Description
Genuine Oppelia subradiata Ammonite Fossil
This carefully chosen fossil is a genuine Oppelia subradiata ammonite from Burton Bradstock in Dorset, UK. Dating from the Middle Bajocian interval of the Middle Jurassic, it represents an extinct marine cephalopod that inhabited the ancient seas covering southern Britain approximately 168 to 170 million years ago.
Oppelia subradiata is an elegant ammonite distinguished by its compressed shell, close coiling and comparatively delicate ornamentation. Its refined form contrasts with the broader, more heavily ribbed ammonites found in many other Middle Jurassic deposits, making it an attractive addition to a British fossil collection, ammonite display or geological teaching cabinet.
The photograph shows the actual fossil specimen you will receive. Its individual coiling, surface detail, preservation, colour, matrix and natural geological features can therefore be inspected before purchase. Full sizing and proportions can be seen in the accompanying photograph.
This authentic fossil includes a generic Certificate of Authenticity card with a lifetime guarantee.
Fossil Classification and Geological Details
Scientific name: Oppelia subradiata
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Haploceratoidea
Family: Oppeliidae
Geological period: Jurassic
Epoch: Middle Jurassic
Stage: Bajocian
Locality: Burton Bradstock, Dorset, UK
The species was originally described during the nineteenth century by the British naturalist and palaeontological illustrator James de Carle Sowerby. Oppelia subradiata later became the type species of the genus Oppelia, giving it particular importance in ammonite classification.
Oppeliid ammonites are valuable to palaeontologists because their shell shapes and ornamentation changed through Jurassic time. These evolutionary variations help specialists compare fossil-bearing strata and distinguish different marine faunas within the Middle Jurassic succession.
Oppelia Shell Shape and Fine Ornamentation
Oppelia subradiata possessed a planispirally coiled shell, meaning that its whorls developed in a single flat spiral around a central umbilicus. The shell is typically involute, with each outer whorl covering much of the preceding growth and leaving a relatively small central opening.
The whorls are laterally compressed, giving the ammonite a narrow and streamlined profile when viewed from the edge. Its flanks may appear gently convex or comparatively flat, narrowing towards the outer margin of the shell.
Fine, curved ribs can occur across the outer flanks, sometimes becoming clearer towards the ventrolateral area. These ribs are generally subtler than the strong, coarse ornamentation of many stephanoceratid ammonites. Faint growth lines may also record successive positions of the shell aperture as the animal developed.
The outer edge of the shell is known as the venter. In Oppelia, this area can be narrow and sharply defined, contributing to the ammonite’s elegant, hydrodynamic appearance. Umbilical width, whorl compression, rib curvature and ventral form are all features used when identifying oppeliid ammonites.
The amount of visible ornamentation depends upon the growth stage and preservation of the specimen. Natural fractures, worn areas, mineral deposits, attached matrix and incomplete sections are authentic characteristics produced during fossilisation and subsequent geological exposure.
Middle Jurassic Geology of Burton Bradstock
Burton Bradstock lies on Dorset’s internationally celebrated Jurassic Coast. The cliffs and coastal exposures preserve a sequence of sedimentary rocks that includes the Bridport Sand Formation and overlying fossil-bearing deposits of the Inferior Oolite Group.
During Middle Jurassic times, southern Britain was covered by a warm epicontinental sea connected to the wider marine basins of north-western Europe. Britain consisted of islands, submerged platforms and shallow seaways rather than one continuous landmass.
Sand, carbonate mud, shell debris and iron-rich sediment accumulated across the seabed. Changes in sea level, current strength, sediment supply and water depth produced a complex succession of marine beds. Some layers formed slowly and became condensed, concentrating fossils and mineral grains within relatively thin deposits.
The surrounding marine community included ammonites, belemnites, nautiloids, brachiopods, bivalves, gastropods, echinoids and crinoids. Fish and marine reptiles occupied higher levels within the ecosystem, while burrowing organisms lived within the soft seabed sediment.
Ammonites are especially important within these Dorset deposits because their comparatively rapid evolution enables geologists to place individual beds into a detailed chronological sequence. Their remains help correlate the Jurassic rocks of southern England with corresponding deposits elsewhere in Europe.
Life of an Oppelia Ammonite
Ammonites were marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. The animal occupied the final and largest part of its shell, known as the body chamber. Its head, eyes and tentacle-bearing soft body projected through the aperture.
The older coiled portion was divided into chambers by curved internal walls called septa. A narrow tube known as the siphuncle connected these chambers and helped regulate their liquid and gas content. This system provided buoyancy control and allowed the ammonite to maintain its position within the water column.
Movement was achieved through jet propulsion. Water was drawn into the mantle cavity and expelled through a muscular funnel, pushing the animal in the opposite direction. The compressed, streamlined shell of Oppelia subradiata suggests an ammonite adapted for efficient movement through open marine water.
Tentacles surrounding the mouth were probably used to capture small prey, collect food and investigate the environment. Its diet may have included planktonic organisms, small crustaceans and other marine animals.
Natural Fossilisation and Preservation
After death, the ammonite shell descended to the Jurassic seabed. Its soft tissues decayed while sediment entered and accumulated around the empty shell. Burial helped protect the remains from currents, scavengers and complete physical destruction.
Over millions of years, the surrounding sediment was compacted and cemented into rock. Mineral-rich groundwater could recrystallise, replace or dissolve the original aragonitic shell. Sediment filling the shell hardened into an internal mould that retained its coiled shape and impressions of the original ornamentation.
Where shell material disappeared, an external mould could preserve fine ribs, growth lines and other surface features. Natural mineral staining, surface wear, matrix attachments and small incomplete areas record the specimen’s individual history of burial, alteration, uplift and erosion.
This Oppelia subradiata ammonite is suitable for fossil collectors, ammonite enthusiasts, geology students and educational natural-history displays. The photograph shows the exact carefully selected specimen you will receive. Full sizing is shown in the photo. A generic Certificate of Authenticity card with a lifetime guarantee is included.
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