RARE Fossil Ammonite Macrocephalites terebratus – Callovian, Jurassic – Kellaways Sands, Wiltshire, UK – Alice Purnell Collection

Description

RARE FOSSIL AMMONITE – Macrocephalites terebratus

Kellaways Sands | Callovian Stage | Jurassic Period

WILTSHIRE, UNITED KINGDOM

This is a scientifically significant and rarely offered specimen of the large planispiral ammonite species Macrocephalites terebratus, collected from the Kellaways Sands Formation of Wiltshire, UK, dating to the Callovian Stage of the Middle Jurassic, approximately 165 to 161 million years ago.

The specimen comes from the esteemed Alice Purnell Collection and includes a Certificate of Authenticity. The actual specimen in the photo is the item you will receive, with a 1cm scale cube shown for sizing — see images for detailed measurements and condition.

GEOLOGICAL & TAXONOMIC INFORMATION:

• Species: Macrocephalites terebratus
• Geological Period: Jurassic
• Stage: Callovian (Middle Jurassic, ~165–161 Ma)
• Formation: Kellaways Sands Formation
• Location Found: Wiltshire, United Kingdom
• Depositional Environment: Shallow marine, siliciclastic offshore to marginal shelf sands
• Biozone: Typically associated with the Macrocephalites Subzone of the Bullatimorphites bullatus Zone (Callovian)
• Order: Ammonitida
• Superfamily: Stephanoceratoidea
• Family: Macrocephalitidae
• Class: Cephalopoda
• Phylum: Mollusca

MORPHOLOGY & FEATURES:

Macrocephalites terebratus is a highly distinctive ammonite known for its:

• Large, involute shell with a moderately wide umbilicus
• Finely ribbed shell with prominent, often bifurcating ribs crossing the flanks and ventral area
• Slight keel along the venter in mature individuals
• Size variability but often robust in adult form, indicating high palaeoecological plasticity
• Diagnostic of mid-Callovian strata, making it a useful index fossil in European Jurassic biostratigraphy

PALEONTOLOGICAL & GEOLOGICAL CONTEXT:

This species is an important faunal marker in the Kellaways Beds, which reflect a shift from the deeper marine Oxford Clay into more sandy shelf environments. These ammonites are typically preserved in sandy, glauconitic deposits. Their preservation quality, such as seen here, is often excellent due to the mineral-rich depositional environment.

The Macrocephalites terebratus was first formally described in the 19th century and has been used in biostratigraphic frameworks for regional correlation in southern and central England.

SUMMARY OF SPECIMEN:

• Species: Macrocephalites terebratus
• Age: Callovian Stage, Middle Jurassic (~165–161 Ma)
• Geological Unit: Kellaways Sands Formation
• Locality: Wiltshire, United Kingdom
• Preservation: Fine detail, with visible ribs and whorl structure
• Authenticity: Supplied with Certificate of Authenticity
• Collection: Alice Purnell
• Scale Reference: 1cm cube shown in photo for accurate sizing

This Macrocephalites terebratus is a top-quality, rare addition to any collector’s cabinet. Sourced from one of the UK’s classic Jurassic localities and preserved with exceptional care, it offers both scientific and aesthetic value.