Description
Genuine Garantiana (Pseudogarantiana) cf. minima Ammonite Fossil
This carefully chosen specimen is a genuine Garantiana (Pseudogarantiana) cf. minima ammonite fossil from the Inferior Oolite Group at Horn Park Quarry, near Beaminster in Dorset, England, UK. It comes from the Lower Bajocian Subfurcatum Zone and represents an extinct marine cephalopod that inhabited the warm, shallow seas covering southern Britain during the Middle Jurassic.
The scientific abbreviation “cf.” means “compare with”. It indicates that the fossil displays characteristics closely comparable to Garantiana minima, while the identification retains an appropriate degree of caution because every feature required for completely certain species-level attribution may not be visible or preserved. This is standard palaeontological terminology and provides an accurate identification without overstating the available evidence.
The listing photograph shows the actual fossil you will receive rather than a stock image or representative example. Its individual shell form, ribbing, colour, limestone matrix and natural preservation can therefore be examined before purchase. Full sizing is shown in the accompanying photograph.
Fossil Classification and Geological Details
Scientific identification: Garantiana (Pseudogarantiana) cf. minima
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Stephanoceratoidea
Family: Stephanoceratidae
Subfamily: Garantianinae
Genus: Garantiana
Subgenus: Pseudogarantiana
Comparable species: Garantiana minima
Geological period: Jurassic
Epoch: Middle Jurassic
Stage: Bajocian
Stratigraphic interval: Lower Bajocian
Ammonite biozone: Subfurcatum Zone
Rock unit: Inferior Oolite Group
Locality: Horn Park Quarry, Beaminster, Dorset, UK
Garantiana belongs to a distinctive group of strongly ornamented Middle Jurassic ammonites. Differences in shell proportions, coiling, rib density and ventral structure are useful for distinguishing related forms and correlating fossil-bearing horizons within the Bajocian succession.
Compact Pseudogarantiana Shell Morphology
The shell grew in a flat spiral known as planispiral coiling. Each new whorl increased in size as the ammonite matured, creating the recognisable circular form. The central exposed area is called the umbilicus, the lateral surfaces are known as the flanks, and the shell’s outer edge is called the venter.
Members of the Garantiana group generally possess evolute or moderately evolute shells. In this style of coiling, successive whorls overlap only slightly, leaving much of the earlier spiral exposed around a clearly defined umbilicus. The compact proportions associated with Pseudogarantiana minima allow the inner whorls and their detailed ornamentation to remain prominent.
Strong primary ribs typically begin close to the umbilical margin and extend across the flanks. These commonly divide into two finer secondary ribs towards the outer part of the whorl, a branching pattern known as bifurcation. Additional secondary or intercalated ribs may occur between the principal rib bundles.
The ribs can be straight, gently curved or inclined forwards as they approach the venter. Their strength, spacing and direction may change during growth, meaning that the juvenile inner whorls can display subtly different ornamentation from the mature outer section.
A shallow groove or interruption may occur along the ventral region, where ribs approaching from opposite flanks become reduced or separated. This combination of open coiling, prominent radial ribbing and ventral differentiation gives garantianid ammonites their characteristic textured appearance.
Chambered Shell and Ammonite Anatomy
The living ammonite occupied the final and largest portion of its shell, known as the body chamber. The older inner section was divided into numerous sealed compartments by curved internal walls called septa.
A slender tube known as the siphuncle passed through the chambered shell near its outer margin. By regulating the proportions of liquid and gas within these chambers, the ammonite could control buoyancy and maintain an effective position within the water column.
Where the septa joined the exterior shell wall, they produced complex suture lines. These consist of intricately divided lobes and saddles and may become visible where the original shell surface has weathered away or has been exposed during careful preparation.
The animal itself was a soft-bodied marine mollusc related to other cephalopods. It likely possessed developed eyes, grasping appendages and a muscular funnel through which water could be expelled for jet-propelled movement. Its external chambered shell provided protection while also functioning as a specialised buoyancy system.
Lower Bajocian Subfurcatum Zone
The Bajocian is the second stage of the Middle Jurassic, following the Aalenian and preceding the Bathonian. During this interval, warm marine environments extended across substantial areas of western Europe and ammonites diversified into numerous recognisable groups.
This specimen comes from the Subfurcatum Zone, an established ammonite biozone within the Bajocian succession. Biozones are intervals of sedimentary rock identified by characteristic fossil assemblages and the appearance, development or disappearance of particular ammonite forms.
Ammonites are exceptionally useful index fossils because they evolved rapidly, were abundant and occupied geographically widespread seas. Their successive faunas allow geologists to compare individual beds between quarries, coastal exposures and separate regions with considerable precision.
The recorded Subfurcatum Zone provenance gives this specimen important stratigraphic context. It links the ammonite to a defined interval of Middle Jurassic time rather than identifying it only as a broadly dated Jurassic fossil.
Inferior Oolite Group Geology
The Inferior Oolite Group is a varied succession of Middle Jurassic marine sedimentary rocks found across parts of southern and central England. In Dorset, it includes numerous limestone beds formed from carbonate mud, ooids, peloids, shell fragments, sand grains and iron-bearing minerals.
Ooids are small, rounded carbonate grains created as calcium carbonate accumulated in concentric layers around tiny particles in warm, moving seawater. Although these grains contributed to the name “Inferior Oolite”, the group contains many different limestone types, and not every bed is strongly oolitic.
The succession records repeated changes in water depth, sediment supply, current strength and seabed stability. Some horizons accumulated very slowly and became condensed, producing concentrations of worn shells, mineral-coated fossils and reworked biological material. Other beds represent more continuous periods of carbonate deposition.
Ammonites are among the most important fossils preserved within these rocks because their rapid evolutionary changes provide the detailed biostratigraphic framework used to determine the sequence and relative ages of individual limestone beds.
Horn Park Quarry, Beaminster
Horn Park Quarry is an important Middle Jurassic geological locality near Beaminster in west Dorset. Its preserved quarry faces expose a detailed section through the Inferior Oolite Group and have been studied extensively for their varied ammonite faunas.
Historic limestone extraction revealed a condensed succession of fossil-rich horizons. Ammonites recovered from these beds have contributed significantly to the study of Bajocian cephalopod evolution and the refinement of British Middle Jurassic stratigraphy.
The locality is protected for its geological importance. Fossils with accurately recorded Horn Park Quarry provenance are therefore particularly desirable because they retain a direct connection to one of Britain’s most significant Jurassic reference sites.
Middle Jurassic Marine Environment
During the Bajocian, the area now forming Dorset lay beneath a warm, relatively shallow sea. Carbonate mud, ooids, shell debris and other marine sediment accumulated across the seabed under changing current and water-depth conditions.
Ammonites shared these waters with belemnites, nautiloids, brachiopods, bivalves, gastropods, echinoids, crinoids, crustaceans and fish. Marine reptiles occupied the surrounding water column, while burrowing, grazing and encrusting organisms lived upon or within the seabed.
After death, the ammonite shell may have drifted temporarily before sinking or descended directly to the seafloor. Burial beneath sediment helped protect it from complete destruction by scavengers, currents and chemical dissolution.
As additional layers accumulated, the surrounding sediment became compacted and cemented into limestone. Mineral-rich groundwater could fill the shell chambers, replace original shell material or create an internal mould preserving the ammonite’s form. Later uplift, erosion and quarrying exposed the fossil-bearing rocks.
Actual Fossil and Certificate of Authenticity
This is a genuine fossil specimen and not a replica, cast or modern reproduction. It has been individually selected for its natural character, geological interest and collectable appearance. Variations in colour, limestone matrix, mineralisation, completeness, natural fractures and surface texture are authentic results of burial, fossilisation and weathering.
The listing photograph shows the exact Garantiana (Pseudogarantiana) cf. minima ammonite fossil that will be supplied. Full sizing is provided in the photograph so its dimensions can be assessed before purchase.
The specimen includes a generic Certificate of Authenticity card carrying a lifetime guarantee of authenticity. It is an excellent addition to a British ammonite collection, Middle Jurassic fossil display, Dorset geological collection, educational teaching set or natural-history cabinet.
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