Wooster’s Fossils of the Week: Giant Pliocene scallop from Virginia with bonus sclerobionts

Yes, the feature “Wooster’s Fossil of the Week” was retired long ago (all entries still available on this blog), but occasionally I will still cover interesting fossils we come across in the lab or field. The title is now a tradition, even if the items don’t appear every week. No good fossils should be left behind.

The beautiful specimen above was kindly donated to the department last week by Wooster Geologist Alan Troup (’96). He found it and several other specimens in the Yorktown Formation (the Pliocene part) along the York River in Virginia. It will be used in our Paleoecology course next year. These fossil scallops are incredibly abundant, and this is an especially nice one with its numerous sclerobionts (hard-substrate-dwelling organisms). The main shell is Chesapecten jeffersonius, one of the largest scallops ever and the state fossil of the Commonwealth of Virginia. (I don’t know if “Commonwealth Fossil” is a thing.) It is encrusted on the outside only by large barnacles. Near the hinge are numerous perforations from clionaid sponges, making the trace fossil Entobia. It makes for a sweet little community.

Here’s a closer view of Entobia. Each hole leads to a tunnel system in the thick scallop shell.

Other scallops in the collection are encrusted by these thin scleractinian corals with radiating septa inside the  corallites.

The arrow points to a predator drill hole (the trace fossil Oichnus) through the scallop shell. It was made by a naticid gastropod.

Alan’s donation also includes oysters like the above. I’m sure you by now see the included trace fossils!

One of the many interesting questions about these sclerobiont-laden scallops is whether they could do their “swimming” while so heavily encrusted on their exteriors. As you can see in this video, modern scallops can swim today with a good load of passengers.


Ward, L.W. and Blackwelder, B.W. 1975. Chesapecten, a new genus of Pectinidae (Mollusca: Bivalvia) from the Miocene and Pliocene of eastern North America. U.S. Geological Survey Professional Paper 861, 24 p.


About Mark Wilson

Mark Wilson is a Professor of Geology at The College of Wooster. He specializes in invertebrate paleontology, carbonate sedimentology, and stratigraphy. He also is an expert on pseudoscience, especially creationism.
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3 Responses to Wooster’s Fossils of the Week: Giant Pliocene scallop from Virginia with bonus sclerobionts

  1. Bill Reinthal says:

    Mark, you should describe, to your readers, your photographic set-up, to achieve such nice images of beautifully detailed fossils. I think there’s enough interest, out there, that people would want to know how you achieve these exquisite images.

    I, personally, still use variations on techniques, photographic and otherwise, that we all learned in an ancient class, one that was called something like, “Geologic Methods,” (was that part of Jr. IS, or a separate class?) where we learned many valuable tools, some of which have fallen by the wayside, like film developing/printing (unfortunately) and the horrible Leroy lettering system (fortunately), used with Rapidograph pens.

    Maybe Geologic Methods was a pre-field camp class, another requirement that has, unfortunately, lost its place in connecting young geologists with rocks in the wild? I don’t remember the sequence, only the results!

  2. Mark Wilson says:

    Hello Bill! Thanks for this kind note. I work hard on my images, but still consider myself an amateur photographer. You have an excellent suggestion about writing up my photographic methods in another post. I’ve done methodology posts before (notably on making acetate peels) which become useful for students learning new techniques. They also teach me (through the comments) about new ideas and resources. Look for a macrophotography post soon!

    You brought back such memories of our 20th century Geologic Methods course! It was indeed the Junior Independent Study course, which was replaced in the 1990s with individual tutorials. You and I had the classic Professor Roche experience in that earlier course. Remember rolling our own film into canisters in the dark? We then had to photograph a variety of subjects, develop the film, make the prints with a 1940s enlarger, and then use archival glue to paste the photos onto pages in our theses. I spent many all-nighters in that darkroom, most of them fortunately with Gloria! Professor Roche felt so strongly about classic photography that he arranged for the renovated Scovel to have TWO new darkrooms. (Now one is Meagen’s geochemistry lab and the other Shelley’s tectonics lab.) On top of photography, you’ll also remember our epic plane-table mapping excursions around campus, the results for which we drafted on mylar with, as you mentioned, those Rapidograph pens and Leroy lettering sets. Yes, even though those Geologic Methods themselves are long gone, they set us up well for the coming evolution (revolution, really) of scientific tools and ideas.


  3. Emilio says:

    Great photos, it’s really interesting when high level photography meets science. Thanks

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