From life to fossil: horseshoe crabs and the preservation of their fluorescence
Mentor 1
Victoria Mccoy
Start Date
14-6-2021 2:15 PM
Description
The ability to fluoresce is found in all modern chelicerates, yet its significance and mechanisms still remain a mystery. Understanding which extinct relatives of these chelicerates were also fluorescent may help solve these mysteries. The ~309 Ma Mazon Creek fossil site provides a rare example of fossil horseshoe crabs that still fluoresce today. The fossils at this site are preserved inside iron carbonate concretions, which are known to be an exceptional host for biomolecule preservation, suggesting that these fluorescent fossils may preserve original biological fluorophores. When studying the preservation of the fluorescence in these fossils, we must ask: was the original biological fluorescence preserved and retained over 309 million years? Or did they lose their biological fluorescence through decay, and then become fluorescent again through some inorganic process during diagenesis and fossilization? Methods to determine original fluorescence or lack thereof, includes chemical analysis, mineralogy, and ultrastructural analysis; this study focused on ultrastructural analysis. One fluorescent horseshoe crab fossil and one non-fluorescent horseshoe crab fossil were thin sectioned; if fluorescence is original, we expect to be able to identify the layered cuticle structure that holds the fluorescence in living horseshoe crabs. We found that the fluorescence is limited to a thin covering on the surface of the fossil, which contains two internal layers. In living horseshoe crabs, the fluorescence is also limited to a thin outer layer of the cuticle (the hyaline layer) which contains two internal layers. Therefore, these results are consistent with original biological fluorescence. However, we also cannot rule out the precipitation of an ~ 0.0025 mm thick layer of fluorescent minerals. In order to assess this, the next step in our research is to quantify the fluorescence. Do the fossils fluoresce as expected for living horseshoe crabs when exposed to the same wavelengths of light?
From life to fossil: horseshoe crabs and the preservation of their fluorescence
The ability to fluoresce is found in all modern chelicerates, yet its significance and mechanisms still remain a mystery. Understanding which extinct relatives of these chelicerates were also fluorescent may help solve these mysteries. The ~309 Ma Mazon Creek fossil site provides a rare example of fossil horseshoe crabs that still fluoresce today. The fossils at this site are preserved inside iron carbonate concretions, which are known to be an exceptional host for biomolecule preservation, suggesting that these fluorescent fossils may preserve original biological fluorophores. When studying the preservation of the fluorescence in these fossils, we must ask: was the original biological fluorescence preserved and retained over 309 million years? Or did they lose their biological fluorescence through decay, and then become fluorescent again through some inorganic process during diagenesis and fossilization? Methods to determine original fluorescence or lack thereof, includes chemical analysis, mineralogy, and ultrastructural analysis; this study focused on ultrastructural analysis. One fluorescent horseshoe crab fossil and one non-fluorescent horseshoe crab fossil were thin sectioned; if fluorescence is original, we expect to be able to identify the layered cuticle structure that holds the fluorescence in living horseshoe crabs. We found that the fluorescence is limited to a thin covering on the surface of the fossil, which contains two internal layers. In living horseshoe crabs, the fluorescence is also limited to a thin outer layer of the cuticle (the hyaline layer) which contains two internal layers. Therefore, these results are consistent with original biological fluorescence. However, we also cannot rule out the precipitation of an ~ 0.0025 mm thick layer of fluorescent minerals. In order to assess this, the next step in our research is to quantify the fluorescence. Do the fossils fluoresce as expected for living horseshoe crabs when exposed to the same wavelengths of light?
