VERY RARE Fossil Heteromorph Ammonite Hypoturrilites gravesianus – Lower Cenomanian, Cretaceous – Chinnor, UK – Alice Purnell Collection

Description VERY RARE HETEROMORPH AMMONITE – HYPOTURRILITES GRAVESIANUS Geological Age: Lower Cenomanian, Cretaceous (~100.5–98 million years ago) Location: Chinnor, Oxfordshire, United Kingdom Formation: Chalk Marl Formation From the Alice Purnell Collection Comes with Certificate of Authenticity This exceptionally rare specimen is a heteromorph ammonite, Hypoturrilites gravesianus, collected from Lower Cenomanian strata in the chalk marl exposures near Chinnor, Oxfordshire. The species is known for its highly unusual shell form and restricted stratigraphic occurrence, making it a prized addition for collectors and institutions alike. Unlike the typical planispiral coiled ammonites, Hypoturrilites species show a loosely coiled, helical shell, often resembling a stretched corkscrew. These highly unorthodox shapes reflect the evolutionary experimentation that ammonites underwent during the mid-Cretaceous period. GEOLOGICAL & TAXONOMIC DETAILS: Species: Hypoturrilites gravesianus Age: Lower Cenomanian (Early Late Cretaceous) Location: Chinnor, UK Formation: Chalk Marl Formation Depositional Environment: Shallow marine carbonate shelf transitioning to open sea marl and chalk deposits Rich in marine invertebrate fossils including ammonites, belemnites, and bivalves Order: Ammonitida Superfamily: Turrilitoidea Family: Turrilitidae Morphology Features: High-spired, helically coiled shell with distinct ribbing Irregular ornamentation with tubercles and fine ribbing in mature specimens Presumed to have had a planktonic or passive-floating mode of life Biozone: Often placed within the Mantelliceras mantelli Zone of the lower Cenomanian Scientific History: First described by D’Orbigny (1850s) and later revised under the genus Hypoturrilites A taxonomically significant genus illustrating transitional forms in ammonite evolution FEATURES & AUTHENTICITY: This fossil has been hand-selected from the Alice Purnell Collection, known for its meticulous documentation and high-grade specimens. The item shown in the photograph is the exact piece you will receive, with a 1cm scale cube included for accurate sizing. The specimen retains excellent preservation of form and surface detail, offering scientific and aesthetic appeal. INCLUDED WITH PURCHASE: Fossil: Hypoturrilites gravesianus Location: Chinnor, Oxfordshire, UK Certificate of Authenticity Precise fossil shown in the listing photo Carefully packed and fully insured shipping Scale cube for size reference (1cm per square) SUMMARY: A museum-quality, heteromorph ammonite fossil, Hypoturrilites gravesianus is rarely encountered on the market. This Lower Cenomanian specimen from Chinnor, UK represents an important piece in mid-Cretaceous paleontology and ammonite evolutionary history. Perfect for collectors, educational use, or as a scientifically significant display piece.