Dumortieria Ammonite Fossil Jurassic Cotswolds UK Genuine British Ammonite Collector Specimen Natural History Display Fossil

Description

Genuine Dumortieria Ammonite Fossil from the Cotswolds, UK

This authentic Dumortieria fossil ammonite originates from the Cotswold Sands Formation of the Cotswolds in Gloucestershire, United Kingdom, and dates to the Lower Jurassic Period during the Toarcian Stage, approximately 182–174 million years ago. Ammonites of this genus are classic fossils from Early Jurassic marine sediments and represent extinct cephalopods that once thrived in the warm seas covering much of what is now Britain.

The specimen is a carefully chosen natural fossil, preserved within its original sedimentary matrix and displaying the distinctive coiled shell morphology typical of ammonites. The photographs show the exact fossil you will receive, ensuring collectors can view the preserved features and natural character of the specimen.

This fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming that the ammonite is a genuine fossil specimen. Please refer to the listing photographs for full sizing and scale, which clearly display the specimen offered.

Geological Origin – Cotswold Sands Formation

The fossil comes from the Cotswold Sands Formation, a Lower Jurassic sedimentary unit exposed throughout parts of Gloucestershire and the wider Cotswold Hills region. These rocks were deposited during the Toarcian Stage of the Early Jurassic, when southern Britain was submerged beneath a shallow epicontinental sea.

The Cotswold Sands consist primarily of sandy marine sediments and sandstones, representing environments where sand accumulated along the sea floor in relatively shallow marine conditions. These sediments formed within warm seas that supported diverse marine life.

The Early Jurassic deposits of the Cotswolds preserve a rich fossil assemblage including:

• Ammonites
• Bivalves and gastropods
• Belemnites
• Echinoderms
• Marine fish remains

These fossils provide valuable evidence of the marine ecosystems that existed during the Early Jurassic period.

Species Identification and Scientific Classification

The ammonite belongs to the genus Dumortieria, a well-known group of Jurassic ammonites commonly associated with Toarcian-aged strata. Dumortieria species are important biostratigraphic index fossils, frequently used by geologists to identify and correlate Early Jurassic rock layers.

Scientific Classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Subclass: Ammonoidea
• Order: Ammonitida
• Superfamily: Hildoceratoidea
• Family: Hildoceratidae
• Genus: Dumortieria

The genus Dumortieria was named in honour of the French palaeobotanist Barthélemy Charles Dumortier, reflecting the tradition of commemorating prominent scientists in taxonomic naming.

Dumortieria ammonites are characteristic fossils of the Dumortieria ammonite biozone, a key subdivision of the Toarcian stage used in Jurassic stratigraphy.

Shell Morphology and Structural Features

Ammonites possessed a distinctive planispiral coiled shell, which was divided internally into chambers used to regulate buoyancy. The living animal occupied the outermost chamber, while earlier chambers were separated by thin partitions known as septa.

Typical morphological features of Dumortieria ammonites include:

• Moderately evolute shell coiling
• Strong, evenly spaced ribbing along the shell whorls
• Rounded whorl sections with well-defined ribs
• Fine suture patterns where septa meet the shell wall
• Spiral geometry that allowed stable movement through water

The ribbed shell structure strengthened the shell while also producing the characteristic sculptured appearance seen in many Jurassic ammonites.

Early Jurassic Marine Environment

During the Toarcian Stage, the seas covering the Cotswolds formed part of a broad marine basin across Europe. These warm shallow seas supported abundant marine life and diverse ecosystems.

Within this environment, ammonites such as Dumortieria functioned as active marine predators. Their tentacles likely captured prey including:

• Small crustaceans
• Planktonic organisms
• Juvenile fish
• Other small marine invertebrates

The marine ecosystem also included numerous other organisms such as:

• Belemnites swimming through the water column
• Bivalves and gastropods living on the seabed
• Marine reptiles in nearby deeper waters
• Various echinoderms inhabiting the sea floor

Ammonites were a key part of these ecosystems and are among the most common fossils preserved within Jurassic marine sediments.

Fossilisation and Preservation

After the ammonite died, its shell sank to the sea floor and became buried within marine sediments. Over millions of years, sediment compaction and mineral replacement preserved the shell structure within the surrounding rock.

In many cases the original shell material dissolved and was replaced by minerals, while the overall structure of the shell remained preserved. The ribbing, coiling, and internal chamber structure often remain visible in the fossilised specimen.

This process allows ammonite fossils to retain their distinctive form even after nearly 180 million years of geological history.

Certificate of Authenticity

This fossil specimen includes a Certificate of Authenticity lifetime guarantee generic card, confirming that the ammonite is a genuine fossil.

Each fossil is carefully selected to ensure collectors receive an authentic example of prehistoric marine life.

A Classic Jurassic Ammonite from the Cotswolds

Ammonites from the Cotswold Sands Formation are valued among collectors due to their geological significance and association with the rich Early Jurassic marine fossil record of Britain.

This Dumortieria ammonite fossil from Gloucestershire represents a genuine piece of Jurassic marine history and offers collectors the opportunity to own a fossil from the ancient seas that once covered the Cotswold region nearly 180 million years ago.