AA Grade Dactylioceras tenuicostatum Ammonite Fossil Whitby Jurassic UK Positive Negative Specimen Authentic Certified

Description

AA Grade Dactylioceras tenuicostatum Fossil Ammonite

This outstanding AA Grade Dactylioceras tenuicostatum Fossil Ammonite, preserved with both positive and negative impressions, originates from the world-famous fossil-bearing cliffs of Whitby, Yorkshire, United Kingdom. Dating to the Middle Lias of the Early Jurassic period, approximately 180 million years ago, this specimen represents one of the most iconic and recognisable ammonite species found in Britain.

The fossil you see in the photographs is the exact specimen you will receive, carefully selected for its exceptional preservation, symmetry, and scientific interest. It is a genuine fossil and includes a Certificate of Authenticity lifetime guarantee card, ensuring confidence in its provenance and quality.

Scientific Classification & Geological Context

Dactylioceras tenuicostatum belongs to the family Dactylioceratidae, within the order Ammonitida and subclass Ammonoidea. This species is particularly significant as it defines the tenuicostatum biozone of the Lower Jurassic (Toarcian stage), making it an important index fossil used by geologists to date sedimentary rock layers with precision.

The Whitby Mudstone Formation, where this fossil was found, represents a marine depositional environment formed in a relatively deep, oxygen-poor sea. Fine-grained sediments allowed for exceptional fossil preservation, often capturing intricate shell details and delicate ribbing.

Morphology & Notable Features

Dactylioceras tenuicostatum is characterised by its evolute shell, meaning the whorls are openly coiled with earlier whorls clearly visible. The species exhibits fine, densely packed ribs (costae) that radiate across the shell, giving it a distinctive textured appearance. These ribs often bifurcate as they extend outward, creating a delicate yet highly structured pattern.

This particular specimen is especially desirable as it includes both the positive (raised ammonite form) and negative (impression in the matrix), offering a complete representation of the fossilisation process. The contrast between the fossil and surrounding matrix enhances its visual appeal and educational value.

Discovery & Professional Preparation

This specimen was discovered by our experienced team members, Alister and Alison, along the Jurassic Coast exposures of Whitby. Following careful extraction, it has been professionally cleaned, prepped, and treated by Alison to stabilise the fossil and reveal its finest details.

The preparation ensures the ammonite’s natural features are clearly visible while preserving the integrity of both the positive and negative impressions. This level of care makes the specimen suitable for both display and study.

Authenticity & Certification

Every fossil we offer is 100% genuine and ethically sourced. This ammonite comes complete with a Certificate of Authenticity lifetime guarantee card, providing assurance for collectors, educators, and enthusiasts alike.

The specimen has been individually selected for quality, meaning you are purchasing a unique piece rather than a generic example. The included photographs show the exact fossil you will receive, allowing full transparency and confidence in your purchase.

Display, Collectability & Educational Value

Whitby ammonites are among the most sought-after fossils in the UK due to their historical significance and exceptional preservation. Dactylioceras tenuicostatum, in particular, is highly valued by collectors for its role as a key index fossil and its classic ribbed morphology.

The inclusion of both positive and negative forms makes this specimen especially desirable, offering a deeper understanding of fossil preservation and sedimentary processes. It is ideal for display in a collection, use in educational settings, or as a distinctive gift for fossil enthusiasts.

Please refer to the photographs for full sizing and detailed condition, as these images represent the exact specimen available.