Description
Genuine Stephanoceras Ammonite with Belemnite Fossil
This carefully chosen fossil specimen features a genuine Stephanoceras sp. ammonite together with a belemnite, preserved from the Inferior Oolite Group at Burton Bradstock, Dorset, UK. Dating from the Middle Bajocian Stage of the Middle Jurassic, the specimen preserves the remains of two distinct types of extinct marine cephalopod that inhabited the warm seas covering southern Britain approximately 169 million years ago.
The abbreviation “sp.” indicates that the ammonite has been confidently identified to the genus Stephanoceras, while a precise species has not been assigned. This is standard scientific terminology for fossils that display the diagnostic characteristics of a genus but may be incomplete, partly concealed by matrix or lacking the features needed for reliable species-level identification.
The photograph shows the actual fossil specimen you will receive, including its natural shell detail, associated belemnite, surrounding matrix, colouration and individual preservation. Full sizing and scale information can be seen in the accompanying photograph.
Two Jurassic Cephalopods in One Specimen
This specimen is particularly appealing because it combines the remains of both an ammonite and a belemnite within the same piece of fossil-bearing rock. Although both animals belonged to the Cephalopoda, they possessed very different body forms.
Stephanoceras had an externally visible, planispirally coiled shell divided internally into chambers. The living animal occupied the final body chamber, while the older chambers formed the phragmocone and helped regulate buoyancy.
Belemnites had a more squid-like body and carried an internal skeleton. The part most commonly preserved is the solid, bullet-shaped guard or rostrum, which formed the rear section of the internal shell. The chambered phragmocone and delicate forward structures were less robust and are much less frequently preserved.
Finding both fossils together offers an attractive representation of the varied cephalopod life present in the Middle Jurassic sea. Their association also gives the specimen additional visual and educational interest for collectors of British marine fossils.
Stephanoceras Shell Form and Ornamentation
Stephanoceras is one of the best-known ammonite genera from the Bajocian. Members of the genus typically possessed robust, strongly ornamented shells with a relatively open central umbilicus, allowing portions of the earlier whorls to remain visible.
The shell commonly bears prominent primary ribs rising from the umbilical region. These ribs may strengthen into raised nodes or tubercles on the flanks before dividing into finer secondary ribs that continue towards and across the outer edge of the shell. This branching ornamentation gives Stephanoceras its characteristic sculptured appearance.
Whorl shape is generally rounded to broad rather than extremely compressed. Rib strength, spacing and tuberculation may change as the ammonite grows, meaning that the visible ornamentation can differ between juvenile and mature shell stages. Preservation, weathering and the amount of matrix covering the fossil also influence the detail visible on an individual specimen.
Inferior Oolite Group Geology
The Inferior Oolite Group is a highly fossiliferous sequence of Middle Jurassic marine rocks extending across parts of southern England. It includes oolitic limestones, sandy limestones, marls, iron-rich beds and condensed fossil horizons formed under changing shallow-marine conditions.
Oolitic limestone contains rounded carbonate grains called ooids. These formed when calcium carbonate accumulated in repeated coatings around tiny shell fragments or sediment particles moving through warm, agitated seawater. Over time, the grains settled, became compacted and were cemented together into limestone.
Sedimentation was frequently interrupted by changing sea levels, seabed erosion and strong currents. These processes could rework shells and concentrate fossil remains into particular horizons. Ammonites, belemnites, bivalves, brachiopods, gastropods and echinoids are among the marine organisms preserved within the Inferior Oolite succession.
Middle Bajocian Marine Environment
During the Middle Bajocian, Dorset lay beneath a shallow sea connected to the larger north-west European marine basin. The water supported diverse communities of free-swimming cephalopods and seabed-dwelling invertebrates.
Ammonites may have moved through different levels of the water column, using their chambered shells to help control buoyancy. Belemnites were active swimmers with streamlined bodies, arms and internal shells. Both were part of a complex marine food web containing predators, scavengers and smaller organisms.
Following death, their hard parts settled onto the seabed or were transported by currents. Burial within carbonate-rich sediment protected portions from destruction, allowing them to survive through millions of years of compaction, mineralisation and geological change.
Scientific Classification and Fossil Details
Fossil type: Ammonite with associated belemnite
Ammonite identification: Stephanoceras sp.
Ammonite family: Stephanoceratidae
Ammonite superfamily: Stephanoceratoidea
Ammonite order: Ammonitida
Belemnite group: Belemnitida
Geological period: Jurassic
Geological epoch: Middle Jurassic
Geological stage: Middle Bajocian
Geological unit: Inferior Oolite Group
Locality: Burton Bradstock, Dorset, United Kingdom
Natural Fossil Preservation
Any attached matrix, incomplete shell areas, mineral-filled sections, worn ribbing, fractures or variations in colour are natural characteristics of an authentic Jurassic fossil. The ammonite may preserve original or replaced shell material, an internal mould or a combination of both, while the belemnite is usually represented by its durable calcitic guard.
These features record the processes of burial, compaction, mineral replacement, erosion and eventual recovery from the host rock. Every naturally preserved fossil association is unique, giving this specimen its own arrangement of ammonite, belemnite and geological matrix.
Collectable Burton Bradstock Jurassic Fossil
This Stephanoceras ammonite with belemnite fossil would make an excellent addition to a collection of British fossils, Dorset ammonites, Bajocian fossils, Inferior Oolite specimens or prehistoric cephalopods. The association of two different cephalopod fossils makes it suitable for a natural history display, geological study collection, fossil cabinet, office or distinctive gift for a collector.
This is a 100% genuine fossil specimen and includes a Certificate of Authenticity generic card with a lifetime guarantee. The piece has been individually selected for its collectable qualities, and the photograph shows the exact specimen that will be supplied.
Full sizing please see photo.
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