Arnioceras semicostatum Ammonite Fossil | Toarcian, Jurassic | Holderness Yorkshire UK | Alice Purnell Collection | Genuine with Certificate

Description

Fossil Type & Species:

This listing features a genuine ammonite fossil of Arnioceras semicostatum, a distinct and scientifically important ammonite species from the Toarcian Stage of the Lower Jurassic Period. Collected from the coastal exposures of Holderness, Yorkshire, United Kingdom, this specimen comes from the highly respected Alice Purnell Collection, which contains expertly curated British fossils with well-documented provenance.

Geological Formation & Insight:

Arnioceras semicostatum is a prominent member of the Psiloceratidae or closely related early ammonite families, and is known for its broad, slightly involute shell with distinctive ribbing — often becoming smoother toward the inner whorls. It is considered an important biostratigraphic index fossil for the Early Jurassic.

This fossil was preserved in marine sediments from the Toarcian Stage, dating to approximately 183–180 million years ago. These layers form part of the Lower Lias succession in the Yorkshire Basin, where deposition occurred in a relatively deep, calm marine setting with periodic anoxic conditions — ideal for fossil preservation.

The Holderness Coast is less well-known than Whitby or Robin Hood’s Bay, but it offers a range of high-quality Jurassic marine fossils, including ammonites that are often exceptionally preserved in grey shales or nodular limestone.

Item Specifics:

• Fossil Type: Ammonite
• Species: Arnioceras semicostatum
• Geological Age: Toarcian Stage, Lower Jurassic (~183–180 million years ago)
• Formation: Lower Lias (Jurassic marine claystone/shale)
• Locality: Holderness, Yorkshire, United Kingdom
• Provenance: From the Alice Purnell Collection
• Preservation: Excellent – detailed ribbing, whorl structure, and natural matrix
• Colour: Natural grey-brown tones in matrix
• Size: See photo — scale rule/cube = 1cm
• Condition: 100% natural with no restoration
• Specimen: You will receive the exact fossil shown in the photographs

Authenticity Guarantee:

All of our Fossils are 100% Genuine Specimens & come with a Certificate of Authenticity. This Arnioceras semicostatum specimen comes from the professionally curated Alice Purnell Collection, ensuring both quality and traceable provenance.

Shipping & Packaging:

Your specimen will be securely packaged and dispatched with full tracking. A wonderful addition for fossil collectors, educators, natural history enthusiasts, or as a unique gift from deep time.

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