A newly identified species of 10-million-year-old fossil crab unearthed along Calvert Cliffs now carries the name of a volunteer who spent years combing those same cliffs before his unexpected death in 2023.
Researchers have formally described Pinnotheres prochowniki, a fossil pea crab named in honor of Bill Prochownik, a longtime Calvert Marine Museum paleontology volunteer known within the local fossil-hunting community by the nickname “Robo-Bill” for his relentless work excavating specimens from the cliffs, no matter how difficult the dig. Prochownik grew up in Calvert County and died unexpectedly in 2023 at age 40; the museum posthumously named him its 2023 Volunteer of the Year for his contributions to the paleontology program.
The new species is described in a peer-reviewed study published in the Journal of Crustacean Biology, a collaboration between researchers at the Calvert Marine Museum and Kent State University. The paper, titled “Exceptionally Preserved Pea Crabs (Decapoda, Brachyura, Pinnotheroidea) From the Miocene St. Marys Formation, Eastern USA, Exhibiting Preferential Symbiosis With the Surf Clam Mactrodesma subponderosa,” was authored by Stephen C. Groff, Victor J. Perez, Carrie E. Schweitzer, John R. Nance and Cory C. Deltrove — several of whom worked alongside Prochownik on past excavations at the cliffs.
Pea crabs are tiny crustaceans that spend their lives inside the shells of larger host animals, such as clams and oysters, a lifestyle documented in modern species as well as in the fossil record. The newly named fossils date to roughly 10 million years ago, during the Miocene Epoch, and come from Calvert Cliffs in Calvert County along with a similarly aged deposit along the Potomac River in Virginia. Both locations preserve sediment from the St. Marys Formation, part of the layered cliffside geology along the Chesapeake Bay that has made Calvert Cliffs one of the most significant sources of Miocene marine fossils on the U.S. East Coast.
What sets this find apart is the quality of preservation. Many of the fossil crabs were discovered still sealed inside the shells of their host clam, the extinct surf clam species Mactrodesma subponderosa, having apparently been buried rapidly enough in ancient sediment to preserve not just their exoskeletons but, in some specimens, delicate soft tissue including gills — detail that almost never survives in the fossil record. Because most evidence of ancient species interactions comes from trace fossils, which record behavior rather than preserve the organisms involved, researchers said the direct physical association between crab and clam offers an unusually clear window into how the two animals lived together roughly 10 million years ago, with evidence suggesting the crabs may have lived as parasites exclusively within that one clam species.
Researchers noted a living parallel in the Chesapeake Bay today: the modern oyster crab, Zaops ostreum, lives inside oysters in a similar arrangement and is a close relative of the newly described fossil species. Despite sharing comparable lifestyles, the precise evolutionary relationship between the fossil pea crab and its modern relative remains unresolved, according to the study.
Calvert Cliffs has produced significant fossil finds for well over a century, and the Calvert Marine Museum in Solomons has built much of its identity around the site, housing a collection of roughly 200,000 specimens spanning the region’s paleontology alongside its exhibits on Chesapeake Bay estuarine life and maritime history. Museum paleontology curator Stephen Godfrey has overseen decades of excavation work along the cliffs, and the program relies heavily on a corps of volunteers who help locate, excavate and prepare fossils recovered from the eroding cliffline — work that requires both patience and physical persistence, qualities colleagues said defined Prochownik’s approach to the job. Friends who worked alongside him have said his personal favorite fossil find was any specimen of Ecphora, an extinct marine snail with a long fossil record along the Mid-Atlantic coastal plain and Maryland’s official state fossil shell.
The research article is available through the Journal of Crustacean Biology’s website for those interested in the full technical description of the new species and its geological context.
