Catasigaloceras planicerclus Double Ammonite Fossil Male and Female Kellaways Beds Jurassic Latton Quarry UK

Description

Geological Context and Provenance

This exceptional specimen represents a double ammonite fossil of Catasigaloceras planicerclus, discovered in the Kellaways Beds, Callovian Stage of the Middle Jurassic, approximately 166 – 163 million years ago. It was unearthed at Latton Quarry in the Cotswold Water Park, near Swindon, United Kingdom, a locality celebrated for its richly fossiliferous deposits.

The Kellaways Beds are part of the Great Oolite Group and are comprised of sandy clays and fine-grained sediments laid down in a shallow marine environment. These strata are particularly renowned for yielding abundant ammonite faunas, including Catasigaloceras, which serve as vital index fossils for the Callovian and provide an important window into the palaeoecology of Jurassic seas.

Fossil Type and Species Information

Catasigaloceras planicerclus belongs to the Order Ammonitida, Superfamily Stephanoceratoidea, and Family Parkinsoniidae. Members of this group are noted for their ornate, ribbed shells and evolute coiling. This fossil is especially significant because it preserves both the macroconch (female) and microconch (male) forms together, providing an excellent demonstration of sexual dimorphism in ammonites.

The macroconch typically displays larger, more robust whorls suited for egg production, while the microconch is smaller, more compact, and often associated with features related to reproductive strategies. Having both forms preserved together in a single specimen is relatively uncommon and enhances both its scientific and collector value.

Morphological Features

This fossil exhibits the key identifying traits of Catasigaloceras planicerclus:

• Evolute Coiling – The whorls are open, with earlier whorls visible across the coiled structure.
• Regular Ribbing – Strong, even ribs radiate across the flanks, extending over the venter to create a distinctive ornamental pattern.
• Planicerclus Profile – The flattened shell outline is characteristic of this species.
• Sexual Dimorphism – Presence of both macroconch and microconch forms within the same piece, offering a rare visual comparison of male and female forms.

These striking features are not only diagnostic of the species but also create a naturally aesthetic specimen that highlights the beauty of Jurassic ammonites.

Depositional Environment

During the Callovian, the region now known as the Cotswolds and Swindon lay beneath a shallow epicontinental sea connected to the Tethys Ocean. The seabed consisted of fine sediments deposited in a calm marine environment, supporting a thriving ecosystem of ammonites, belemnites, bivalves, gastropods, and marine reptiles.

The exceptional preservation seen in specimens from the Kellaways Beds results from rapid burial in these soft sediments, protecting ammonite shells from extensive damage and allowing their detailed ribbing and coiling to be retained.

Collector and Scientific Importance

This double Catasigaloceras planicerclus ammonite fossil represents an outstanding piece for both collectors and researchers:

• Scientific Value – Demonstrates sexual dimorphism in ammonites with both male and female shells preserved together.
• Display Quality – Strong ribbing, well-preserved coiling, and clear morphological features.
• Historical Locality – From Latton Quarry, one of the most important Jurassic fossil sites in southern England.

Authenticity and Presentation

• 100% Genuine Specimen – Supplied with a Certificate of Authenticity.
• Exact Fossil Shown – Photographs depict the actual specimen you will receive.
• Scale Reference – Scale rule squares / cube = 1 cm. Please refer to photos for full sizing.

This remarkable Catasigaloceras planicerclus double ammonite fossil, with both macroconch and microconch forms, is a rare opportunity to own a scientifically significant and visually striking specimen from the Callovian of Gloucestershire, a true showcase of Jurassic marine life.