Description
Genuine Dorsetensia politum Ammonite Fossil
This carefully selected specimen is a genuine Dorsetensia politum ammonite fossil from Horn Park near Beaminster, Dorset, England. It originates from the Beacon Limestone Formation and dates to the Aalenian Stage of the Middle Jurassic, representing an extinct marine cephalopod that lived approximately 170–174 million years ago.
The combination of an identified ammonite species, recognised geological formation and accurately recorded British locality makes this an appealing specimen for fossil collectors, ammonite enthusiasts, educational displays and natural-history collections. It offers a tangible connection to the warm Jurassic seas that once covered southern England.
The photographs show the exact fossil specimen you will receive. Full sizing and scale information can be seen in the accompanying photographs.
Beacon Limestone Formation Geology
The Beacon Limestone Formation is an important sequence of fossil-bearing marine rock exposed in parts of Dorset and Somerset. It was deposited during the Early to Middle Jurassic and includes limestone and marl horizons formed from carbonate-rich sediment accumulating on an ancient seabed.
During the Aalenian, the area now occupied by Dorset lay beneath a shallow marine environment. Fine sediment, broken shell material and calcium carbonate gradually collected across the sea floor. These deposits were later compacted and cemented into limestone, preserving the remains of ammonites and other marine organisms.
The Jurassic sea supported a diverse ecosystem that included ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids and numerous smaller invertebrates. When an ammonite died, its shell could sink to the seabed and become partially or completely buried. Over millions of years, the original shell material might be replaced, dissolved or filled with minerals, producing the fossilised shell, internal mould or impression seen today.
Natural differences in preservation, colour, surface texture and matrix are part of the specimen’s geological history. Any visible weathering, mineral staining, incomplete areas or fine fractures reflect the processes of burial, fossilisation and later exposure.
Dorsetensia politum Ammonite Characteristics
Dorsetensia is a genus of Jurassic ammonites recognised from Aalenian marine deposits. Its shells are generally coiled in a planispiral form, with successive whorls developing around a central umbilical area. Species identification is based on a combination of features that can include whorl shape, shell compression, umbilical proportions, ribbing and the form of the outer or ventral margin.
The ornamentation of Dorsetensia ammonites may include fine to moderately developed ribs extending across the shell flanks. These ribs can change in strength and spacing as the animal grows, creating a distinctive pattern across the preserved whorls. Depending on the condition of the specimen, visible features may include portions of the coiling, ribbed flanks, umbilical region, outer whorl, internal chambers or surrounding limestone matrix.
Every ammonite fossil is unique. Its final appearance records both the biological growth of the original animal and the geological events that affected the shell after death.
An Extinct Jurassic Marine Cephalopod
Ammonites were marine molluscs related to living squid, cuttlefish, octopuses and nautiluses. They possessed a coiled external shell divided internally into a series of chambers. The soft-bodied animal occupied the final and largest chamber, while the older chambers formed a buoyancy structure known as the phragmocone.
The chambers were connected by a narrow tube called the siphuncle. By regulating the balance of liquid and gas within the shell, the ammonite could control its buoyancy and move through the water column. This adaptation helped ammonites become one of the most successful and diverse marine groups of the Mesozoic Era.
As an ammonite grew, it constructed progressively larger chambers around the outside of its shell. The internal partitions met the shell wall along intricate lines called sutures. Shell shape, ribbing, whorl proportions and suture patterns are all useful features in ammonite classification.
Horn Park Fossil Locality in Dorset
Horn Park, near Beaminster, is a highly regarded Jurassic fossil locality associated with the Inferior Oolite succession of Dorset. The exposed rocks preserve an important record of marine life and environmental change during the Aalenian and Bajocian stages.
Ammonites from these beds are especially valuable because they evolved rapidly and can help geologists identify and correlate individual layers of rock. A specimen with recorded formation, stage and locality therefore has greater scientific and collectable value than an ammonite lacking geological information.
This Dorsetensia politum fossil would make a distinctive addition to a British fossil collection, Jurassic display, study cabinet or educational collection.
Actual Specimen with Certificate of Authenticity
This is a genuine fossil specimen and not a cast, replica or reproduction. It has been carefully chosen for its natural form, geological interest and individual character.
The photographs show the actual Dorsetensia politum ammonite fossil you will receive. Full sizing is shown in the photographs.
A generic Certificate of Authenticity card is included with a lifetime guarantee of authenticity, providing lasting confidence that this is a genuine Middle Jurassic fossil specimen.
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