Description
Genuine Streblites tenuilobatus Ammonite Fossil
This carefully chosen specimen is a genuine Streblites tenuilobatus ammonite fossil from Dorset, UK. It dates to the Lower Kimmeridgian Stage of the Upper Jurassic and represents an extinct marine cephalopod that inhabited the warm seas covering southern Britain approximately 155 million years ago.
Streblites tenuilobatus is a finely formed ammonite recognised for its relatively involute shell, compressed profile and delicate ornamentation. It belongs to the order Ammonitida and represents one of the elegant ammonite forms associated with Late Jurassic marine deposits.
Ammonites were highly successful molluscs related to living squid, cuttlefish, octopuses and nautiluses. They possessed chambered external shells that provided protection and buoyancy, allowing them to occupy a wide range of marine habitats throughout the Mesozoic Era.
The combination of species-level identification, Lower Kimmeridgian age and British provenance gives this specimen strong geological, educational and collection interest. It is particularly suitable for collectors of Dorset fossils, Upper Jurassic ammonites and authentic British palaeontological specimens.
Distinctive Ammonite Shell Morphology
The shell of Streblites tenuilobatus was planispirally coiled, with successive whorls developing within a single plane around the central umbilicus. The shell is comparatively involute, meaning that the later whorls overlap and conceal much of the earlier growth.
Its whorls are generally compressed from side to side, producing a streamlined and elegant profile. The outer margin, or venter, may be narrow and clearly defined, while the flanks can display subtle ribs, growth striae or fine spiral ornament depending on the individual growth stage and preservation.
The species name “tenuilobatus” refers to slender or finely developed lobes, a feature associated with the intricate suture pattern formed where the internal chamber walls met the outer shell. These complex sutures strengthened the shell while also providing palaeontologists with valuable features for classification.
Depending on preservation, this specimen may display the central umbilicus, overlapping whorls, delicate surface sculpture, the narrow venter, portions of the body chamber or traces of the chambered phragmocone. Natural wear, incomplete edges, mineral-filled fractures and attached matrix are normal features of an authentic Jurassic fossil.
Chambered Shell and Buoyancy System
Internally, the ammonite shell was divided by curved walls called septa. These created a series of chambers collectively known as the phragmocone. The living animal occupied only the final and largest section of the shell, known as the body chamber.
A narrow tube called the siphuncle passed through the chambers. By regulating the balance of liquid and gas within them, the ammonite could control its buoyancy and maintain a suitable position within the water column.
The soft-bodied animal extended from the shell aperture and probably possessed arms surrounding a hard, beak-like mouth. Movement was achieved by drawing water into the mantle cavity and expelling it through a muscular funnel, producing a form of jet propulsion similar to that used by living cephalopods.
The compressed shell of Streblites tenuilobatus may have provided a relatively hydrodynamic form, allowing controlled movement through the Jurassic sea. Its shell ornament and proportions changed gradually as the ammonite matured, recording successive stages of growth.
Life in the Lower Kimmeridgian Sea
During the Lower Kimmeridgian, the region now forming Dorset lay beneath an extensive shallow to moderately deep marine environment. The modern coastline, cliffs and countryside did not yet exist, and warm seawater covered large areas of southern Britain.
Streblites tenuilobatus shared this environment with other ammonites, belemnites, bivalves, gastropods, brachiopods, echinoids, crustaceans, fish and marine reptiles. These organisms occupied habitats ranging from the sediment-covered seabed to the open water above it.
The ammonite was probably an active predator or opportunistic feeder. It may have consumed small crustaceans, planktonic animals, juvenile molluscs and other suitably sized prey. Ammonites themselves formed part of the food web and were hunted by larger fish and marine reptiles.
After death, the soft tissues decomposed and the empty shell descended towards the seabed. Sediment could enter the body chamber and any damaged internal chambers. If the shell was buried before being destroyed by currents, scavengers or dissolution, its form could be preserved within the accumulating marine sediment.
Lower Kimmeridgian Geology
The Kimmeridgian is a stage of the Upper Jurassic Period and takes its name from Kimmeridge in Dorset. Rocks of this age are internationally important and preserve a detailed record of Late Jurassic marine environments.
Kimmeridgian deposits in southern England include mudstone, clay, marl and limestone. These different rock types record variations in water depth, oxygen levels, carbonate production and the supply of sediment from surrounding land areas.
Fine mud and clay accumulated under relatively quiet marine conditions, while limestone formed from carbonate mud and the skeletal remains of marine organisms. Organic-rich beds could develop where large amounts of biological material reached the seabed and decomposition occurred under restricted oxygen conditions.
Ammonites are especially useful for interpreting Kimmeridgian geology because their forms changed rapidly through time. Distinctive ammonite assemblages allow geologists to compare separate rock sequences and divide them into detailed biostratigraphical zones.
The preservation of this specimen records a long sequence of natural events beginning with shell growth in the Jurassic sea, followed by death, burial, compaction, mineralisation, uplift and eventual exposure through erosion.
Dorset Fossil Provenance
Dorset is internationally celebrated for its Jurassic geology and fossil heritage. Its sedimentary rocks preserve evidence of changing marine ecosystems across a substantial part of the Jurassic Period.
A recorded Dorset provenance gives this specimen important geographical and geological context. It connects the ammonite directly with one of Britain’s most significant fossil-producing regions rather than identifying it only as a general Upper Jurassic specimen.
The species is more frequently associated with continental European Jurassic deposits, making a recorded Dorset example particularly interesting within a collection of British ammonites. Its combination of elegant shell morphology, Lower Kimmeridgian age and UK provenance makes it well suited to collections focused on ammonites, Dorset geology, British fossils, extinct cephalopods or Upper Jurassic marine life.
Authentic Fossil with Certificate of Authenticity
This is a genuine natural fossil and not a replica, cast or manufactured reproduction. Its coiled form, surface detail, colour and preservation result from the original Streblites tenuilobatus shell and the natural geological processes it experienced over millions of years.
The photograph shows the actual carefully chosen specimen you will receive. Please examine the supplied images closely, as they provide the best record of its exact condition, preserved ornament, matrix and individual appearance.
Full sizing please see photo.
The fossil includes a generic Certificate of Authenticity card supported by our lifetime guarantee of authenticity.
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