Description
Rare Proplanulites koenigi Fossil Ammonite – Jurassic, Ashton Keynes, Wiltshire, UK
This exceptional Proplanulites koenigi ammonite fossil, measuring approximately 4.5 inches, is a beautifully preserved specimen from the Lower Callovian Stage of the Middle Jurassic, discovered in the Ashton Keynes area of Wiltshire, England. This ammonite originates from strata dating to around 164–166 million years ago, and represents one of the classic British ammonite forms of the Jurassic seas.
Sourced from the Alice Purnell Collection, this specimen exemplifies the high quality and scientific value associated with carefully curated historical collections. Its exceptional preservation showcases the intricate ribbing and coiling typical of the species Proplanulites koenigi, making it a desirable piece for collectors, educators, and fossil enthusiasts alike.
All of our Fossils are 100% Genuine Specimens and come with a Certificate of Authenticity. The fossil pictured is the exact specimen you will receive, photographed with a 1cm scale cube for accurate sizing.
Geological Context and Stratigraphy
This fossil was found within Lower Callovian deposits, part of the Jurassic sedimentary sequences that outcrop across southern England. The rocks of this age were deposited during the Middle Jurassic Period, roughly 165 million years ago, in what was once a warm, shallow marine environment teeming with life.
Specifically, the ammonite derives from layers that belong to the Cornbrash Formation, a sequence of limestones and marls formed in a low-energy epicontinental sea that extended over much of what is now Europe. These deposits represent the remains of marine sediments laid down in a subtropical sea, where ammonites such as Proplanulites koenigi thrived as active predators and planktonic drifters.
The Callovian Stage is divided into several biozones defined by distinctive ammonite species. Proplanulites koenigi is characteristic of the Koenigi Zone, making it a valuable biostratigraphic marker used by geologists and palaeontologists to correlate Jurassic rock layers across Europe.
Taxonomy and Scientific Classification
- Genus: Proplanulites
- Species: Proplanulites koenigi (Sowerby, 1815)
- Family: Perisphinctidae
- Superfamily: Perisphinctoidea
- Order: Ammonitida
- Class: Cephalopoda
- Phylum: Mollusca
- Age: Middle Jurassic (Lower Callovian Stage, Koenigi Zone)
- Formation: Cornbrash Formation
- Locality: Ashton Keynes, Wiltshire, United Kingdom
Morphological Characteristics
The genus Proplanulites is known for its planispiral, involute shell form with compressed whorls and prominent, evenly spaced ribbing that extends radially across the flanks. The ribs are sharp and well-defined, giving the shell a delicately sculptured appearance.
In this specimen, the ribbing is exceptionally well preserved, showing the gradual bifurcation and fine growth lines typical of the Perisphinctid ammonites. The venter (outermost edge) remains rounded and smooth, with no keels, reflecting its adaptation to moderate swimming in open marine waters.
The shell’s whorls are slightly overlapping, and its smooth inner coils can be clearly traced, providing a textbook example of Jurassic ammonite morphology. The fossil’s calcite preservation also reveals subtle mineral banding, with occasional iron oxide inclusions lending warm natural tones to the surface.
Palaeoenvironment and Fossilisation
During the Middle Jurassic, much of southern England, including the Wiltshire region, was submerged beneath a shallow sea connected to the Tethys Ocean. The seabed was composed of fine carbonate muds that accumulated slowly, allowing delicate ammonite shells to settle and become buried before significant decay or damage occurred.
The excellent preservation of this Proplanulites koenigi indicates that it was quickly entombed in fine-grained sediment, limiting exposure to scavengers and currents. Over millions of years, mineral replacement and lithification transformed the organic material into stone, preserving even fine shell details.
The result is a fossil that not only retains its original form and ornamentation but also provides valuable information about Jurassic marine ecosystems, depositional environments, and the evolutionary history of ammonites.
Scientific and Historical Importance
The genus Proplanulites occupies an important evolutionary position within the Perisphinctidae family, linking earlier planulate ammonites to later, more ornate forms found in the Oxfordian and Kimmeridgian stages. Its widespread distribution across Europe and clear zonal distinction make it a key species for biostratigraphic studies.
This particular specimen’s provenance from the Alice Purnell Collection adds both historical and scientific value. Private collections like this have long contributed to our understanding of British palaeontology and the detailed study of local geological formations.
The ammonite’s size (4.5″) and remarkable state of preservation make it a rare and desirable specimen—perfect for collectors seeking a standout fossil from Britain’s Jurassic heritage.
Aesthetic and Display Qualities
The fossil displays the timeless elegance typical of well-preserved ammonites. Its symmetrical spiral, combined with subtle natural mineralisation, makes it not only a scientifically valuable piece but also a visually captivating decorative object. When displayed under light, the ribbing casts fine shadows that accentuate its ancient geometry—nature’s perfect example of mathematical harmony in evolution.
Ideal for museum-style display, collector cabinets, educational use, or natural décor, this ammonite embodies both artistry and history.
Authenticity and Provenance
- Specimen: Proplanulites koenigi fossil ammonite
- Age: Lower Callovian, Middle Jurassic (~165 million years old)
- Formation: Cornbrash Formation
- Location: Ashton Keynes, Wiltshire, United Kingdom
- Collection: From the Alice Purnell Collection
- Condition: Professionally cleaned and preserved
- Authenticity: 100% Genuine Fossil – Certificate of Authenticity included
A Window into the Jurassic Seas of England
This rare 4.5″ Proplanulites koenigi ammonite from Ashton Keynes, Wiltshire, offers a direct connection to Britain’s Jurassic past. Preserved in remarkable detail, it reflects the beauty of natural history and the geological story of an age long vanished beneath ancient seas.
Whether you are a fossil collector, museum curator, or admirer of Earth’s deep history, this specimen stands as a tangible piece of prehistoric life — a golden spiral of time from the heart of the Jurassic world.
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