Description
Genuine Tmetoceras scissum Ammonite Fossil
This carefully chosen specimen is a genuine Tmetoceras scissum ammonite fossil from the Scissum Bed at Burton Bradstock, Dorset, UK. It comes from the fossiliferous marine succession associated with the Inferior Oolite Formation and dates from the Aalenian Stage of the Middle Jurassic Period.
The Scissum Bed is an early Aalenian deposit rather than a Bajocian bed and is associated with the Opalinum Zone and Scissum biohorizon or zonal interval. Higher parts of the Inferior Oolite succession at Burton Bradstock extend into the Bajocian, but the Tmetoceras-bearing Scissum Bed belongs to the older Aalenian portion of the sequence.
Its recognised species, accurately recorded bed and classic Jurassic Coast provenance make this fossil especially appealing for collectors of British ammonites, Dorset fossils and stratigraphically documented Middle Jurassic specimens.
Tmetoceras scissum Shell Morphology
Tmetoceras scissum was a small, distinctively ornamented ammonite with a planispirally coiled and internally chambered shell. The species typically displays an evolute shell form, meaning that successive whorls overlap only slightly and leave a relatively broad central umbilicus. This open coiling allows several of the earlier whorls to remain visible.
The shell flanks commonly carry strong, relatively simple radial ribs. These ribs extend from the umbilical region towards the outer edge of the shell and give the ammonite its characteristic sculptured appearance. The outer margin, known as the venter, is generally narrow and may show a groove or interruption in the ribbing. Whorl proportions, rib strength, umbilical width and ventral form are among the features used when identifying Tmetoceras specimens.
The precise features visible on this individual fossil depend on its growth stage, preservation and the amount exposed from the surrounding matrix. Natural shell loss, mineral deposits, worn ribbing, incomplete whorls and areas of attached Jurassic rock are authentic results of burial, fossilisation and later weathering.
The species is conventionally cited as Tmetoceras scissum (Benecke, 1865), reflecting its original formal description by Ernst Wilhelm Benecke. The taxon is recognised as an accepted fossil ammonite species.
Ammonite Classification and Biology
Tmetoceras belongs to the extinct cephalopod order Ammonitida. Modern taxonomic arrangements place the genus within the superfamily Hildoceratoidea, family Graphoceratidae and subfamily Tmetoceratinae.
Ammonites were marine molluscs related more broadly to living squid, cuttlefish, octopuses and nautiluses. Their shells were divided internally into a series of chambers separated by curved walls called septa. The animal occupied the final and largest section, known as the body chamber, while the older chambered portion formed the phragmocone.
A narrow tube called the siphuncle connected the chambers. By controlling the balance of liquid and gas within them, the ammonite could regulate its buoyancy and maintain an appropriate position in the water.
The shell grew continuously throughout the animal’s life. New shell material was added at the open end, while additional septa were constructed behind the living chamber. This growth process produced the familiar spiral form and preserved changes in ribbing and whorl proportions as the ammonite matured.
Scissum Bed and Aalenian Biostratigraphy
The Scissum Bed takes its name from Tmetoceras scissum, the characteristic ammonite associated with this part of the succession. Comparable British sections describe it as a hard, sandy limestone that can contain a rich ammonite fauna indicative of the Aalenian Scissum interval.
Ammonites are highly valuable index fossils because many species evolved rapidly and were distributed widely through Jurassic seas. Their appearance, abundance and disappearance through successive rock layers allow palaeontologists to divide the geological record into zones, subzones and biohorizons.
A fossil with recorded bed information therefore carries greater scientific context than an ammonite known only from a broad locality. This specimen can be connected with a specific part of the early Middle Jurassic marine succession and with an interval named after the species it represents.
Inferior Oolite Geology at Burton Bradstock
The Inferior Oolite is a varied Middle Jurassic marine succession dominated by limestone, with sandy, ferruginous, bioclastic and locally oolitic deposits. The word “oolite” refers to rock containing ooids, which are small rounded carbonate grains formed as calcium carbonate accumulated around tiny nuclei such as sand grains or shell fragments.
The succession at Burton Bradstock is unusually condensed. Thin beds can represent substantial intervals of geological time, and surfaces between them may record periods of slow sedimentation, erosion or non-deposition. The local sequence includes fossiliferous horizons spanning parts of the Aalenian and Bajocian stages.
The Scissum Bed represents the older Aalenian part of this sequence. Its sandy limestone accumulated in a marine setting where currents, sediment supply and seabed conditions varied through time. Ammonites lived in the surrounding water alongside other cephalopods, while bivalves, brachiopods, gastropods, echinoids and burrowing organisms occupied the seabed.
Fossilisation in the Jurassic Sea
After the ammonite died, its shell descended to the seafloor. Soft tissues decayed, while sediment could enter the body chamber and any damaged internal chambers. Continued burial compacted the seabed deposits and eventually transformed them into solid rock.
During this process, the original shell could be mineralised, replaced or dissolved. Sediment hardened inside the shell to form a natural internal mould, preserving the ammonite’s overall shape and rib pattern even where much of the original shell material no longer survived.
Any surrounding matrix, colour variation, mineral staining, incomplete shell areas or surface irregularities are genuine features of this approximately 174-million-year-old fossil and form part of its geological character.
Burton Bradstock, Dorset
Burton Bradstock is a celebrated fossil locality on Dorset’s Jurassic Coast. The cliffs expose the Bridport Sand Formation beneath a condensed Inferior Oolite succession containing numerous fossiliferous horizons. Tmetoceras scissum is particularly associated with the early Aalenian Scissum Bed at this locality.
The area has long attracted geological study because its rocks preserve an important record of changing marine environments and ammonite communities. Fossils with a precise Burton Bradstock and Scissum Bed provenance are desirable additions to regional Dorset collections and displays illustrating Jurassic biostratigraphy.
Authentic British Jurassic Fossil
This genuine Tmetoceras scissum ammonite is ideal for a collection of British fossils, Aalenian ammonites, Dorset Jurassic specimens or Inferior Oolite marine life. Its distinctive ribbed form, named Scissum Bed provenance and recognised species identification provide strong scientific, educational and display interest.
This is a carefully chosen individual piece, and the photograph shows the actual fossil you will receive, rather than a representative example. Natural variations, attached matrix, mineral deposits, weathering and incomplete areas are authentic characteristics of the specimen.
Full sizing is shown in the photographs.
This fossil is a 100% genuine specimen and includes a generic Certificate of Authenticity card with a lifetime guarantee.
Reviews
There are no reviews yet.