RARE Fossil Ammonite Roloboceras hambrovi – Lower Aptian, Cretaceous – St. Oswald’s Bay, Dorset, UK – Alice Purnell Collection

Description

RARE FOSSIL AMMONITE – Roloboceras hambrovi – LOWER APTIAN – CRETACEOUS – ST. OSWALD’S BAY, DORSET, UNITED KINGDOM

This listing features a rare and scientifically notable specimen of the ammonite Roloboceras hambrovi, collected from the Greensand deposits of St. Oswald’s Bay on the Jurassic Coast of Dorset, England. Dating from the Lower Aptian Stage of the Early Cretaceous (approximately 125 to 113 million years ago), this ammonite represents a unique part of Britain’s rich palaeontological record.

The specimen comes from the well-known Alice Purnell Collection and is accompanied by a Certificate of Authenticity, guaranteeing its provenance and legitimacy. The actual fossil shown in the photo is the item you will receive. A scale cube (1cm per square) is included for reference — please view the image for full dimensions.

GEOLOGICAL & TAXONOMIC DETAILS:

• Species: Roloboceras hambrovi
• Geological Period: Cretaceous
• Geological Stage: Lower Aptian (~125–113 Ma)
• Formation: Upper Greensand / Lower Greensand beds
• Location: St. Oswald’s Bay, Dorset, United Kingdom
• Depositional Environment: Shallow marine transgressive system, glauconitic sands indicative of slow sedimentation on an open shelf
• Family: Deshayesitidae (tentative)
• Superfamily: Deshayesoidea
• Order: Ammonitida
• Class: Cephalopoda
• Phylum: Mollusca

MORPHOLOGY & FEATURES:

Roloboceras hambrovi is a relatively uncommon heteromorph or planispiral ammonite known for:

• Involute shell form with moderately compressed whorls
• Well-preserved ribbing across flanks and venter
• Occasional weak tubercles on the umbilical or ventral shoulders
• Typically small- to medium-sized specimens found in UK Greensand exposures
• Complex suture lines in mature specimens, aiding in identification

The presented piece displays excellent preservation of these diagnostic features and likely represents a juvenile to sub-adult growth stage.

BIOSTRATIGRAPHIC & PALEONTOLOGICAL SIGNIFICANCE:

• The genus Roloboceras is significant in the biostratigraphic correlation of Aptian Greensand sequences, particularly in southern England.
• Ammonites from this zone help correlate marine faunal stages across Western Europe.
• Its presence indicates mid-Aptian transgressive marine conditions, making it useful in reconstructing palaeoenvironmental shifts in the Cretaceous Western Tethys margin.

SUMMARY OF SPECIMEN:

• Species: Roloboceras hambrovi
• Age: Lower Aptian, Early Cretaceous (~125–113 Ma)
• Location: St. Oswald’s Bay, Dorset, UK
• Formation: Greensand
• Preservation: Excellent detail with clearly defined ribbing and shell form
• Provenance: Alice Purnell Collection
• Authenticity: Supplied with Certificate of Authenticity
• Scale Reference: 1cm cube included in photo (see listing images)

This rare Roloboceras specimen is a scientifically valuable addition to any palaeontological collection and a stunning natural history piece. Whether for study, display, or investment, it offers both beauty and significance.