Orthoceratid Nautiloid Fossil
Orthoceras cf. oelandicum • Body fossil, invertebrate
Geological Period
Ordovician to Permian (likely Silurian or Devonian based on typical matrix and preservation)
Estimated Age
440 to 360 million years
Preservation Type
Permineralization and calcification within a natural mold/cast matrix
Condition Assessment
Fair to Good; the specimen is partially weathered and incomplete, representing a fragment of the phragmocone embedded in matrix with surface abrasion
Taxonomic Classification
Phylum Mollusca, Class Cephalopoda, Subclass Nautiloidea, Order Orthocerida
Morphological Description
Elongated, straight conical shell with clearly visible internal septa dividing the phragmocone into distinct chambers. The sutures are relatively simple and transverse to the long axis of the shell. Surface shows weathering along the longitudinal axis, exposing the internal chamber structure.
Rock Matrix
Buff-colored, weathered argillaceous limestone / micrite matrix with iron oxide staining (limonite/hematite)
Formation & Location
Commonly found in marine limestone formations worldwide, such as the Trenton Group (North America) or the Orthoceratid Limestone of Baltoscandia
Size & Dimensions
Visible shell fragment is approximately 5 to 7 cm in length and 1.5 to 2 cm in width at the wider end
Value & Rarity
Estimated Market Value
$25 to $75
Auction Estimate
$30 to $60
Rarity Assessment
Common
Scientific Significance
Provides evidence of early Paleozoic marine ecosystems and the evolutionary development of early shelled cephalopods
Preparation Recommendations
Mechanical cleaning using a micro-scribe to gently clear matrix from the edges of the shell. Store in a dry environment to prevent further weathering of the limestone matrix
Notable Features
Clear exposure of the internal septal walls and chamber stacking due to natural weathering along the ventral side of the shell