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.

Reference:

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.