Borings in shells are evident throughout the fossil record, and are commonly used as evidence of predation. Modern predatory borings are site-specific, often leaving a circular Oichnus boring —
similar forms are known as early as the Ordovician. Here, drilled holes in Phanerotrema (Gastropoda) from the Silurian Jupiter Formation on Anticosti Island, Québec, are documented.
Holes occur in 4 of 19 specimens (21%), with a total of 12 completed holes (diameter 0.3-3 mm). They are stout and narrowing conically with depth, and multiple borings within the same shell mostly cluster along the selenizone of the conch (67%). The angle of penetration relative to the surface is variable, but two holes cut into the sediment infilling the shell. The borings in Phanerotrema are interpreted as Trypanites dwelling cavities excavated within a sediment-filled shell. Trypanites is common in skeletal material and hardgrounds from Anticosti, where site-specific distributions occur, especially favouring high-profile substrates. Large shells of Phanerotrema likely resisted complete burial, and were exposed longer to the water column and settling larvae of bioeroders. The highly
sculptured selenizone was the preferred target, as it was the highest point on the recumbent conch. The rugosity of the site also may have favoured settling and initiation of boring larvae. Viewed individually, some of the borings could convincingly be interpreted as resulting from predation, but they provide a cautionary example against hasty interpretation.
2003. 6- p.