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 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 scientific abbreviation “cf.” means “compare with” and indicates that the fossil displays characteristics closely comparable to Garantiana minima. The identification is presented with suitable palaeontological caution because not every feature required for an entirely certain species-level determination may be visible or preserved. This is standard scientific terminology and provides a precise description without overstating the identification.
The listing photograph shows the actual fossil you will receive rather than a stock image or representative specimen. 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 Information
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 and its associated subgeneric forms belong to a distinctive group of strongly ornamented Middle Jurassic ammonites. Their changing shell proportions, coiling and rib patterns are useful for recognising and correlating fossil-bearing horizons within the Bajocian succession.
Compact Pseudogarantiana Shell Morphology
The ammonite shell grew in a flat spiral known as planispiral coiling. Each new whorl increased in diameter as the animal matured, forming the recognisable coiled outline. The central exposed region is called the umbilicus, the sides of the shell are known as the flanks, and the outer margin is called the venter.
Members of the Garantiana group generally 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 umbilicus. The smaller and more compact proportions associated with Pseudogarantiana forms can create a particularly detailed fossil in which the juvenile inner whorls and their ornamentation remain prominent.
Primary ribs typically arise near the umbilical margin and extend outwards across the flanks. These may divide into two finer secondary ribs towards the outer portion of the whorl, a branching pattern known as bifurcation. Additional secondary ribs can sometimes occur between the main rib bundles.
Depending on growth stage and preservation, the ribs may be straight, gently curved or inclined forwards as they approach the venter. Rib strength, spacing and direction can also change during growth, meaning that the inner whorls may show a different pattern from the later outer section.
A shallow interruption or groove may occur along the ventral region, where the ribs approaching from opposite flanks become reduced or separated. This combination of open coiling, prominent radial ornament and ventral differentiation gives garantianid ammonites their distinctive appearance.
Chambered Shell and Ammonite Anatomy
The living ammonite occupied the final and largest part of its shell, known as the body chamber. The older inner portion was divided into numerous sealed compartments by curved walls called septa.
A narrow tube known as the siphuncle passed through the chambers near the outer side of the shell. By adjusting the balance of liquid and gas within them, the ammonite could regulate buoyancy and maintain an effective position within the water column.
Where the septa met the shell wall, they created intricate suture lines. These patterns are formed from branching lobes and saddles and may be visible where the original outer shell layer has weathered away or has been exposed during careful fossil preparation.
The animal itself was a soft-bodied marine mollusc related to other cephalopods. It likely possessed a head, developed eyes, grasping appendages and a muscular funnel used to expel water for jet-propelled movement. Its external chambered shell provided 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 represents a time when shallow marine environments extended across substantial areas of western Europe and ammonites evolved into many distinctive forms.
This fossil is recorded from the Subfurcatum Zone, a recognised ammonite biozone within the Bajocian succession. Biozones are intervals of sedimentary rock distinguished by characteristic fossil assemblages and the appearance, development or disappearance of particular ammonite groups.
Ammonites are especially valuable as index fossils because they evolved rapidly, were abundant and lived across geographically widespread seas. Their successive faunas allow geologists to compare individual beds between separate quarries, coastal exposures and regions.
The Subfurcatum Zone provenance gives this specimen important geological context. It links the fossil to a defined portion 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 found across parts of southern and central England. In Dorset, it contains multiple limestone beds formed from carbonate mud, ooids, peloids, shell fragments, sand grains and iron-bearing minerals.
Ooids are small, rounded carbonate grains produced when 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 activity and seabed stability. Some horizons accumulated slowly and became condensed, producing concentrations of shells and other fossil material. Other beds represent more sustained episodes of limestone formation.
Ammonites are among the most important fossils in these rocks because their evolutionary succession provides the biostratigraphic framework used to establish the relative ages and relationships 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 detailed section through the Inferior Oolite Group and have been studied extensively for their varied Middle Jurassic ammonite faunas.
Historic quarrying exposed a condensed succession of fossil-rich limestone horizons. The ammonites recovered from these beds have helped palaeontologists reconstruct Bajocian cephalopod evolution and refine the correlation of British Middle Jurassic strata.
The locality is now protected for its geological significance. Fossils with recorded Horn Park Quarry provenance are therefore particularly desirable because they retain a direct connection to one of Britain’s most important Jurassic reference sites.
Middle Jurassic Marine Environment
During the Bajocian, Dorset lay beneath a warm, relatively shallow sea. Carbonate mud, ooids, shell debris and other 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 inhabited the surrounding water column, while burrowing, grazing and encrusting organisms occupied the seabed.
After death, the ammonite shell could drift temporarily or sink directly to the seafloor. Burial beneath sediment helped protect it from complete destruction by currents, scavengers and chemical dissolution.
As more layers accumulated, the sediment was 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 shape. Later uplift, erosion and quarrying exposed the fossil-bearing beds.
Actual Specimen 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 and surface texture are authentic results of burial, fossilisation and natural 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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