From Life to Fossil: Horseshoe Crabs and the Preservation of Their Fluorescence

Autumn Routson, “From Life to Fossil: Horseshoe Crabs and the Preservation of Their Fluorescence”
Mentor: Victoria Mccoy, Geosciences

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?

Synchronous Presentation April 16th at 2:15pm

Microsoft Teams meeting
Join on your computer or mobile app

Click here to join the meeting

Or call in (audio only)
+1 414-253-8850,,655025361#   United States, Milwaukee

Phone Conference ID: 655 025 361#


  1. Hello! My name is Autumn Routson and I’m currently a junior pursuing my BS in Geoscience. I decided to try my hand at a paleontology-based project this year and had so much fun learning about fluorescence. Please feel free to leave any questions, comments, or even some constructive criticism if you have any! Thanks for visiting my page 🙂

  2. Great talk, Autumn! I feel like there has been a lot of “surprising” florescence in the news lately: platypus, some sharks… Are there any commonalities between these organisms? They seem quite different to me — except they all live in water.

    1. From the perspective that these organisms had different origins in their fluorescent evolution, it’s likely that their functions may be very different, but it’s hard to tell! In order to answer this, we would want to look into the function of the fluorescence for these different groups. As far as I know, these organisms all interact within a different part of the marine ecosystem so their fluorescence is likely to have different purposes. Thanks for watching my talk!

  3. Nice job Autumn. Very professionally done! Do you know what the environment of the Francis Creek Shale (I think that was the unit you mentioned) was? Was it a marine or nonmarine environment? Shallow or deep water environment? What was the type of preservation of the fossil, and do you know how it became fossilized to allow preservation of original shell material?

    1. Hi, John sorry for the late reply! I’m actually looking into the depositional environment of the Francis creek shale for a research project in my sedimentology and stratigraphy class. So far what I’ve found is that the shale was most likely deposited in a delta with a fluctuation between fresh and brackish water in a shallow environment. The type of preservation of the fossil is what we’re still trying to determine! We’re currently looking into getting fluorometry data to compare the fluorescence of the living specimens and our fossils to see if they’re close enough where it would support the fluorescence as being original biologic fluorescence. Another step is to get mineralogical data to find out what minerals are in our concretion and their implications for biologic preservation.

  4. I really enjoyed your presentation today and appreciated your organization and explanations. One function of a Q&A period can be to see how well presenters answer unexpected questions or deal with questions that they don’t know how to answer. I think you got a few questions far off-topic and I thought you did a wonderful job in your responses. I also enjoyed learning of the connection between horse-shoe crab blood and the detection of toxins in covid-19 vaccines. Thank-you for the enjoyable presentation.

    1. Thank you so much, Suzanne! I really appreciate that you watched my talk and the encouraging words. In my free time, I hope to learn more about the ecology of horseshoe crabs and see if their fluorescence might have some connection to attracting bacteria!

Leave a Reply

Your email address will not be published. Required fields are marked *