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The Raft of the Medusa

October 28, 2014

There is really no way of knowing what the media, scientific or otherwise, will grab onto.

A week ago, at the Geological Society of America meeting in Vancouver, I presented a descriptive talk that may well have been the simplest I had ever given to a scientific audience. We had just listened to a series of presentations, many of them by students and postdocs, which incorporated considerable amounts of “big science”: sophisticated imaging techniques, chemical analyses of fossil preservation, or multivariate statistical studies of large numbers of specimens.

When I got up in front of the same audience, I was a bit worried because I realized that my talk could have been just as easily presented in 1914 as 2014: I was describing a single specimen, illustrated with photographs. Nineteenth century Natural History, really. But it was such a strange specimen that it seemed worth presenting, and as it turned out, the reporter from Science News thought so too (here is his short article, freshly out).

Carboniferous (Pennsylvanian) fossil jellyfish from the Mecca Shale (Field Museum of Natural History, PE23963)

Carboniferous (Pennsylvanian) fossil jellyfish from the Mecca Shale (Field Museum of Natural History, PE23963)

Those of you who visit this page occasionally will know that I am, perhaps, obsessed with the topic of jellyfish fossilization. In addition to ongoing detailed work on Ordovician-age jellies from the William Lake site in Manitoba, I have been collaborating with my colleague James Hagadorn of the Denver Museum to figure out the global fossil record of medusae.

Jellyfish are rarely fossilized; many things have been published as fossil jellies, but few of those actually are preserved medusae. So we have been working through the world literature of all papers published describing “fossil jellyfish.” As we have studied the literature, James and I have determined which museums hold collections that need to be examined, and when the opportunity arises we will go and spend a day or two on a collections visit. When necessary, we will borrow material for further study: some of the fossils are easily interpreted, but others are problematic.

The presentation in Vancouver was about one of the specimens we had found in the huge collections of the Field Museum in Chicago. Preserved in a slab of the Carboniferous Mecca Shale from Indiana, it looked like a blob of pure white quartz sand surrounded by thinly bedded black shale. Except this was a sand blob with tentacles.

Paleontological collections storage at the Field Museum

Paleontological collections storage at the Field Museum

Spending many days with the specimen, photographing it in every possible way (double polarized photography is our friend!), we were able to recognize many features that allowed us to identify it as a chirodropid cubozoan (a group of box jellyfish still abundant in modern oceans). It is the same age as the box jellies in the well-known Mazon Creek Lagerstätte of Illinois, and it is very similar to the Mazon Creek box jelly Anthracomedusa turnbulli, but preserved in a very different way. We explained its unusual preservation in this manner: A body of pure quartz sand is very unusual in the middle of a black shale bed; this resulted from sediment rafting by the jellyfish, a process analogous to ice rafting. The medusa apparently stranded on a beach, ingested sand as it attempted to free itself, and then was washed or rafted into a lagoon where it was buried in anoxic mud.

The scientific manuscript describing this remarkable fossil is almost complete. Maybe this publicity will motivate me to get it out the door and move on to the next batch of “fossil jellyfish”!

© Graham Young, 2014

5 Comments leave one →
  1. Steve Brandy permalink
    October 29, 2014 7:33 am

    Hi Graham. The instant I saw this fossil, I knew it was a jellyfish…it brings to mind a Portuguese Man’O War. I understand as well, that the “softer bodied” creatures were not usually good candidates for fossilization, making this example rarer than other fossils from the same time period. I’m still looking forward to seeing some of the fossils from your Churchill River gatherings.

    Much peace

    • Graham permalink*
      October 29, 2014 9:32 pm

      Thanks Steve. I am working on those Churchill River posts!

  2. Steve Brandy permalink
    November 18, 2014 9:34 am

    I had to add another comment Graham. Inadvertently, you educate me more about zoology than paleontology. Although the “medusa” fossil you feature, looks like a Portuguese Man O’ War, I learn now that the Man O’ War is really classified as a siphonophore and a colony of zooids that are mutually dependent. It is not as I thought….a jellyfish Having mentioned that…. the fossil still looks more like a Man O’ War than a jellyfish…It may have been distorted along its pathway to fossilization, giving it the appearance of a Man O’ War. It’s a nasty beast, or, shall I say, a nasty collection of beasts, with powerful toxins to sting one and, a siphon that is pressurized with some percentage of …carbon monoxide! Very interesting indeed. Could this fossil be one? If the Man O’ War existed at that time….?

    • Graham permalink*
      November 25, 2014 10:41 pm

      Hi Steve, we have considered various possibilities, and the fossil is clearly a box jellyfish – we will finish the paper about it when we have time! Portuguese Man O’War don’t really have a fossil record, but of course there is hope that we will find some at some point.

  3. November 30, 2014 5:08 pm

    Graham: I have two photos of a possible Silurian ‘jellyfish’ I’d like to send to you. How do I do that?
    Sam (Sam Ciurca, Rochester, New York)

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