Description
Genuine Chondroceras gervillei Ammonite Fossil
This carefully chosen fossil is a genuine Chondroceras gervillei ammonite from the Inferior Oolite Group at Burton Bradstock, Dorset, UK. It dates from the Lower Bajocian Stage of the Middle Jurassic, representing an extinct marine cephalopod that lived in the warm seas covering southern Britain approximately 170 million years ago.
The listing photograph shows the actual fossil specimen you will receive, allowing its natural shell form, ribbing, matrix, colouration and individual preservation to be examined before purchase. This is not a representative stock image. Full sizing and scale information can be seen in the accompanying photograph.
Lower Bajocian Jurassic Ammonite
The Bajocian Stage forms part of the Middle Jurassic and records an important period of ammonite diversification. During the Lower Bajocian, the area that is now Dorset lay beneath a shallow marine environment connected to the wider north-west European sea.
These waters supported abundant marine life, including ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids and other invertebrates. Ammonites were especially successful and developed a wide variety of shell forms, rib patterns and whorl proportions.
Because ammonites evolved relatively rapidly and were distributed across extensive marine areas, their fossils are valuable for dating and correlating Jurassic rocks. Distinctive ammonite assemblages allow geologists to divide the Bajocian succession into detailed biozones and subzones, helping reconstruct the geological history of Dorset and comparable European localities.
Chondroceras Shell Form and Ornamentation
Chondroceras is a distinctive genus of Bajocian ammonite known for its compact, robust and strongly ornamented shell. The shell is planispirally coiled, meaning that it grew around a central umbilicus within a single plane.
Members of the genus commonly display broad, inflated whorls and a relatively deep or open umbilical region. Strong primary ribs originate near the umbilicus and extend across the flanks. These may divide into secondary ribs as they approach the outer portion of the shell, producing a pronounced sculptural pattern.
Raised swellings or tubercles may occur where the primary ribs branch. The outer margin, known as the venter, is generally broad and rounded, with the secondary ribbing continuing across it. This combination of inflated whorls, strong ribs and branching ornamentation gives Chondroceras a recognisable and substantial appearance.
Visible shell details can vary with the ammonite’s growth stage. Juvenile whorls may display denser or finer ribbing, while later growth can produce broader ribs and changing whorl proportions. Fossilisation, natural weathering and the amount of matrix present may also influence how much of the original ornamentation remains visible.
Inferior Oolite Group Geology
The Inferior Oolite Group is a fossil-rich Middle Jurassic rock succession found across southern England. It contains oolitic limestone, sandy limestone, marl, iron-rich beds and condensed fossil horizons deposited under changing shallow-marine conditions.
Oolitic limestone is composed partly of small rounded carbonate grains known as ooids. These formed when calcium carbonate built up in repeated layers around tiny shell fragments or sediment particles moving through warm, agitated seawater. The grains later settled, became compacted and were cemented together into limestone.
Deposition within the Inferior Oolite sea was often interrupted by changes in sea level, currents, erosion and periods of very slow sediment accumulation. Fossil shells could remain exposed on the seabed, become reworked and eventually collect within concentrated horizons. These processes contributed to the rich and varied ammonite assemblages for which the Inferior Oolite is known.
Burton Bradstock Fossil Locality
Burton Bradstock lies along the Jurassic Coast of west Dorset, an area internationally recognised for its exposed Mesozoic geology and important fossil record. The cliffs and surrounding inland deposits preserve marine sediments laid down during several stages of the Jurassic Period.
The Inferior Oolite rocks associated with Burton Bradstock record a shallow sea with changing energy levels and sedimentary conditions. Fossils from the locality provide evidence of the marine ecosystems that occupied the Dorset region during the early Middle Jurassic.
Ammonites from this succession are especially sought after because they combine scientific interest, distinctive shell ornamentation and a documented British locality. A specimen of Chondroceras gervillei offers a tangible connection to the ancient Jurassic sea and to Dorset’s long tradition of palaeontological collecting.
Scientific Classification and Fossil Details
Fossil type: Ammonite
Scientific name: Chondroceras gervillei
Family: Sphaeroceratidae
Superfamily: Stephanoceratoidea
Order: Ammonitida
Geological period: Jurassic
Geological epoch: Middle Jurassic
Geological stage: Lower Bajocian
Geological unit: Inferior Oolite Group
Locality: Burton Bradstock, Dorset, United Kingdom
The family Sphaeroceratidae includes robust Jurassic ammonites with compact coiling, inflated whorls and strong ornamentation. These shell characteristics make members of the family visually distinctive and useful when studying Bajocian ammonite evolution.
Ammonite Biology and Chambered Shell
The living ammonite occupied the final and largest section of its shell, known as the body chamber. Earlier parts of the shell were divided by internal walls called septa into a series of chambers forming the phragmocone.
These chambers contained controlled quantities of liquid and gas, allowing the animal to regulate buoyancy within the water column. The chamber divisions met the outer shell along complex lines known as sutures, which can sometimes become visible when the shell surface is removed or naturally weathered.
Ammonites belonged to the cephalopods and were related to living squid, cuttlefish, octopuses and nautiluses. They were highly successful inhabitants of Mesozoic seas before becoming extinct at the end of the Cretaceous Period.
Natural Fossil Preservation
After the ammonite died, its shell settled onto the Jurassic seabed or was moved by currents before burial. Sediment gradually covered the shell, while mineral-rich groundwater and geological pressure transformed the surrounding deposits into rock.
The original shell material may have been preserved, mineralised, replaced or dissolved, leaving a natural internal mould. Many ammonites preserve a combination of altered shell material and sediment-filled internal chambers.
Any attached matrix, incomplete sections, worn ribs, minor fractures, mineral-filled areas or variations in colour are natural geological characteristics. These features record the processes of burial, compaction, fossilisation, exposure and recovery and make every authentic fossil specimen unique.
Collectable Dorset Jurassic Fossil
This Chondroceras gervillei ammonite would make an excellent addition to a collection of British fossils, Dorset ammonites, Lower Bajocian fossils, Inferior Oolite specimens or prehistoric cephalopods. Its strong ornamentation and documented geological origin also make it suitable for a natural history display, fossil cabinet, educational collection, office or distinctive gift for a fossil enthusiast.
This is a 100% genuine fossil specimen and includes a Certificate of Authenticity generic card with a lifetime guarantee. The fossil 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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