Description
Genuine Garantiana (Pseudogarantiana) minima Ammonite Fossil
This carefully selected specimen is a genuine Garantiana (Pseudogarantiana) minima ammonite fossil from the Inferior Oolite Group at Horn Park Quarry, near Beaminster in Dorset, England, UK. It originates 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 fossil is identified to species level as Garantiana minima, within the subgenus Pseudogarantiana. Its comparatively compact shell, strongly defined ornamentation and accurately recorded geological provenance make it an appealing specimen for collectors of British ammonites, Dorset fossils and scientifically documented Jurassic material.
The photograph shows the actual fossil you will receive, rather than a stock image or representative example. Its individual coiling, rib pattern, colour, limestone matrix and natural preservation can therefore be examined before purchase. Full sizing is shown in the accompanying photograph.
Fossil Classification and Geological Information
Scientific name: Garantiana (Pseudogarantiana) minima
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Stephanoceratoidea
Family: Stephanoceratidae
Subfamily: Garantianinae
Genus: Garantiana
Subgenus: Pseudogarantiana
Species: 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. Changes in their shell shape, ribbing and coiling are useful for distinguishing successive fossil-bearing horizons within the Bajocian marine succession.
Compact Pseudogarantiana Shell Morphology
The shell grew in a flat spiral known as planispiral coiling. Each new whorl increased in size as the animal matured, creating the familiar circular form associated with ammonites. The central exposed region is called the umbilicus, the sides of the shell are known as the flanks, and the outermost edge is called the venter.
Garantiana ammonites commonly possess evolute or moderately evolute shells. In this style of coiling, successive whorls overlap relatively little, leaving much of the earlier spiral visible around a clearly defined central umbilicus. The compact proportions associated with Pseudogarantiana minima allow the detailed ornamentation of the inner whorls to remain an important feature of the fossil.
Strong primary ribs typically begin near the umbilical margin and extend across the flanks. These commonly divide into two finer secondary ribs towards the outer portion of the whorl, a branching pattern known as bifurcation. Additional secondary ribs may occasionally occur between the principal rib bundles.
The ribs can be straight, gently curved or slightly inclined forwards as they approach the ventral region. Their spacing and strength may change throughout growth, meaning that the juvenile inner whorls can show subtly different ornamentation from the larger outer whorl.
A shallow ventral interruption or groove may separate ribs arriving from opposite sides of the shell. This combination of open coiling, pronounced 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 the shell, known as the body chamber. The older inner section was divided into a series of sealed compartments by curved walls called septa.
A slender tube known as the siphuncle connected these chambers near the shell’s outer margin. By regulating the balance of liquid and gas within them, the ammonite could control its buoyancy and maintain an effective position in the water column.
Where each septum met the outer shell wall, it produced a complex suture line. These patterns consist of intricately divided lobes and saddles and may become visible where the original shell surface has weathered away or has been exposed through fossil preparation.
The animal itself was a soft-bodied marine mollusc related to other cephalopods. It probably possessed well-developed eyes, grasping appendages and a muscular funnel used to expel water for jet-propelled movement. Its chambered external shell provided physical protection while 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. It records an interval during which extensive shallow seas covered substantial areas of western Europe and ammonites evolved into numerous distinctive forms.
This specimen comes from the Subfurcatum Zone, a recognised ammonite biozone within the Bajocian succession. Biozones are intervals of sedimentary rock defined by characteristic fossil assemblages and the appearance, development or disappearance of particular ammonite groups.
Ammonites are highly valuable as index fossils because they evolved rapidly, were abundant and occupied geographically widespread marine environments. Their successive species allow geologists to compare individual limestone beds between quarries, coastal exposures and separate regions.
The recorded Subfurcatum Zone provenance gives this fossil important stratigraphic context. It links the specimen to a defined interval of Middle Jurassic time rather than identifying it only as a broadly dated Jurassic ammonite.
Inferior Oolite Group Geology
The Inferior Oolite Group is a varied succession of Middle Jurassic marine sedimentary rocks extending through parts of southern and central England. In Dorset, it contains numerous limestone beds formed from carbonate mud, ooids, peloids, shell fragments, sand grains and iron-bearing minerals.
Ooids are small, rounded carbonate grains formed when calcium carbonate accumulated in concentric layers around tiny particles within warm, agitated seawater. Although these grains contributed to the name “Inferior Oolite”, the group includes many different limestone types, and not every individual bed is strongly oolitic.
The succession records repeated changes in sea depth, current strength, sediment supply and seabed stability. Some horizons accumulated extremely slowly and became condensed, resulting in concentrations of shells, worn fossil fragments and mineral-coated surfaces. Other beds represent more continuous periods of carbonate deposition.
Ammonites preserved within these limestones are especially significant because their rapid evolutionary changes provide the detailed biostratigraphic framework used to determine the sequence and relative ages of individual beds.
Horn Park Quarry, Beaminster
Horn Park Quarry is a nationally and internationally important geological locality near Beaminster in west Dorset. Its preserved quarry faces expose a highly detailed Inferior Oolite succession containing fossil-rich horizons that have been studied extensively by generations of geologists and palaeontologists.
Historic limestone extraction revealed a condensed series of Middle Jurassic beds containing diverse ammonite assemblages. These fossils have played an important role in reconstructing Bajocian cephalopod evolution and refining the stratigraphic correlation of the British Inferior Oolite Group.
The locality is now protected for its geological significance. Fossils with accurately recorded Horn Park Quarry provenance are therefore particularly desirable, as they retain a direct connection to one of Britain’s most important 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 currents, scavengers and chemical dissolution.
As further sediment accumulated, the surrounding material became compacted and cemented into limestone. Mineral-rich groundwater could fill the shell chambers, replace original shell material or form an internal mould preserving the ammonite’s shape. Later uplift, erosion and quarrying exposed the fossil-bearing rocks.
Actual Specimen and Certificate of Authenticity
This is a genuine fossil specimen and not a replica, cast or modern reproduction. It has been individually chosen for its natural character, geological interest and collectable appearance. Variations in colour, limestone matrix, mineralisation, completeness and surface texture are authentic results of burial, fossilisation and natural weathering.
The listing photograph shows the exact Garantiana (Pseudogarantiana) 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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