A Trace Fossil on a Silurian Bivalve: Evidence of Predatory Boring?

A Silurian bivalve steinkern, collected from northwestern Ohio, USA, preserves a trace indicative of parasitic or predatory attack. More than 200 steinkerns of Megalomoidea Cox, were visually inspected for evidence of biotic interaction. Of these specimens, one steinkern preserves a trace fossil, as a single, small cylindrical protrusion on its surface. After reconstructing the bivalve shell, the trace fossil is shown to represent a cylindrical hole, of sufficient depth to have penetrated the shell. Preserved morphological characters allow assignment of this trace to Oichnus simplex Bromley. The trace represents either predation or parasitism on this epifaunal bivalve. While evidence of shell boring is common among post Paleozoic bivalves, this example represents one of only a handful of cases found in older bivalves. Undoubtedly, there are evolutionary explanations for this pattern, but the low frequency of preserved Paleozoic aragonitic shells indicates that preservational biases may play an important role. The trace reported here marks the first documented evidence of Silurian bivalve shell boring from North American strata.