Description
Genuine Shirbuirnia trigonalis Ammonite Fossil
This listing is for a genuine Shirbuirnia trigonalis ammonite fossil from the Inferior Oolite Group at Sherborne, Dorset, UK. It dates to the Middle Jurassic, Bajocian stage, specifically the Sowerbyi Zone, making it a highly collectable British Jurassic ammonite with excellent geological and palaeontological interest. This carefully chosen fossil is a genuine specimen and includes a Certificate of Authenticity lifetime guarantee generic card.
The photograph shows the actual fossil specimen you will receive, so the piece pictured is the exact fossil supplied. Full sizing details can be seen in the photo. This specimen is ideal for collectors of British fossils, Jurassic ammonites, Dorset fossils, Inferior Oolite specimens, natural history displays, and educational geology collections.
Species and Fossil Type
Shirbuirnia trigonalis is an ammonite, an extinct marine cephalopod related to modern squid, cuttlefish, octopus, and nautilus. Ammonites possessed coiled, chambered shells, with the living animal occupying the outer body chamber while the inner chambers helped regulate buoyancy. Their distinctive spiral shells make them one of the most recognisable fossil groups, while their rapid evolution makes them especially valuable for dating Jurassic rocks.
The genus Shirbuirnia is associated with Middle Jurassic ammonite faunas and is of particular interest to collectors who specialise in classic British ammonites from the Inferior Oolite. The species name trigonalis reflects a form traditionally associated with a more angular or triangular impression in shell shape or ornament, depending on preservation. Fossils of this type are valued for their combination of attractive form, local provenance, and precise stratigraphic age.
Middle Jurassic Bajocian Age
This fossil dates to the Bajocian stage of the Middle Jurassic Period. During the Bajocian, warm shallow seas covered much of what is now southern England. These marine environments supported a rich ecosystem of ammonites, belemnites, bivalves, brachiopods, gastropods, echinoids, crinoids, fish, and marine reptiles.
Ammonites from the Bajocian are especially important in geology because they are widely used as index fossils. Their changing shell forms and species distributions allow geologists to divide Jurassic marine deposits into detailed zones and subzones. This specimen is recorded from the Sowerbyi Zone, an important ammonite biozone within the Bajocian, giving it additional scientific and collectable interest beyond its visual appeal.
Inferior Oolite Group and Sowerbyi Zone
The Inferior Oolite Group is one of the most famous Middle Jurassic rock sequences in southern England. It is known for fossil-rich limestones and related marine sediments deposited in warm, shallow sea conditions. These rocks preserve a wide variety of marine invertebrates and are particularly well known for their ammonites.
The Sowerbyi Zone is a recognised ammonite zone within the Bajocian and helps place this fossil into a more precise geological interval. Fossils with zone-level information are especially attractive to collectors because they carry clear stratigraphic context. This makes the specimen useful not only as a display fossil but also as a piece of geological history from a specific period in the development of Jurassic marine life.
Sherborne, Dorset Locality
Sherborne in Dorset is part of a classic region for British Jurassic fossils. The surrounding geology preserves evidence of ancient marine conditions, changing sea levels, and rich sea-floor communities from the Middle Jurassic. Fossils from Dorset are popular with collectors because of their strong UK provenance, historic fossil localities, and connection to the wider Jurassic geology of southern England.
A fossil from Sherborne offers a direct link to the warm Jurassic seas that once covered this part of Britain. Over millions of years, ammonite shells settled into sediment, were buried, mineralised, and preserved within the rock record. Today, these fossils provide a tangible record of prehistoric marine ecosystems and the animals that lived within them.
Morphology and Collectable Features
Shirbuirnia trigonalis ammonites are appreciated for their classic coiled ammonite form and collectable Jurassic character. Depending on preservation, specimens may show visible whorl structure, ribbing, a defined umbilicus, natural shell texture, mineralised detail, and surrounding matrix from the Inferior Oolite. The combination of spiral form and geological context makes this fossil appealing for both study and display.
As a genuine natural fossil, this specimen may show normal signs of age and preservation, including mineralisation, matrix attachment, surface texture, small chips, repairs, weathering, compression, or natural colour variation. These features are typical of authentic fossils and form part of the individual character of the piece. This is not a modern replica, cast, or decorative imitation.
Provenance and Authenticity
Fossil type: Ammonite
Species: Shirbuirnia trigonalis
Age: Middle Jurassic, Bajocian
Biozone: Sowerbyi Zone
Geological group: Inferior Oolite Group
Locality: Sherborne, Dorset, UK
Certificate: Includes a Certificate of Authenticity lifetime guarantee generic card
Specimen shown: The photo shows the actual fossil you will receive
Size: Full sizing shown in the photo
This Shirbuirnia trigonalis ammonite fossil is a carefully selected genuine British Jurassic specimen with strong appeal for fossil collectors, geology enthusiasts, educational collections, and display cabinets. Its Bajocian age, Sowerbyi Zone detail, Inferior Oolite origin, Dorset locality, and included Certificate of Authenticity make it a desirable addition to any collection of genuine ammonites, UK fossils, prehistoric marine life, or Middle Jurassic natural history specimens.
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