Description
Genuine Darellia recticostata Ammonite Fossil
This carefully chosen fossil is a genuine Darellia recticostata ammonite from Sherborne, Dorset, UK. It is recorded from the Bajocian Stage of the Middle Jurassic, representing an extinct marine cephalopod from the warm, shallow seas that covered southern Britain millions of years ago.
The photograph shows the actual fossil specimen you will receive, allowing you to examine its natural shape, ribbing, colouration, preservation and any remaining geological matrix before purchasing. Every authentic fossil has its own combination of shell detail, mineralisation and surface character, making this an individual collectable specimen rather than a representative example.
Full sizing please see photo.
Bajocian Middle Jurassic Geology
The Bajocian Stage forms part of the Middle Jurassic and dates from approximately 170 to 168 million years ago. During this interval, southern England was covered by a broad marine shelf connected to extensive seas across north-western Europe.
These ancient waters supported a diverse ecosystem containing ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids and numerous other marine organisms. Carbonate mud, shell debris, sand and clay accumulated across the seabed under changing conditions of water depth, current strength and sediment supply.
Periods of slow sedimentation could leave shells exposed on the sea floor before final burial. Currents sometimes moved, reoriented or concentrated fossil remains into particular horizons. These processes contributed to the fossil-rich Jurassic deposits for which Dorset is internationally recognised.
Ammonites are especially important to geological research because they evolved relatively quickly and were widely distributed. Differences in shell form and ornamentation allow geologists to identify successive ammonite assemblages and correlate Jurassic rock layers between separate localities.
Darellia recticostata Shell Characteristics
Darellia recticostata possessed a planispirally coiled shell, meaning that its whorls developed around a central umbilicus within a single plane. Each new whorl increased in size as the animal grew, gradually forming the familiar spiral shape associated with ammonites.
The species name recticostata refers to the characteristically straight or comparatively direct ribs visible across the shell flanks. These ribs form an important part of the ammonite’s ornamentation and contribute to its distinctive appearance.
The shell is generally compressed rather than highly inflated, producing a relatively streamlined profile. Rib strength and spacing may change across successive growth stages, with inner whorls potentially displaying finer ornamentation and later whorls carrying more widely spaced ribs.
The outer edge of an ammonite shell is known as the venter. Its shape, together with the width of the umbilicus, whorl proportions and style of ribbing, provides important information when comparing and identifying ammonite fossils.
Visible characteristics vary according to the specimen’s growth stage and preservation. Natural weathering, mineral replacement, compression and partial concealment by matrix can all influence how much of the original shell detail remains visible.
Ammonite Biology and Chambered Shell
The living animal occupied the final and largest part of the shell, known as the body chamber. Its head, eyes, mouth and tentacle-bearing soft tissues extended from the shell opening when the animal was active.
Earlier sections of the shell were divided by curved internal walls called septa. These created a sequence of chambers collectively known as the phragmocone. A narrow tube called the siphuncle connected the chambers and allowed the ammonite to regulate their liquid and gas content, assisting with buoyancy control.
Where the septa joined the shell wall, they produced patterned suture lines. These may become visible when the outer shell layer is naturally removed, weathered or carefully prepared.
Ammonites belonged to the Cephalopoda, the same broad group of marine molluscs that contains modern squid, cuttlefish, octopuses and nautiluses. They were highly successful throughout the Mesozoic Era and developed a remarkable variety of shell forms before becoming extinct at the end of the Cretaceous Period.
Sherborne Dorset Fossil Locality
Sherborne lies within a geologically important area of north-west Dorset, where Jurassic sedimentary rocks preserve evidence of prehistoric marine environments. Although Dorset is especially famous for its coastal fossil exposures, its inland quarries, road cuttings and former workings have also produced scientifically and historically significant fossils.
During the Middle Jurassic, the Sherborne region formed part of a marine depositional area influenced by changing sea levels, currents and sedimentation. Fossil-bearing limestones and associated sediments preserve remains from the ecosystems that occupied these ancient waters.
A documented Sherborne fossil has strong locality interest for collectors of British ammonites, Dorset fossils, Bajocian fossils and Middle Jurassic palaeontology. The recorded provenance gives the specimen additional geological context and connects it directly with one of Britain’s best-known fossil-producing counties.
Scientific and Geological Details
Fossil type: Ammonite
Scientific name: Darellia recticostata
Order: Ammonitida
Geological period: Jurassic
Geological epoch: Middle Jurassic
Geological stage: Bajocian
Locality: Sherborne, Dorset, United Kingdom
Ammonite classification is based on characteristics such as shell coiling, whorl section, umbilical width, ribbing, ventral structure and suture patterns. These details allow fossil specimens to be compared with scientifically described genera and species.
Natural Fossilisation and Preservation
After the ammonite died, its shell settled onto the Jurassic seabed or was moved by currents before burial. Sediment accumulated around and within the shell, protecting portions of it from complete destruction.
As burial continued, geological pressure compacted the surrounding sediment. Mineral-rich groundwater altered or replaced parts of the original shell and eventually transformed the enclosing deposits into solid rock. The fossil may now preserve original or mineralised shell material, a natural internal mould, or a combination of both.
Any incomplete edges, attached matrix, minor fractures, worn ribbing, mineral-filled areas and natural colour variations are authentic geological characteristics. They record the specimen’s burial, fossilisation, exposure and recovery over millions of years.
Collectable British Jurassic Ammonite
This Darellia recticostata ammonite fossil would make an excellent addition to a collection of British fossils, Dorset ammonites, Sherborne fossils, Bajocian specimens or Middle Jurassic marine life. Its scientific identification and recorded locality also make it suitable for an educational collection, natural history display, fossil cabinet, 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.
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