Ammonite
Perisphinctes sp. or similar planulate ammonite (cf. Perisphinctes) • Body fossil (internal/external mold and cast), Invertebrate
Geological Period
Jurassic to Early Cretaceous
Estimated Age
140 to 180 million years old
Preservation Type
Recrystallization and internal mold with calcareous replacement. Weathered surface showing eroded rib structure.
Condition Assessment
Fair. Partially eroded surface with missing outer shell layer, moderate weathering, but retaining clear, identifiable whorl structure and ribbing patterns.
Taxonomic Classification
Phylum Mollusca, Class Cephalopoda, Subclass Ammonoidea, Order Ammonitida, Family Perisphinctidae (cf.)
Morphological Description
Planispiral, evolute coiling showing multiple exposed whorls. Prominent coarse ribbing (costae) bifurcating across the outer whorls, characteristic of perisphinctid ammonites. Strong radial ornamentation with a rounded whorl cross-section.
Rock Matrix
Light gray-tan fine-grained limestone / marly limestone matrix filling the camerae.
Formation & Location
Commonly found in Jurassic limestone deposits such as the Oxford Clay/Corallian formations of the UK, Madagascar marine deposits, or European Jurassic strata (e.g., Solnhofen or Swabian Jura).
Size & Dimensions
Approximately 6 - 8 cm in maximum diameter (hand-held scale), representing a mid-sized juvenile or small adult specimen.
Value & Rarity
Estimated Market Value
$15 - $35 USD
Auction Estimate
$20 - $40 USD
Rarity Assessment
Common. Ammonites of this type are widely distributed worldwide in Jurassic marine deposits.
Scientific Significance
Ammonites are key index fossils used in biostratigraphy for precise dating of marine sedimentary layers during the Mesozoic Era. They provide critical data on ancient marine ecosystems and evolutionary radiation.
Preparation Recommendations
No heavy mechanical preparation needed; optional light air-abrasion could highlight rib details. Store in a dry environment and display on a custom acrylic stand.
Notable Features
Well-preserved evolute planispiral geometry showcasing clear primary and secondary bifurcating ribs near the outer margin, demonstrating classic perisphinctid morphology.