such as this both scientifically valuable and visually striking. This specimen of Stephanoceras umbilicum displays the classic involute coiling typical of the genus, with only a narrow portion of the inner whorls visible around the umbilicus.

The flanks of the shell are marked by strong, bifurcating ribs that arise from the umbilical shoulder and curve gently forward toward the venter (outer edge). These ribs often terminate in low tubercles or swellings before crossing the venter smoothly, indicating a robust yet hydrodynamically refined form. The whorls are broad and slightly compressed, while the suture lines — where the internal chamber walls meet the shell — show complex lobes and saddles characteristic of ammonites in this family.

The combination of bold ribbing, symmetry, and planispiral form exemplifies the high degree of morphological adaptation achieved by Stephanoceras. These features not only enhanced the shell’s strength but also likely played a hydrodynamic role in stability and manoeuvrability within the Jurassic seas.

Palaeoenvironment and Biozone Context

This specimen likely belongs to the Humphriesianum Zone, a key ammonite biozone within the Lower Bajocian stratigraphy. This zone is globally significant and is used to correlate Jurassic marine sequences across Europe. It is characterised by abundant Stephanoceras and related ammonites such as Normannites and Garantiana.

The depositional environment at Sherbourne during this time was part of a broad, shallow, epicontinental sea. Sedimentological evidence indicates clear, warm, and well-oxygenated waters that supported rich marine biodiversity. The oolitic limestones of the Inferior Oolite are composed of tiny spherical grains (ooids) formed by chemical precipitation in these calm conditions. Fossils such as Stephanoceras umbilicum were preserved when their shells were buried rapidly in fine carbonate sediments, protecting them from scavengers and decay.

Such environments capture a moment in geological history when southern Britain lay close to the equator, forming part of the northern margin of the Tethys Ocean — a region renowned for its remarkable fossil record and evolutionary innovations among cephalopods.

Provenance – The Alice Purnell Collection

This ammonite comes from the highly respected Alice Purnell Collection, built through decades of fieldwork and study across key Jurassic sites in Britain. Fossils from this collection are recognised for their scientific reliability, precise locality data, and careful preparation. Each specimen is professionally conserved and catalogued, preserving its geological context and aesthetic quality. Collectors and institutions prize pieces from this collection for their authenticity and their value as reference specimens.

Authenticity and Presentation

All of our fossils are 100% genuine specimens and come with a Certificate of Authenticity, confirming their identity, geological age, and provenance. The photo shows the exact specimen you will receive, with a 1cm scale cube for accurate size reference. This piece has been carefully selected and inspected to ensure it meets museum-grade standards for preservation and scientific integrity.

A Classic British Jurassic Ammonite

This Stephanoceras umbilicum from Sherbourne, Dorset, represents a superb example of the Lower Bajocian ammonite fauna of southern England. Its detailed ribbing, elegant coiling, and outstanding provenance make it both an object of scientific interest and a striking collector’s display piece. Discovered within the world-renowned Jurassic formations of Dorset and preserved in the Alice Purnell Collection, this ammonite embodies the beauty and history of Britain’s ancient marine world — a timeless relic from the age of the dinosaurs, formed over 170 million years ago.