Description
Iridescent Psiloceras Ammonite Fossil from the Blue Lias of Somerset
This beautiful iridescent Psiloceras ammonite fossil originates from the famous Blue Lias Formation at Doniford Bay near Watchet, Somerset, United Kingdom. Dating to the Early Jurassic Period, specifically the Hettangian Stage approximately 201–199 million years ago, this fossil represents one of the earliest ammonites to appear following the end-Triassic extinction event
Psiloceras is one of the most important ammonite genera in Jurassic stratigraphy. It serves as a key index fossil marking the base of the Jurassic System, appearing within the Psiloceras planorbis Biozone, which is internationally recognised as the boundary that defines the beginning of the Jurassic Period.
The specimen displays a natural iridescent surface sheen, a beautiful preservation effect sometimes seen in ammonites from the Blue Lias. This shimmering effect results from the preservation of the original shell layers, producing subtle colour reflections across the fossil surface that make specimens particularly striking for collectors.
Geological Formation and Stratigraphic Context
The fossil comes from the Blue Lias Formation, a classic sequence of alternating limestone and shale layers deposited across southern Britain during the earliest Jurassic. These sediments are well exposed along the Somerset coastline, particularly at Doniford Bay near Watchet, where fossil ammonites, marine reptiles, and other invertebrates are regularly discovered.
The Blue Lias represents deposition within a shallow marine shelf environment bordering the ancient Tethys Ocean. Fine calcareous muds and carbonate sediments accumulated on the seabed in relatively calm conditions, periodically interrupted by changes in sediment supply that produced the distinctive rhythmic limestone and shale layering.
Within these sediments, ammonites such as Psiloceras thrived and were preserved in remarkable detail. The fine-grained limestone layers often protected shell material from complete dissolution, allowing occasional preservation of iridescent shell layers.
Fossil Classification and Biological Background
Psiloceras belongs to the class Cephalopoda, subclass Ammonoidea, an extinct group of marine molluscs related to modern squids, octopuses, and nautiluses. Within ammonite classification, Psiloceras is placed in the order Ammonitida and family Psiloceridae.
The genus was first formally described by the French naturalist Alcide d’Orbigny, one of the pioneers of ammonite taxonomy and Jurassic stratigraphy.
Ammonites were active swimming predators or opportunistic feeders that inhabited marine environments throughout the Mesozoic Era. They possessed coiled shells divided into chambers, which helped regulate buoyancy through a system of gas-filled compartments connected by a tube called the siphuncle.
Psiloceras is particularly significant because it represents the earliest radiation of ammonites following the global extinction event at the end of the Triassic.
Shell Morphology and Notable Features
Psiloceras ammonites are known for their smooth, elegant shell morphology, which differs from many later ammonites that developed heavy ribbing or ornamentation.
Typical characteristics include:
- Smooth, planispiral shell coiling
- Rounded whorl cross-section
- Minimal ribbing or external ornamentation
- Clearly defined whorl expansion as the shell grows
- Delicate suture patterns marking internal chamber divisions
The simplicity of the shell design reflects early evolutionary forms within Jurassic ammonites. Specimens from the Blue Lias are often preserved with remarkable detail, sometimes showing the original shell structure responsible for iridescent reflections.
Early Jurassic Marine Environment
During the Hettangian Stage, southern Britain lay beneath a warm shallow sea that covered large parts of Europe. This marine basin supported a diverse ecosystem including ammonites, bivalves, belemnites, crustaceans, and early marine reptiles such as ichthyosaurs.
Ammonites such as Psiloceras were abundant in these seas and played an important role in marine food webs. Their rapid evolution and widespread distribution make them invaluable tools for dating Jurassic rock layers, allowing geologists to identify precise time intervals within the fossil record.
The Blue Lias sediments formed during this time preserve one of the most important Early Jurassic fossil assemblages in Europe.
Authentic Fossil Specimen
This fossil is a genuine Psiloceras ammonite from the Blue Lias Formation of Doniford Bay, Watchet, Somerset. The specimen has been carefully selected for its aesthetic appeal, preservation quality, and natural iridescent shell surface.
The photographs show the actual fossil specimen you will receive, ensuring authenticity and transparency for collectors.
Full sizing please see photo.
Certificate of Authenticity
This fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming that the specimen is a genuine natural fossil.
Psiloceras ammonites from the Blue Lias are highly valued due to their geological importance, beautiful preservation, and connection to the very beginning of the Jurassic Period. The natural iridescent shell preservation makes this specimen an especially attractive display piece and a remarkable addition to any fossil collection or geological exhibit.
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