Orthocone Nautiloid
Orthoceras sp. (commonly referred to in trade; potentially Michelinoceras or Arionoceras) • Body fossil; Marine cephalopod (Invertebrate)
Geological Period
Devonian (possibly Silurian to Carboniferous)
Estimated Age
360 - 420 million years
Preservation Type
Recrystallization; original aragonite replaced by black calcite/limestone and white sparry calcite filling the internal chambers.
Condition Assessment
Good; professionally polished to reveal internal anatomy, though it is a partial section of a larger shell. Some distal breakage is noted.
Taxonomic Classification
Phylum: Mollusca, Class: Cephalopoda, Subclass: Nautiloidea, Order: Orthocerida, Family: Orthoceratidae
Morphological Description
Elongated, slender conical shell (phragmocone) showing distinct septal chambers. The specimen is a longitudinal cross-section revealing the internal camerae and a centralized siphuncle tube. The tapering indicates the growth direction towards the living chamber.
Rock Matrix
Black bituminous limestone matrix characteristic of the Anti-Atlas mountain localities.
Formation & Location
Commonly found in the Erfoud region of the Anti-Atlas Mountains, Morocco; specifically within the Tafilalt or Ma'der basins.
Size & Dimensions
Approximately 12-15 cm in length; typical for common commercial specimens.
Value & Rarity
Estimated Market Value
$15 - $40 USD
Auction Estimate
$20 - $50 USD
Rarity Assessment
Common; high volume of extraction and commercial preparation from Moroccan deposits.
Scientific Significance
Provides evidence of Paleozoic pelagic marine ecosystems and the evolution of cephalopod buoyancy control via siphuncular systems.
Preparation Recommendations
Specimen is already polished; maintain in dry conditions. No acidic cleaners should be used as it is composed of calcium carbonate.
Notable Features
High contrast between the black matrix and white calcite chamber infilling. Excellent visibility of the septa and longitudinal symmetry.