Fossil Ammonite Arnioceras kridioides Upper Sinemurian Jurassic Robinhoods Bay UK

Description

Fossil Ammonite – Arnioceras kridioides

This listing features a genuine fossil ammonite of Arnioceras kridioides, dating from the Upper Sinemurian stage of the Early Jurassic (around 195 million years ago). Sourced from the world-renowned exposures at Robin Hood’s Bay, Yorkshire, United Kingdom, this ammonite is a carefully selected specimen. The photographs provided show the exact fossil you will receive, with a 1 cm scale cube included for accurate sizing. Each specimen is supplied with a Certificate of Authenticity, guaranteeing that it is a 100% genuine fossil.

Geological Context

The Upper Sinemurian represents a key interval within the Early Jurassic, characterised by dynamic shallow marine ecosystems and a rich diversity of ammonite faunas. Robin Hood’s Bay in North Yorkshire is one of Britain’s most celebrated Jurassic fossil localities, with exposures of the Lower Lias Group, including finely bedded shales and limestones. These rocks were deposited in calm, shallow marine conditions, allowing for exceptional preservation of ammonites and other marine life. The biozones of the Sinemurian, particularly the upper intervals, are defined in part by ammonites such as Arnioceras, making them critical for stratigraphic studies.

Scientific Classification

• Kingdom: Animalia
• Phylum: Mollusca
• Class: Cephalopoda
• Order: Ammonitida
• Superfamily: Psiloceratoidea
• Family: Arietitidae
• Genus: Arnioceras
• Species: Arnioceras kridioides

Morphological Features

Arnioceras kridioides displays an evolute shell with whorls that are relatively compressed and adorned with strong, radiating ribs. These ribs extend from the umbilicus to the venter, creating a bold ribbed pattern typical of the genus. The venter is rounded and often accentuated by the termination of ribs, giving the shell a distinctive appearance. The overall form suggests adaptations for an active, free-swimming lifestyle in the open seas of the Early Jurassic.

Paleoenvironment and Ecology

During the Upper Sinemurian, much of what is now Yorkshire was covered by a warm, shallow epicontinental sea. Ammonites such as A. kridioides thrived as nektonic predators, feeding on smaller marine organisms including crustaceans and molluscs. Their ribbed shells provided structural reinforcement and possibly hydrodynamic advantages. The depositional environment of Robin Hood’s Bay was ideal for fossil preservation, with fine sediments burying ammonites quickly after death, protecting their shells from destruction.

Significance and Collectability

Ammonites of the genus Arnioceras are highly significant in biostratigraphy, as their rapid evolutionary turnover allows geologists to identify and correlate rock layers with great precision. This makes specimens like A. kridioides not only beautiful display pieces but also important scientific tools. Fossils from Robin Hood’s Bay are particularly sought after due to the site’s historical importance and the quality of preservation found there.

Provenance and Authenticity

This specimen was collected in Robin Hood’s Bay, Yorkshire, one of the UK’s most iconic Jurassic fossil sites. It has been cleaned and prepared to highlight its diagnostic features, making it an excellent addition to any collection. As with all of our fossils, it is sold with a Certificate of Authenticity to ensure provenance and guarantee its genuine nature.

A Rare Opportunity for Collectors

Owning an Upper Sinemurian ammonite from Robin Hood’s Bay is a chance to add a scientifically important and visually striking fossil to your collection. Whether you are a keen fossil enthusiast, an academic collector, or someone seeking a unique natural history display piece, this specimen of Arnioceras kridioides is a timeless representation of Britain’s Jurassic heritage.