Description
Genuine British Jurassic Ammonite Fossil
This genuine British ammonite fossil is identified as Lokuticeras cf. tenuicostatum and comes from Bank’s Quarry at Oborne in North Dorset, United Kingdom. It was preserved within the fossiliferous rocks of the Inferior Oolite Group and is assigned to the Humphriesianum Zone of the Lower Bajocian, Middle Jurassic.
The abbreviation “cf.” is derived from the Latin word confer, meaning “compare with.” In palaeontology, it indicates that the specimen closely resembles the named species, Lokuticeras tenuicostatum, although the available preserved characteristics do not allow an entirely definitive species-level determination. This careful terminology is commonly used for scientifically catalogued fossils where preservation, incomplete growth stages or natural variation affect identification.
The listing photographs show the actual fossil specimen you will receive. It has been individually selected for its recognisable ammonite form, geological interest and documented Dorset provenance.
Lokuticeras Ammonite Identification
Lokuticeras is a distinctive Bajocian ammonite associated with the stephanoceratid group of extinct marine cephalopods. Its broader scientific classification places it within the phylum Mollusca, class Cephalopoda and order Ammonitida. It is generally associated with the family Stephanoceratidae and superfamily Stephanoceratoidea, an important ammonite lineage that diversified extensively during the Bajocian Stage.
Ammonites related to Lokuticeras typically possess evolute or relatively openly coiled shells, leaving a broad central umbilicus and exposing much of the earlier whorls. Their ornament commonly consists of strong primary ribs rising from the inner portion of each whorl. These ribs may divide into finer secondary ribs across the flanks before continuing over the outer edge, or venter, of the shell.
The name tenuicostatum refers to comparatively slender or fine ribbing, an important feature used when comparing specimens with this species. The exact expression of the ribs can vary according to the ammonite’s growth stage, preservation and whether the fossil represents the original shell exterior or an internal mould of the chambers.
Humphriesianum Zone and Lower Bajocian Age
This specimen is recorded from the Humphriesianum Zone, one of the principal ammonite biozones used to subdivide the Lower Bajocian succession. Biozones are intervals of sedimentary rock recognised by their characteristic fossil assemblages, particularly rapidly evolving and widely distributed ammonites.
The Humphriesianum Zone takes its name from the well-known Bajocian ammonite Stephanoceras humphriesianum. Ammonite faunas from this interval are especially useful for comparing and correlating Middle Jurassic marine strata across Britain and continental Europe.
The Lower Bajocian dates from approximately 170 million years ago, when extensive shallow seas covered large areas of what is now southern England. The presence of a detailed zonal provenance gives this fossil considerably more scientific context than an ammonite offered only as a general Jurassic specimen.
Inferior Oolite Group Geology
The Inferior Oolite Group is an important sequence of Middle Jurassic sedimentary rocks found across parts of southern and central England. The word “Inferior” is a traditional stratigraphic term indicating that these rocks occur beneath the younger Great Oolite Group. It does not refer to the quality, condition or importance of the fossils.
The sequence is dominated by limestone and includes oolitic, bioclastic, sandy, marly and locally iron-rich deposits. Oolitic limestone contains numerous small, rounded calcium-carbonate grains called ooids. These developed as mineral layers accumulated around tiny particles moving in warm, shallow and agitated seawater.
Around Oborne, parts of the Inferior Oolite succession contain ferruginous or iron-rich material, which can give fossils and their surrounding matrix natural shades of brown, ochre, orange or reddish brown. Differences in colour, texture and mineral composition are genuine features produced during sedimentation, burial and fossilisation.
The fossiliferous beds preserve evidence of a diverse marine ecosystem that included ammonites, belemnites, brachiopods, bivalves, gastropods, echinoids and other invertebrates.
Life and Fossilisation of the Ammonite
Ammonites were extinct marine cephalopods related to living squid, cuttlefish, octopuses and nautiluses. The living animal occupied the final chamber of its coiled shell, while the earlier portion was divided by internal walls called septa.
These chambers were connected by a narrow tube known as the siphuncle. By regulating fluids and gases within the chambered shell, the ammonite could control its buoyancy and position in the water. The complex lines formed where the septa met the shell wall are known as sutures and are important features in ammonite classification.
After this ammonite died, its shell settled onto the Jurassic seabed. Burial beneath carbonate-rich sediment protected it from complete destruction. During fossilisation, the original shell material could be altered, dissolved or replaced by minerals, while sediment filling the shell preserved an internal mould of its shape and ornamentation.
Any natural fractures, areas of matrix, incomplete sections, surface weathering or variations in rib preservation form part of the specimen’s authentic geological history.
Bank’s Quarry, Oborne, North Dorset
Bank’s Quarry at Oborne lies within the historically important Inferior Oolite district surrounding Sherborne in North Dorset. The area is well known for its fossiliferous Bajocian strata and the detailed ammonite successions preserved within them.
During the Middle Jurassic, Oborne was situated beneath a warm marine environment where carbonate sediment accumulated across the seabed. Changing water depth, sediment supply, currents and biological activity produced a varied succession of limestone, marl and iron-rich deposits.
Ammonites from accurately recorded localities such as Bank’s Quarry are particularly desirable because their location and stratigraphic information allow them to be placed within a specific geological setting. The combination of quarry provenance, Inferior Oolite geology and Humphriesianum Zone dating makes this a scientifically interesting example of a Dorset Jurassic ammonite.
Actual Specimen and Certificate of Authenticity
This is a genuine fossil and not a cast, replica or artificial reproduction. The photographs show the exact Lokuticeras cf. tenuicostatum ammonite that will be supplied, allowing its preservation, natural colour, matrix and individual characteristics to be viewed before purchase.
Full sizing and scale information are provided in the listing photographs.
The fossil includes a generic Certificate of Authenticity card carrying a lifetime guarantee. Carefully chosen for its identifiable ammonite morphology and detailed geological provenance, this specimen is suitable for a British fossil collection, natural-history cabinet, educational display or specialist collection of Bajocian ammonites and Inferior Oolite fossils.
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