A Tale of a Concretion: The Pioneering Bivalve That Hitchhiked Into Fresh Water
I was out in central PA last week and the week before, looking for Devonian fish that were swimming up freshwater creeks, along with anything else that fossilized in those ancient waterways. The matrix is fine-grained silt that preserved details wonderfully and where nothing was trapped either preserved as the muddy bottom of the creek or else no texture at all. Imagine my puzzlement when I started finding rounded, swirly ovate lumps of this shale lying about, and even more puzzlement when I found one with spine-like protrusions. My first inclination was that it was a concretion around a fish skeleton, but my gut told me not to do anything other than stabilize it until I had an expert look at it. Fortunately, the Museum of the Earth at the Paleontological Research Institute was on my itinerary between dusty days of field work. I asked at the prep lab if there was anyone on staff who was familiar with the freshwater Devonian of PA. More luck! Both the interns knew the site where I found...
