Description
Genuine Ludwigia crassa Ammonite Fossil
This carefully selected specimen is a genuine Ludwigia crassa ammonite fossil from Burton Bradstock in Dorset, UK. It dates from the Upper Aalenian Stage of the Middle Jurassic and represents an extinct marine cephalopod that inhabited the seas covering southern Britain approximately 171 million years ago.
Ludwigia crassa is a scientifically significant graphoceratid ammonite associated with the Murchisonae Zone of the Aalenian. Its robust shell proportions, distinctive ribbing and important position within the Middle Jurassic ammonite succession make it an appealing specimen for collectors of British fossils, Dorset palaeontology and classic Jurassic ammonites.
The photograph shows the actual fossil you will receive, allowing its individual coiling, ornamentation, preservation, colour, matrix and natural geological features to be examined before purchase. Full sizing and proportions can be seen in the accompanying photograph.
This fossil is supplied with a generic Certificate of Authenticity card carrying a lifetime guarantee.
Fossil Classification and Geological Information
Scientific name: Ludwigia crassa
Fossil type: Ammonite
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Hammatoceratoidea
Family: Graphoceratidae
Geological period: Jurassic
Epoch: Middle Jurassic
Stage: Upper Aalenian
Biozone: Murchisonae Zone
Subzone: Haugi Subzone
Locality: Burton Bradstock, Dorset, UK
The species was described by the German palaeontologist Max Horn in 1909 and has also been treated as Ludwigia murchisonae crassa. The genus Ludwigia belongs to the Graphoceratidae, an important family of keeled and strongly ornamented ammonites that underwent rapid evolutionary change during the Aalenian.
Because graphoceratid shell forms changed through relatively short intervals of geological time, they are highly valuable for identifying and correlating Middle Jurassic sedimentary rocks.
Robust Shell Form and Ribbed Ornamentation
The specific name crassa refers to the comparatively stout or robust proportions of this ammonite. Its shell is planispirally coiled, with each whorl developing around a central umbilicus in a single flat plane.
The whorls are typically compressed to moderately inflated, with broad flanks and a defined outer margin. Primary ribs begin near the umbilical shoulder and extend across the sides of the shell. These ribs may curve forwards, strengthen towards the outer flank or divide as they approach the venter.
The venter is the outermost edge of the ammonite shell. In Ludwigia, it commonly bears a prominent keel, creating a sharp ridge around the shell’s circumference. This combination of curved ribbing, compressed coiling and a keeled venter gives the genus its characteristic streamlined appearance.
The ornamentation may change as the animal grows. Inner whorls can display finer, more closely spaced ribs, while later growth may become coarser or more widely spaced. Such variations record different stages in the ammonite’s development.
Any natural fractures, incomplete sections, worn areas, mineral deposits or attached matrix are genuine characteristics resulting from fossilisation and subsequent geological exposure.
Upper Aalenian Murchisonae Zone
The Aalenian is the earliest stage of the Middle Jurassic, following the Toarcian and preceding the Bajocian. Ludwigia crassa is associated with the Murchisonae Zone and particularly the Haugi Subzone within the Upper Aalenian.
The Murchisonae Zone is named after Ludwigia murchisonae, one of the best-known index ammonites from this interval. It represents an important phase in the evolutionary history of the Graphoceratidae, during which numerous closely related shell forms appeared in the seas of Europe.
An ammonite biozone is a body of sedimentary rock recognised through the presence of a characteristic species or fossil assemblage. Rapid ammonite evolution allows palaeontologists to divide Jurassic rocks into narrow time intervals and compare deposits exposed in different regions.
The association of Ludwigia crassa with this established biostratigraphic framework provides the specimen with a more precise geological context than the broader description of Middle Jurassic alone.
Jurassic Geology of Burton Bradstock
Burton Bradstock is located on the Dorset coast and is renowned for its exposed Jurassic sedimentary succession. The cliffs include the Bridport Sand Formation, which is overlain by the fossil-bearing Inferior Oolite Group and younger Middle Jurassic deposits.
During the Aalenian, southern Britain formed part of an archipelago surrounded by shallow and moderately deep marine basins. Sediments accumulated on the seabed as sand, carbonate mud, shell debris, limestone and iron-rich material.
The Inferior Oolite succession records repeated changes in sea level, sediment supply, current activity and marine conditions. Some beds accumulated slowly and became condensed, concentrating fossils and mineral grains within relatively thin horizons.
Ammonites occurred alongside belemnites, bivalves, brachiopods, gastropods, echinoids and other marine invertebrates. Fish and marine reptiles occupied higher levels within the ecosystem, while burrowing organisms lived within the sediment below.
The fossil-bearing rocks around Burton Bradstock form part of the internationally celebrated Jurassic geology of Dorset. Their ammonite assemblages have contributed significantly to the detailed study of the Aalenian and Bajocian stages in southern England.
Life of a Middle Jurassic Ammonite
Ammonites were marine molluscs related to modern squid, cuttlefish, octopuses and nautiluses. The living animal occupied the final and largest portion of its shell, known as the body chamber.
The older coiled section was divided into smaller chambers by curved internal walls called septa. A narrow tube known as the siphuncle passed through these chambers and enabled the ammonite to regulate their liquid and gas content. This system provided buoyancy control and helped the animal maintain its position within 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. The compressed, keeled shell of Ludwigia crassa would have provided a relatively streamlined profile in the water.
Tentacles surrounding the mouth were probably used to capture small prey, collect food and investigate the environment. As the ammonite matured, new shell material was added around the aperture and additional chambers formed behind the living animal.
Natural Fossilisation and Preservation
After death, the ammonite shell settled onto the Aalenian seabed. Its soft tissues decayed while sediment accumulated around and within the empty shell. Burial helped protect the remains from currents, scavengers and complete physical destruction.
Over millions of years, the surrounding sediment was compacted and cemented into rock. Mineral-rich groundwater could dissolve, recrystallise or replace the original aragonitic shell. Sediment filling the chambers hardened into an internal mould that retained the coiled form and impressions of the original ribbing.
Each fossil has undergone its own history of burial, mineral alteration, geological movement, erosion and exposure. Differences in colour, surface texture, completeness and matrix are natural features that make every specimen individually distinctive.
The photograph shows the exact carefully chosen Ludwigia crassa ammonite 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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