Description
Genuine Parkinsonia cf. pachypleura Ammonite Fossil
This carefully chosen fossil is a genuine Parkinsonia cf. pachypleura ammonite from Burstock in Dorset, UK. It originates from the Inferior Oolite Group and is recorded from the Zigzag Zone of the Middle Jurassic, representing an extinct marine cephalopod that lived in the warm seas covering southern Britain approximately 166 to 168 million years ago.
The abbreviation “cf.” means “compare with” and indicates that the specimen closely resembles Parkinsonia pachypleura in its preserved shell form and ornamentation. This is a standard palaeontological identification used when the visible characteristics strongly support comparison with a named species, but preservation does not permit an entirely definitive species-level assignment.
The photograph shows the actual fossil specimen you will receive, allowing its individual coiling, ribbing, preservation, colour, matrix and natural geological characteristics to be examined before purchase. Full sizing and proportions can be seen in the accompanying photograph.
This authentic fossil includes a generic Certificate of Authenticity card with a lifetime guarantee.
Fossil Classification and Geological Details
Scientific identification: Parkinsonia cf. pachypleura
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Perisphinctoidea
Family: Parkinsoniidae
Geological period: Jurassic
Epoch: Middle Jurassic
Biozone: Zigzag Zone
Rock unit: Inferior Oolite Group
Locality: Burstock, Dorset, UK
Parkinsonia is an important genus of Middle Jurassic ammonites recognised by its evolute coiling and strongly developed rib pattern. The genus was named in honour of James Parkinson, the English surgeon, geologist and author whose pioneering work included influential studies of fossils and the organic remains preserved in rocks.
Parkinsoniid ammonites are valuable to palaeontologists because changes in their shell morphology help identify and correlate individual intervals within the later Bajocian and earliest Bathonian succession.
Distinctive Parkinsonia Shell Morphology
Parkinsonia cf. pachypleura possessed a planispirally coiled shell in which the whorls developed within a single flat plane. The shell is generally evolute, meaning that successive outer whorls overlap the earlier growth only slightly. This leaves a broad central umbilicus and allows much of the juvenile coiling to remain visible.
The flanks bear strong primary ribs that arise near the umbilical margin and travel outwards across the shell. These commonly divide into two secondary ribs towards the outer flank. Shorter intercalated ribs may also occur between the longer primary ribs, creating the dense and regular ornamentation associated with Parkinsonia.
The outer edge of the shell is known as the venter. In many Parkinsonia ammonites, the ribs weaken or become interrupted across this area, producing a smooth or shallow ventral groove. This feature, together with the rib division, whorl proportions and broad umbilicus, assists palaeontologists in distinguishing the genus from related perisphinctoid ammonites.
The name pachypleura refers to comparatively thick or robust flanks. Specimens associated with this form may display substantial whorls and pronounced ornamentation, although the precise appearance varies according to growth stage and preservation.
Any fractures, incomplete sections, mineral staining, surface wear or attached matrix are natural features produced during fossilisation and later geological exposure.
Zigzag Zone Biostratigraphy
The Zigzag Zone is a recognised ammonite biozone near the transition between the Bajocian and Bathonian stages of the Middle Jurassic. It is named after Parkinsonia zigzag, one of the characteristic ammonites used to identify this interval.
A biozone is a body of sedimentary rock recognised through the presence of a particular fossil species or assemblage. Ammonites are exceptionally useful for this purpose because they evolved rapidly and were widely distributed throughout Jurassic marine environments.
Successive forms of Parkinsonia provide a detailed record of evolutionary change through this part of Middle Jurassic time. Their shell shape, ribbing and adult morphology allow fossil-bearing beds from Dorset to be compared with corresponding deposits elsewhere in Britain and continental Europe.
The Zigzag Zone attribution therefore gives this fossil a much more precise geological context than the general description of Middle Jurassic alone. It places the specimen within a significant interval marked by changing ammonite faunas and evolving marine environments.
Inferior Oolite Geology of Dorset
The Inferior Oolite Group is a complex succession of Middle Jurassic marine rocks exposed across Dorset, Somerset and neighbouring parts of southern England. Despite its name, the group contains more than oolitic limestone. Its deposits include limestone, marl, sandstone, shell-rich beds and locally iron-bearing sediment.
During the time represented by these rocks, southern Britain lay beneath a warm epicontinental sea connected to the wider marine basins of north-western Europe. Britain formed an archipelago of islands, shallow carbonate platforms and marine channels rather than the continuous landmass seen today.
Sediment accumulated across the seabed under changing conditions. Carbonate grains, broken shells, mud and sand were transported by currents and deposited in environments ranging from relatively shallow, energetic water to quieter offshore settings.
Some layers accumulated extremely slowly and became condensed. Such beds may contain fossils, mineral grains and sedimentary material representing an extended period of geological time within a relatively thin rock layer. Other deposits show evidence of erosion and reworking before final burial.
The marine ecosystem included ammonites, belemnites, nautiloids, bivalves, brachiopods, gastropods, echinoids and crinoids. Fish and marine reptiles occupied higher levels within the food web, while worms and other invertebrates lived on or beneath the seabed.
Middle Jurassic Geology of Burstock
Burstock lies near Broadwindsor in west Dorset, within an area well known for inland exposures of the Inferior Oolite Group. Fossil-bearing quarries, lanes and agricultural workings in this district have revealed ammonite horizons that may be poorly exposed or completely concealed elsewhere.
Accurately recorded fossils from Burstock are valuable because their stratigraphic positions can be connected with established ammonite zones. This allows comparison with other important Dorset localities and contributes to a more detailed understanding of Middle Jurassic sedimentation across southern England.
The rocks around Burstock preserve evidence of fluctuating sea levels, changing currents and variations in the rate at which sediment reached the seabed. Ammonites provide the principal framework for arranging these deposits into chronological order.
Life of a Parkinsonia Ammonite
Ammonites were extinct marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. The animal occupied the final and largest section of its shell, known as the body chamber. Its head, eyes and tentacle-bearing soft body extended through the aperture.
The older coiled portion of the shell was divided into a series of chambers by curved internal walls called septa. A narrow tube known as the siphuncle connected these chambers and enabled the animal to regulate their liquid and gas content. This system provided buoyancy control and helped the ammonite maintain its position in the water column.
Movement was achieved through jet propulsion. Water was drawn into the mantle cavity and expelled through a muscular funnel, pushing the animal in the opposite direction. Tentacles surrounding the mouth were probably used to capture small crustaceans, planktonic organisms and other marine prey.
As the ammonite grew, it added new calcium carbonate shell material around the aperture. The animal moved forwards into an enlarged body chamber and formed a new septum behind itself, gradually producing the chambered spiral preserved in the fossil record.
Natural Fossilisation and Authentic Preservation
After death, the ammonite shell settled onto the Middle Jurassic seabed. The soft tissues decayed while sediment entered and accumulated around the empty shell. Burial helped protect the remains from complete destruction by currents, scavengers and chemical dissolution.
Over millions of years, the surrounding sediment became compacted and cemented into rock. Mineral-rich groundwater could recrystallise, replace or dissolve the original aragonitic shell. Sediment filling the chambers hardened into an internal mould that retained the ammonite’s coiled form and impressions of its original ornamentation.
Natural fractures, matrix attachments, mineral deposits, weathered areas and incomplete sections form part of the specimen’s individual geological history. These features make every fossil unique and provide visible evidence of its natural origin and immense age.
The photograph shows the exact carefully selected Parkinsonia cf. pachypleura ammonite fossil you will receive. Full sizing is shown in the photo. A generic Certificate of Authenticity card with a lifetime guarantee is included.
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