Sirenian Rib Bone Fragment (Sea Cow)
Metaxytherium floridanum cf. • Body fossil; Vertebrate skeletal remains
Geological Period
Miocene to Pliocene
Estimated Age
2 to 23 million years
Preservation Type
Permineralization (specifically permineralized and heavily mineralized with dark phosphates characteristic of Florida river fossils)
Condition Assessment
Fair to Good. It is a partial skeletal element with significant river-wear (abrasion) and fractured ends, but the mineral density is excellent.
Taxonomic Classification
Phylum: Chordata, Class: Mammalia, Order: Sirenia, Family: Dugongidae
Morphological Description
Dense, heavy bone fragment showing a characteristic lack of a marrow cavity (pachyostosis). The cross-section reveals an extremely compact, marble-like internal bone structure with fine vascular pitting visible on the weathered surface. It is banana-shaped in curvature with rounded edges due to river tumbling.
Rock Matrix
No original matrix remains; the specimen has been weathered out of the phosphate-rich Hawthorne Group into river gravel. Surface shows minor quartz sand adherence.
Formation & Location
Hawthorn Group (Peace River Formation / Bone Valley Member), Peace River, Arcadia, Florida, USA
Size & Dimensions
Approximately 4 to 5 inches in length. This is a partial fragment of a full rib bone which can reach over 12 inches.
Value & Rarity
Estimated Market Value
$10.00 - $25.00 USD
Auction Estimate
$15.00 - $40.00 USD
Rarity Assessment
Common. Sirenian rib fragments are among the most frequently found vertebrate fossils in the Peace River gravel beds.
Scientific Significance
Illustrates the specialized bone density (pachyostosis) required for buoyancy control in aquatic mammals. Provides data on Miocene/Pliocene marine megafauna distribution in the Southeastern United States.
Preparation Recommendations
Desalination in distilled water if recently recovered; consolidate with a light coating of Paraloid B-72 if flaking; display in a dry environment.
Notable Features
The specimen exhibits extreme pachyostosis, making it significantly heavier than terrestrial mammal bones of similar size. The dark chocolate coloration is diagnostic of phosphate replacement in the Florida fossil record.
Notes
Arcadia Florida peace river