Dorsal Fin Spine (Hybodont Shark)
Hybodus cf. montanensis • Body fossil / Vertebrate (Chondrichthyes)
Geological Period
Cretaceous
Estimated Age
66 to 100 million years
Preservation Type
Permineralization with probable phosphate enrichment (Apatite replacement)
Condition Assessment
Fair to Good. The spine appears mostly complete but shows signs of surface weathering and a possible break at the distal tip.
Taxonomic Classification
Phylum: Chordata, Class: Chondrichthyes, Order: Hybodontiformes, Family: Hybodontidae, Genus: Hybodus sp.
Morphological Description
Elongated, slender, tapering bone-like structure. Features longitudinal ribbing/striations along the shaft and a row of small, backward-pointing denticles (tubercles) near the base. The cross-section is laterally compressed.
Rock Matrix
Specimen is missing its original matrix; resting on an unrelated polished granite countertop. Likely originated from a sandy or silty mudstone matrix.
Formation & Location
Commonly found in the Hell Creek Formation (USA) or Kem Kem Beds (Morocco).
Size & Dimensions
Approximately 5-8 cm in length, which is consistent with a juvenile or smaller species of hybodont shark.
Value & Rarity
Estimated Market Value
$25 - $60 USD
Auction Estimate
$40 - $80 USD
Rarity Assessment
Uncommon. While isolated teeth are common, well-preserved fin spines are less frequently recovered in one piece.
Scientific Significance
Fin spines help paleontologists track the evolution of primitive sharks and define paleo-environments, as hybodonts occupied both marine and freshwater niches.
Preparation Recommendations
Keep in a low-humidity environment to prevent pyrite disease if present. Clean with a dry soft brush; avoid water or acids.
Notable Features
Distinctive posterior denticles used for defense and anchoring the dorsal fin; the reddish-brown coloration suggests high iron content in the original fossilization environment.