Description
Genuine Garantiana garantiana Ammonite Fossil
This carefully chosen fossil is a genuine Garantiana garantiana ammonite from the Inferior Oolite Group at Bothenhampton Brickworks, Dorset, UK. It dates from the Middle Bajocian Stage of the Middle Jurassic and is recorded from the Garantiana Zone, an important ammonite biozone used to identify and correlate fossil-bearing marine rocks.
This specimen represents an extinct marine cephalopod that lived in the warm Jurassic seas covering southern Britain approximately 169 million years ago. The listing photograph shows the actual fossil specimen you will receive, allowing its natural preservation, shell features, matrix, colouration and individual geological character to be viewed before purchase.
Full sizing please see photo.
Middle Bajocian Garantiana Zone
The Garantiana Zone is a recognised ammonite biozone within the Middle Bajocian. It takes its name from the genus Garantiana, whose distinctive shells are useful for identifying strata of this age.
Ammonite zones are based on the occurrence of characteristic species within particular rock layers. Because ammonites evolved rapidly and were widely distributed through Jurassic seas, they are among the most important index fossils used in geological dating. The presence of Garantiana garantiana therefore provides valuable evidence for the age and stratigraphic position of the bed from which the specimen originated.
The Middle Bajocian formed part of a period of extensive marine deposition across western Europe. Southern Britain lay beneath a shallow sea populated by ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids and other marine organisms. Their remains accumulated within sediment and were gradually preserved in the fossil record.
Inferior Oolite Group Geology
The Inferior Oolite Group is one of the most fossil-rich Middle Jurassic rock successions in southern England. It contains a varied sequence of oolitic limestones, marls, sandy beds, iron-rich deposits and condensed fossil horizons.
Oolitic limestone forms from tiny rounded carbonate grains known as ooids. These developed as calcium carbonate accumulated around small shell fragments or sediment particles moving in warm, agitated seawater. The resulting deposits indicate shallow marine conditions influenced by currents, waves and changing water depths.
Periods of slow sedimentation, erosion and reworking sometimes concentrated shells and other remains on the seabed. These condensed horizons can contain rich ammonite assemblages representing several stages of marine colonisation and deposition. The varied geology of the Inferior Oolite Group makes it particularly important for understanding the changing environments and ammonite faunas of the Middle Jurassic.
Bothenhampton Brickworks is associated with the historically important fossil-bearing geology of west Dorset. Specimens recorded from this locality provide a direct connection to the region’s long history of quarrying, brickmaking and palaeontological collecting.
Garantiana Ammonite Morphology
Garantiana ammonites are known for their strongly ornamented, planispirally coiled shells. The shell developed in a single plane around a central umbilicus, with the inner whorls remaining visible to varying degrees.
The flanks typically carry prominent ribs that rise from the umbilical region and divide as they extend towards the outer edge of the shell. These secondary ribs cross the ventral area, producing a distinctive sculptured appearance. Some specimens may also display raised tubercles or nodes where the primary ribs divide.
The combination of whorl shape, ribbing style, rib density and ventral ornamentation helps specialists distinguish Garantiana from related Bajocian ammonites. Visible features can vary according to the animal’s growth stage and the extent to which the shell has been preserved, weathered or retained within the surrounding matrix.
Internally, the ammonite shell was divided by walls called septa into a series of chambers. The animal occupied the final body chamber, while the older chambers formed the phragmocone. Regulation of gas and liquid within these chambers helped control buoyancy in the water column.
Scientific Classification and Fossil Details
Fossil type: Ammonite
Scientific name: Garantiana garantiana
Family: Stephanoceratidae
Subfamily: Garantianinae
Superfamily: Stephanoceratoidea
Order: Ammonitida
Geological period: Jurassic
Geological epoch: Middle Jurassic
Geological stage: Middle Bajocian
Biozone: Garantiana Zone
Geological unit: Inferior Oolite Group
Locality: Bothenhampton Brickworks, Dorset, United Kingdom
The Stephanoceratidae were a diverse family of Middle Jurassic ammonites, many of which possessed robust shells with pronounced ribbing and tuberculation. Their rapid evolutionary changes make them valuable for detailed biostratigraphic studies of Bajocian rocks.
Natural Fossil Preservation
Following the ammonite’s death, its shell settled onto the Jurassic seabed and became buried within accumulating marine sediment. During fossilisation, the original shell material could be replaced, altered or dissolved, leaving preserved shell, a mineralised internal mould or a combination of both.
Any attached matrix, incomplete areas, natural fractures, worn ribs, mineral-filled chambers or variations in colour are authentic geological characteristics. These features reflect burial, compaction, mineralisation and later exposure of the fossil-bearing rock.
Each ammonite is therefore unique, with its own preservation pattern and surface details formed over millions of years.
Collectable Dorset Jurassic Specimen
This Garantiana garantiana ammonite fossil would make an excellent addition to a collection of British fossils, Dorset ammonites, Bajocian fossils, Inferior Oolite specimens or Jurassic marine life. Its documented species, locality and biozone also make it suitable for geological study, educational display, a natural history cabinet or a distinctive gift for a fossil collector.
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.
Reviews
There are no reviews yet.