Ammonite (Douvilleiceras)
Douvilleiceras mammillatum (cf.) • Body fossil; Invertebrate (Cephalopod)
Geological Period
Lower Cretaceous (Albian stage)
Estimated Age
110 to 115 million years
Preservation Type
Recrystallized shell replacement or internal mold with high-fidelity surface detail; likely calcitic or phosphatic permineralization.
Condition Assessment
Very Good to Excellent. The center (umbilicus) is exceptionally well-preserved and clean, with no significant breakage to the outer ribs or calcification obscuring the tubercles.
Taxonomic Classification
Phylum: Mollusca, Class: Cephalopoda, Order: Ammonitida, Family: Douvilleiceratidae, Genus: Douvilleiceras
Morphological Description
Evolutionary planispiral shell with a wide, open umbilicus. Notable for its 'cactiform' appearance, featuring prominent, heavy primary ribs decorated with rows of distinct tubercles (knobs). The ribs are thick and radial, creating a coarse, rugged surface texture typical of the genus.
Rock Matrix
Specimen is mostly free of matrix (prepared), but likely originated from a glauconitic sandstone or grey marly limestone commonly associated with this genus.
Formation & Location
Commonly found in the Gault Clay or Lower Greensand of England/France, or the Mahajanga Basin in Madagascar.
Size & Dimensions
Approximately 8 cm to 12 cm in diameter, fitting within the mid-to-large size range for well-preserved commercial Douvilleiceras specimens.
Value & Rarity
Estimated Market Value
$150 - $450 USD
Auction Estimate
$200 - $600 USD (depending on size and provenance)
Rarity Assessment
Uncommon. While ammonites are generally common, specimens of Douvilleiceras with this level of 3D relief and lack of crushing are more locally restricted.
Scientific Significance
Ammonites are vital index fossils for biostratigraphy. Douvilleiceras represents a successful lineage of Cretaceous predators and provides insight into the marine biodiversity during the Aptian-Albian transition.
Preparation Recommendations
Requires no further mechanical prep. Should be kept in a stable humidity environment away from acidic fumes; display on a soft-padded cradle or acrylic stand to prevent chipping of the tubercles.
Notable Features
The specimen exhibits a high degree of symmetrical tuberosity. The transition from the inner whorls to the outer body chamber shows perfectly graduated growth increments without noticeable pathology.