Description
Genuine Streblites tenuilobatus Ammonite Fossil
This genuine ammonite fossil is identified as Streblites tenuilobatus and originates from the Dorset Coast in Dorset, United Kingdom. It was preserved within the Kimmeridge Clay Formation and dates from the Kimmeridgian Stage of the Upper Jurassic Period.
Streblites tenuilobatus is an elegant ammonite recognised for its compressed shell form, streamlined whorls and comparatively refined ornamentation. It represents an extinct marine cephalopod that inhabited the Jurassic seas covering southern Britain approximately 150 million years ago.
This carefully chosen fossil is the exact specimen shown in the listing photographs. Its natural shape, preservation, colour, matrix and individual geological characteristics can therefore be inspected before purchase. Full sizing and scale information are provided in the photographs.
Species Identification and Classification
The species was originally described by the German palaeontologist Albert Oppel in 1863. Its scientific classification places it among the advanced ammonites that diversified extensively during the Late Jurassic.
Scientific classification includes:
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Subclass: Ammonoidea
Order: Ammonitida
Superfamily: Haploceratoidea
Family: Oppeliidae
Subfamily: Streblitinae
Genus: Streblites
Species: Streblites tenuilobatus
Species authority: Oppel, 1863
Ammonites were related to living squid, cuttlefish, octopuses and nautiluses. Although their external shells superficially resemble those of the modern chambered nautilus, ammonites formed a separate and highly diverse evolutionary group that became extinct at the end of the Cretaceous Period.
Distinctive Streblites Shell Morphology
Streblites tenuilobatus typically possessed a tightly coiled and strongly involute shell. In involute ammonites, each new whorl substantially overlaps the previous one, leaving only a small central umbilicus visible.
The whorls are generally compressed from side to side, creating a relatively slender and streamlined profile. The venter, or outer edge of the shell, may appear narrow or sharpened, particularly when compared with the broad, rounded venters of more robust ammonite groups.
Surface ornamentation can include fine ribs, subtle folds and delicate spiral features. These markings may become stronger or weaker at different growth stages. The degree of visible detail also depends on whether the specimen preserves original shell material, an external impression, a sediment-filled internal mould or a combination of these forms.
The species name tenuilobatus refers to slender or delicate lobes, reflecting features associated with the complex suture pattern. Suture lines formed where the internal chamber walls met the outer shell and are important characteristics used in ammonite classification.
Chambered Shell and Marine Lifestyle
The ammonite shell was divided internally by curved partitions called septa. These created a series of chambers connected by a narrow tube known as the siphuncle. The living animal occupied the final and largest body chamber, while the earlier chambers formed part of its buoyancy system.
By regulating the balance of liquid and gas within the chambers, the ammonite could maintain its position in the water. The compressed and hydrodynamic form of Streblites suggests an ammonite adapted to movement within the marine water column.
The animal would have extended its head, eyes and muscular arms from the shell opening. It may have fed upon small marine organisms, planktonic animals or organic material encountered while moving through the sea.
Kimmeridgian Upper Jurassic Age
This fossil dates from the Kimmeridgian Stage of the Upper Jurassic. The Kimmeridgian followed the Oxfordian and preceded the Tithonian, representing an interval of Late Jurassic time from approximately 154 to 149 million years ago.
The stage takes its name from Kimmeridge in Dorset, where the characteristic sedimentary rocks are exceptionally well exposed. This makes fossils from the Dorset Coast especially significant because they come from the geographical region associated with the original definition of the Kimmeridgian.
Ammonites evolved rapidly and many species existed for limited intervals of geological time. They are therefore important index fossils used by geologists to date and correlate marine sedimentary rocks.
Streblites tenuilobatus is strongly associated with Kimmeridgian ammonite successions and has given its name to the Tenuilobatus Zone in parts of Europe. Its occurrence is therefore important in the biostratigraphic study of Upper Jurassic marine deposits.
Kimmeridge Clay Formation Geology
The Kimmeridge Clay Formation is one of Britain’s most important Upper Jurassic geological units. It consists primarily of dark grey mudstones, shales, organic-rich clays and occasional bands of limestone or carbonate-rich concretions.
These sediments accumulated slowly on the floor of a warm, relatively deep epicontinental sea. Fine mud settled through the water column, while large quantities of organic material were deposited and preserved within the seabed sediment.
At times, oxygen levels near the sea floor were reduced. These low-oxygen conditions limited scavenging and biological disturbance, helping preserve shells, bones and other remains. The formation is particularly famous for ammonites, belemnites, bivalves, marine reptiles, fish, crustaceans and fossil wood.
The organic-rich nature of parts of the Kimmeridge Clay also makes the formation economically and scientifically important. Its sediments are regarded as a major source rock for petroleum systems beneath the North Sea.
Late Jurassic Marine Environment
During the Kimmeridgian, the area now forming Dorset lay beneath a broad marine basin. The climate was considerably warmer than today, and high sea levels covered much of southern Britain.
Ammonites shared these waters with belemnites, nautiloids, bivalves, gastropods, brachiopods, fish and marine reptiles including ichthyosaurs, plesiosaurs and pliosaurs. Microscopic plankton supported the wider food web and contributed organic material to the sediment below.
The relatively fine-grained nature of the Kimmeridge Clay records a generally quiet offshore environment. Periodic changes in water circulation, oxygen availability, biological productivity and sediment supply produced the alternating beds now visible along the Dorset Coast.
Fossilisation and Natural Preservation
After the ammonite died, its shell descended to the seabed and was gradually covered by fine marine sediment. The soft tissues decomposed, while mud entered the empty shell and filled some or all of its chambers.
Continued burial compacted the surrounding sediment and transformed it into rock. The original shell, composed largely of aragonite, could dissolve, recrystallise or be replaced by other minerals. Sediment hardened inside the shell to preserve an internal mould, while surviving exterior material retained parts of the original ornament.
Natural fractures, incomplete edges, areas of matrix, mineral deposits, pressure marks, weathering and colour variations are expected features of a genuine Kimmeridge Clay fossil. They record the specimen’s long geological history and make every example unique.
Dorset Coast Fossil Provenance
The Dorset Coast forms part of the internationally renowned Jurassic Coast, celebrated for its exceptional sequence of Triassic, Jurassic and Cretaceous rocks. Coastal erosion continually exposes new sections of the Kimmeridge Clay Formation and occasionally reveals fossils that have remained enclosed within the cliffs for millions of years.
Fossils from recorded Dorset localities are especially desirable because their geological and geographical provenance is retained. This specimen combines an identifiable ammonite species with a recognised formation, geological stage and classic British fossil region.
Actual Specimen and Certificate of Authenticity
This is a genuine fossil specimen and not a cast, replica or artificial reproduction. The listing photographs show the actual Streblites tenuilobatus ammonite that will be supplied, allowing you to examine its shell form, preservation, matrix, colour and natural surface characteristics before purchasing.
Full sizing is shown in the photographs.
The fossil includes a generic Certificate of Authenticity card carrying a lifetime guarantee. Its refined oppeliid morphology, Kimmeridgian age, Kimmeridge Clay provenance and connection with the historic Dorset Coast make it an excellent addition to a British fossil collection, Jurassic ammonite display, natural-history cabinet or educational geological collection.
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