Orthocone Nautiloid
Orthoceras cf. regulare • Body fossil / Invertebrate Cephalopod
Geological Period
Devonian - Silurian
Estimated Age
360 to 420 million years
Preservation Type
Mineral replacement (calcite and hematite/bituminous mineralization)
Condition Assessment
Good (Commercially prepared). The specimen has been heavily polished, which enhances aesthetic appeal but removes original surface texture of the phragmocone.
Taxonomic Classification
Phylum: Mollusca, Class: Cephalopoda, Subclass: Nautiloidea, Order: Orthocerida, Family: Orthoceratidae, Genus: Orthoceras (sensu lato)
Morphological Description
Straight (orthoconic) conical shell with visible internal longitudinal structures. Features longitudinal septa and a central siphuncle. The specimen has been polished to reveal the internal chambers and dark mineralization of the shell walls.
Rock Matrix
Black bituminous limestone (often commercially referred to as 'Negro Marquina' style limestone when polished)
Formation & Location
Anti-Atlas Mountains, Morocco (Alnif or Erfoud region)
Size & Dimensions
Approximately 12-15 cm in length; typical for common commercial Moroccan nautiloid specimens.
Value & Rarity
Estimated Market Value
$25 - $50 USD
Auction Estimate
$30 - $60 USD
Rarity Assessment
Common; high volume of these specimens are commercially exported from Moroccan fossil beds.
Scientific Significance
Illustrates the evolution of early cephalopods and the abundance of pelagic life in the Rheic Ocean. These were apex predators of their time, using gas-filled chambers for buoyancy.
Preparation Recommendations
No further preparation required; keep dry and away from acidic cleaners which will etch the limestone matrix. Dust with a microfiber cloth.
Notable Features
High-contrast dark mineralization against the internal calcitic filling. Visible internal siphuncle tube running down the center.