Description
Brasilia bradfordensis Ammonite Fossil – Aalenian Stage, Jurassic, Horn Park, Dorset, United Kingdom
This impressive 6.5-inch Brasilia bradfordensis ammonite fossil is a striking and scientifically important specimen from the Aalenian Stage of the Middle Jurassic, collected from the world-renowned Horn Park Quarry, near Beaminster, Dorset, England. It comes from the highly regarded Alice Purnell Collection, known for its exceptional and meticulously documented British Jurassic fossils. The photo shows the exact specimen you will receive, with a 1cm scale cube included for accurate sizing reference. This ammonite represents an iconic fossil from Britain’s geological heritage, beautifully preserved and showcasing the elegance of Jurassic cephalopod life.
Geological Context and Provenance
The Horn Park Quarry is one of Britain’s most significant fossil localities and was the first geological nature reserve established in the UK, designated in 1954 for its unique palaeontological importance. The site exposes strata of the Inferior Oolite Group, representing sediments deposited during the Aalenian Stage (approximately 174–170 million years ago) of the Middle Jurassic Period.
During this time, much of what is now southern England was covered by a shallow, tropical sea that formed part of the northern margin of the Tethys Ocean. The seafloor accumulated fine carbonate-rich sediments in an environment dominated by oolitic limestones and calcareous muds. These ideal depositional conditions allowed for the exceptional preservation of marine organisms, including ammonites, belemnites, brachiopods, and bivalves.
The Brasilia bradfordensis ammonite is one of the most distinctive species from this region, frequently used as a biostratigraphic marker for identifying Aalenian-aged rocks across Europe.
Scientific Classification
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Kingdom: Animalia
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Phylum: Mollusca
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Class: Cephalopoda
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Order: Ammonitida
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Superfamily: Hammatocerataceae
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Family: Graphoceratidae
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Genus: Brasilia
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Species: Brasilia bradfordensis (S.S. Buckman, 1892)
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Geological Stage: Aalenian (Middle Jurassic)
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Locality: Horn Park Quarry, Beaminster, Dorset, England, UK
This species was first described by the eminent British palaeontologist Sydney Savory Buckman (1892), whose extensive work on Jurassic ammonites remains a cornerstone of ammonite biostratigraphy. Brasilia bradfordensis is particularly significant in the Bradfordensis Zone of the Aalenian, forming an index species that helps define the stage boundaries within the Inferior Oolite stratigraphy.
Morphology and Diagnostic Features
This specimen of Brasilia bradfordensis exhibits the classic planispiral coiling typical of the Graphoceratidae, with narrow, involute whorls and a relatively small umbilicus. The shell surface displays fine, closely spaced ribs that radiate from the umbilical margin and gently curve toward the venter. These ribs are occasionally bifurcate, branching subtly along the flanks before fading smoothly over the outer edge.
The venter (outermost margin) is slightly rounded, contributing to the ammonite’s streamlined hydrodynamic shape, while the flanks are gently compressed, giving the specimen a refined, symmetrical form. The ribbing pattern is both regular and delicate, providing a clear diagnostic feature distinguishing Brasilia from other contemporary ammonite genera such as Graphoceras or Leioceras.
The chambers of the ammonite’s internal shell were used to control buoyancy, allowing it to navigate through the open waters as an active, fast-swimming predator. Its elegant shell form suggests adaptation to a nektonic lifestyle, moving freely in the upper layers of the ancient Jurassic seas.
Depositional Environment and Biozone Context
The Aalenian Stage marks a pivotal period in Jurassic marine history, representing a transition between the Toarcian and Bajocian stages. The Horn Park limestones were formed in a warm, shallow marine shelf environment, characterised by stable conditions, moderate energy, and prolific carbonate sedimentation.
The Bradfordensis Zone, named after Brasilia bradfordensis, is a well-established ammonite biozone recognised across western Europe. Fossils from this zone provide invaluable insights into marine faunal evolution, palaeoclimate, and palaeogeography during the early Middle Jurassic. The presence of Brasilia bradfordensis in these strata marks an important chronostratigraphic interval within the Inferior Oolite succession.
Other fossils commonly found alongside Brasilia bradfordensis include belemnites, brachiopods, and echinoids, reflecting the rich biodiversity of the Aalenian marine ecosystem.
Provenance – The Alice Purnell Collection
This ammonite comes from the distinguished Alice Purnell Collection, a private collection renowned for its scientific rigour, authenticity, and detailed provenance. Specimens from this collection are highly sought after for their precise locality records, careful preparation, and aesthetic quality. The Brasilia bradfordensis offered here is a particularly fine example, representing both a scientifically significant species and a collector-grade display fossil.
Authenticity and Presentation
All of our fossils are 100% genuine specimens and come with a Certificate of Authenticity, verifying their geological age, species identification, and provenance. The photograph shows the actual specimen you will receive, with a 1cm scale cube for reference. Each piece is selected for its preservation quality, visual appeal, and scientific importance.
A Classic British Jurassic Ammonite
This 6.5-inch Brasilia bradfordensis ammonite fossil from Horn Park, Dorset, is an exceptional representative of Britain’s Aalenian ammonite fauna. Its fine ribbing, elegant coiling, and historical provenance from the Alice Purnell Collection make it an outstanding specimen for collectors, educators, or enthusiasts of natural history. Formed over 170 million years ago in the ancient Jurassic seas, it stands as a timeless reminder of the beauty, diversity, and scientific significance of Earth’s deep geological past.
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