Paper No. 25
Presentation Time: 9:00 AM-6:00 PM
PRESERVATION AND PIGMENTATION OF THE MIOCENE GASTROPOD ECPHORA
The genus Ecphora of Muricid gastropods from the mid-Miocene Calvert Cliffs, Maryland are characterized by their distinct coloration that ranges from tan to dark brown to reddish-brown hues. This unusual, and as yet uncharacterized, pigmentation presents an opportunity to study biomineralization and the possible preservation of protein within 8-18 Ma shells. Ecphora in its various species and subspecies spans nearly 10 million years of time along Calvert Cliffs, MD within the Calvert, Choptank, and St. Marys Formations. Mollusc shells predominantly form by a process of biomineralization wherein calcium carbonate precipitates in association with an organic matrix made of proteins and polysaccharides. The coloring of these molluscs is the result of shell-binding proteins associated with pigments within the outer calcite portion of the shell. Micro-Raman spectroscopy indicates the presence of a carotenoid like pigment. To extract the organic material, we dissolved shells in dilute HCL. A sheet-like residue of the same color as the initial shell is concentrated in the solution. C:N elemental and isotopic analysis confirmed that the sheet-like material released from the shells is organic. Total organic carbon in the residue from acid treatment ranges from 4 to 40%, with 11 < C/N < 14. Isotope values for carbon (-17 < δC13 < -15‰) indicate a marine environment, while values for nitrogen (3 < δN15 < 5‰) confirm Ecphora’s role as a predator. The remarkable preservation of this pigmentation and shell-binding organic material presents a unique opportunity to study the ecology of the Chesapeake Bay region 8-18 million years ago.