Yorkshire Ammonite Negative Fossil Jurassic UK Genuine 30-70mm Specimen with Certificate of Authenticity

Yorkshire Ammonite Negative Fossil – Jurassic, Yorkshire, UK

This genuine Yorkshire Ammonite Negative Fossil is a carefully selected Jurassic specimen from the world-famous fossil-bearing strata of the Yorkshire coast, United Kingdom. Measuring approximately 30–70mm (full sizing please see photo), this piece displays the natural negative impression of an ammonite shell preserved in ancient marine sediment. The photograph provided shows an example of the actual specimen you will receive, ensuring confidence and transparency in your purchase. Every fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming its genuine geological origin.

Geological Age and Formation

This fossil originates from the Jurassic Period, approximately 201–145 million years ago, when much of what is now the UK was submerged beneath warm, shallow seas. The Yorkshire coastline, particularly around Whitby and the Cleveland Basin, is internationally renowned for its Lower and Middle Jurassic marine deposits. These sedimentary rocks, formed in calm offshore environments, consist primarily of shale, mudstone, and limestone that once accumulated on the seabed.

During the Jurassic, ammonites thrived in these nutrient-rich waters. Upon death, their aragonitic shells settled onto the seabed, where they were rapidly buried by fine sediments. Over millions of years, compaction and mineralisation preserved the shell structure or, in cases such as this specimen, left behind a detailed negative mould after the original shell dissolved.

Fossil Type – Negative Ammonite Impression

A negative ammonite fossil represents the external mould left behind when the original shell material has dissolved away, leaving a crisp imprint within the surrounding rock matrix. These natural impressions beautifully capture the spiral geometry and ribbing pattern characteristic of ammonites.

The preserved whorl structure often reveals:

• Planispiral coiling

• Ribbed ornamentation along the shell surface

• Chamber divisions that once housed the buoyancy-regulating gas-filled compartments

The absence of the shell itself highlights the fine sedimentary detail and provides a striking natural contrast between fossil and matrix. Each specimen is unique, reflecting the natural fossilisation process.

About Ammonites

Ammonites belong to the Class Cephalopoda, Order Ammonitida, an extinct group of marine molluscs closely related to modern squid, cuttlefish, and octopus. Unlike their modern relatives, ammonites possessed an external coiled shell divided internally by septa into chambers. These chambers were connected by a siphuncle tube, allowing the animal to regulate buoyancy as it moved through the water column.

Ammonites were fast-evolving and geographically widespread, making them excellent index fossils for dating Jurassic rock layers. Their distinctive ribbing, coiling, and suture patterns vary between species and geological stages, which is why Yorkshire ammonites are highly sought after by collectors and geology enthusiasts worldwide.

Depositional Environment

The Yorkshire Jurassic seas were shallow epicontinental marine environments with periodic low-oxygen conditions that enhanced fossil preservation. Fine-grained muds gently blanketed the seabed, capturing delicate impressions before significant decay or disturbance could occur. These stable sedimentary conditions are responsible for the exceptional detail preserved in many Yorkshire ammonite moulds.

Authenticity and Presentation

This fossil is a genuine specimen sourced from Yorkshire, UK. It has been carefully chosen for quality and visual appeal. The image provided shows an example of the actual piece you will receive. Size range: 30–70mm (please refer to photo for precise scale).

Each fossil includes a Certificate of Authenticity lifetime guarantee generic card, offering assurance of its natural origin and geological age.

A classic piece of British Jurassic history, this Yorkshire Ammonite Negative Fossil is ideal for fossil collectors, geology students, educational displays, or as a unique natural history gift.