Description
Aulacostephanus pseudomutabilis Ammonite from Wiltshire, UK
This listing features a superb Aulacostephanus pseudomutabilis fossil ammonite, dating from the Lower Kimmeridgian stage of the Jurassic period, around 157 to 155 million years ago. Discovered in the Kimmeridge Clay deposits of Wiltshire, United Kingdom, this ammonite represents one of the most recognisable and scientifically important species from the British Jurassic. Each specimen we supply is carefully chosen and is accompanied by a Certificate of Authenticity, ensuring that it is a 100% genuine fossil. The photos show the actual ammonite for sale, with a 1 cm scale cube included for accurate size reference.
Geological Context: The Lower Kimmeridgian Stage
The Kimmeridgian stage forms part of the Late Jurassic epoch, renowned for its fossil-rich marine deposits that stretch across much of southern England. The Kimmeridge Clay Formation, which dominates the Jurassic exposures of Wiltshire, is a famous marine sedimentary unit composed primarily of dark shales and clays. These sediments were deposited in a low-oxygen offshore environment, which allowed for exceptional preservation of marine life, including ammonites, marine reptiles, bivalves, and gastropods.
The Lower Kimmeridgian is a key stratigraphic interval, with Aulacostephanus ammonites widely used as index fossils. Their presence allows geologists to date and correlate sedimentary layers across Europe. This makes specimens such as Aulacostephanus pseudomutabilis scientifically valuable as well as highly collectable.
Taxonomy and Classification
- Genus: Aulacostephanus
- Species: pseudomutabilis
- Family: Aulacostephanidae
- Superfamily: Perisphinctoidea
- Order: Ammonitida
- Age: Lower Kimmeridgian, Jurassic (c. 157–155 million years ago)
- Locality: Wiltshire, United Kingdom
Belonging to the Aulacostephanidae, these ammonites are closely related to other ribbed Jurassic forms within the Perisphinctoidea. Their distinct morphology has made them one of the most recognisable ammonite groups of the Late Jurassic.
Morphological Features
The shell of Aulacostephanus pseudomutabilis is characterised by:
- Strong, sharp ribbing radiating across the flanks.
- Regular tuberculation, with small nodes along the rib intersections.
- Involute to moderately evolute coiling, giving a balanced appearance with visible inner whorls.
- Compressed whorl section, enhancing the elegant ribbed pattern typical of the genus.
These features not only make the fossil striking in appearance but also give it strong identification markers, distinguishing it from other ammonites in the same formation.
Scientific and Collecting Importance
Specimens of Aulacostephanus pseudomutabilis are not only visually striking but also serve as important biostratigraphic tools. As index fossils, they help define zones within the Lower Kimmeridgian, making them essential to paleontological research. For collectors, this ammonite offers both historical and scientific significance, as it represents an iconic species from the British Jurassic.
Ammonites like this one also played a critical ecological role in the Jurassic seas, acting as fast-moving predators that fed on plankton and small marine animals. Their abundance and diversity highlight the evolutionary success of ammonites before their extinction at the end of the Cretaceous.
Key Details
- Fossil Type: Ammonite
- Species: Aulacostephanus pseudomutabilis
- Geological Age: Lower Kimmeridgian, Jurassic
- Location: Wiltshire, United Kingdom
- Family: Aulacostephanidae
- Authenticity: Guaranteed genuine with Certificate of Authenticity
- Display: Actual specimen as pictured, with scale cube for size reference
Authenticity and Guarantee
We take pride in offering only genuine fossils. This Aulacostephanus pseudomutabilis ammonite is an authentic specimen from the Kimmeridge Clay of Wiltshire and is supplied with a Certificate of Authenticity. Collectors and enthusiasts alike will appreciate the combination of visual appeal, historical context, and scientific importance that this ammonite provides.
A truly remarkable fossil, this ammonite is a lasting reminder of the Jurassic seas that once covered Britain, preserved for millions of years and now available for collectors and educational study.
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