Description
Genuine Praeparkinsonia garantiformis Ammonite Fossil
This carefully chosen fossil is a genuine Praeparkinsonia garantiformis ammonite from the Inferior Oolite Group at Burton Bradstock, Dorset, UK. It dates from the Upper 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.
The specimen represents an extinct marine cephalopod that inhabited the warm Jurassic seas covering southern Britain approximately 168 million years ago. The listing photograph shows the actual fossil specimen you will receive, allowing its natural shell form, ribbing, preservation, colouration and attached matrix to be examined before purchase.
Full sizing please see photo.
Upper Bajocian Garantiana Zone
The Garantiana Zone is a recognised biostratigraphic division within the later Bajocian succession. It is defined using characteristic ammonite assemblages and takes its name from the genus Garantiana, one of the best-known ammonite groups associated with this interval.
Ammonites evolved comparatively rapidly and were widely distributed through Jurassic seas. Changes in shell shape, coiling, ribbing and ventral structure allow palaeontologists to distinguish successive faunas and divide the geological record into detailed zones and subzones. A specimen recorded from the Garantiana Zone therefore carries valuable geological information in addition to its appeal as a natural collectable.
During the Upper Bajocian, southern Britain formed part of a broad marine shelf connected to the north-west European sea. These waters supported a varied ecosystem containing ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids and other marine organisms.
Praeparkinsonia Shell Form and Ornamentation
Praeparkinsonia is a distinctive genus of Bajocian ammonite known for its evolute coiling and strongly developed ribbing. An evolute shell has a relatively open central umbilicus, leaving much of the earlier whorls visible rather than covering them with later growth.
The shell is planispirally coiled, with each whorl expanding around the previous one in a single plane. Primary ribs typically rise from the umbilical region and extend across the flanks. These may divide into secondary ribs as they approach the outer portion of the shell, producing a regular and strongly sculptured appearance.
The outer edge of the shell, known as the venter, may show a defined median groove or interruption in the ribbing, depending on growth stage and preservation. This ventral character, combined with whorl proportions and rib style, is important when comparing Praeparkinsonia with related Bajocian ammonites.
The species name garantiformis reflects its resemblance to ammonites associated with Garantiana. Its combination of open coiling, pronounced ribbing and stratigraphic occurrence makes it an interesting example of the changing ammonite faunas near the later part of the Bajocian.
Visible details can vary according to the age of the animal when it died, the amount of shell preserved and the effects of fossilisation. Inner whorls may carry finer and more closely spaced ornamentation, while later growth stages can develop broader rib spacing and more substantial whorl proportions.
Inferior Oolite Group Geology
The Inferior Oolite Group is one of southern England’s most important Middle Jurassic rock successions. It includes oolitic limestones, sandy limestones, marls, iron-rich beds and condensed fossil horizons deposited under changing shallow-marine conditions.
Oolitic limestone contains small rounded carbonate grains called ooids. These formed when calcium carbonate accumulated in layers around tiny sediment particles or shell fragments moving in warm, agitated seawater. The grains eventually settled, became compacted and were cemented together into limestone.
Deposition was frequently interrupted by sea-level changes, erosion and periods of slow sediment accumulation. Shells could remain exposed on the seabed, become transported by currents and collect within concentrated fossil horizons. These conditions contributed to the diverse and scientifically important ammonite assemblages preserved throughout the Inferior Oolite succession.
Burton Bradstock Jurassic Fossil Locality
Burton Bradstock lies on the famous Jurassic Coast of west Dorset, a region internationally recognised for its exceptional record of Mesozoic geology and prehistoric marine life. The cliffs and nearby inland exposures preserve sedimentary rocks deposited during several intervals of the Jurassic Period.
The Inferior Oolite deposits associated with Burton Bradstock record a dynamic shallow sea affected by changing currents, sediment supply and water depth. Fossils recovered from these rocks provide evidence of the marine communities inhabiting Dorset during the Middle Jurassic.
Ammonites from Burton Bradstock are highly collectable because they combine distinctive natural ornamentation with a documented British locality and detailed geological context. Each specimen provides a direct connection to the ancient sea and to Dorset’s long-established tradition of fossil discovery and study.
Scientific Classification and Fossil Details
Fossil type: Ammonite
Scientific name: Praeparkinsonia garantiformis
Family: Parkinsoniidae
Superfamily: Stephanoceratoidea
Order: Ammonitida
Geological period: Jurassic
Geological epoch: Middle Jurassic
Geological stage: Upper Bajocian
Biozone: Garantiana Zone
Geological unit: Inferior Oolite Group
Locality: Burton Bradstock, Dorset, United Kingdom
Parkinsoniid ammonites are recognised for their evolute shells, prominent ribbing and characteristic ventral features. They became particularly important during the later Bajocian and Bathonian and are useful fossils for studying changes within Middle Jurassic marine faunas.
Chambered Shell and Ammonite Biology
The living ammonite occupied the final and largest part of the shell, known as the body chamber. Earlier portions were divided by curved internal walls called septa, producing a series of chambers collectively known as the phragmocone.
These chambers contained regulated proportions of gas and liquid, helping the animal control buoyancy within the water column. The intersections between the septa and outer shell formed complex suture lines, which may become visible where the shell surface has been naturally removed or weathered.
Ammonites belonged to the cephalopods and were related to modern squid, cuttlefish, octopuses and nautiluses. They were highly successful marine animals throughout much of the Mesozoic Era and developed an extraordinary variety of shell forms before becoming extinct at the end of the Cretaceous Period.
Natural Fossil Preservation
After the ammonite died, its shell settled onto the Jurassic seabed or was moved by currents before burial. Sediment gradually accumulated around the remains, while compaction and mineral-rich groundwater transformed the surrounding deposits into rock.
The original shell material may have been preserved, replaced by minerals or dissolved to leave an internal mould. Many specimens retain a combination of mineralised shell, sediment-filled chambers and natural rock matrix.
Any incomplete areas, attached matrix, worn ribbing, mineral deposits, small fractures or variations in colour are genuine geological characteristics. These features reflect burial, fossilisation, erosion and eventual recovery from the host rock, giving every authentic ammonite its own unique appearance.
Collectable Dorset Ammonite Specimen
This Praeparkinsonia garantiformis ammonite fossil would make an excellent addition to a collection of British fossils, Dorset ammonites, Upper Bajocian fossils, Garantiana Zone specimens or Inferior Oolite fossils. Its documented identification, locality and geological horizon make it suitable for a fossil cabinet, natural history display, educational collection or distinctive gift for a Jurassic fossil enthusiast.
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.
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