Ecosystems are characterized by complex interactions among living organisms. The fossil record often masks these relations by its incomplete nature and the common spatial displacement of organisms following their death (i.e., taphonomic barriers). These preservational barriers are mitigated in particular by two ancient life strategies: encrustation and encryption. Both life-styles are favourably preserved because taphonomic dispersion of encrusted skeletons and encrypted trace fossils from their substrates are rare. Here, we present a fossil occurrence from the Silurian Jupiter Formation (Aeronian) on Anticosti Island (Quebec, Canada), that has fortuitously preserved a rare sequence of 4 in-vivo animal interactions preserved on one gastropod conch. A large shell of the gastropod Phanerotrema is encrusted with a specimen of Clathrodictyon. A small hole (1.7 mm in diameter) in the surface of the stromatoporoid near the top of the spire of the shell, most likely penetrates both skeletons. Nestled in situ within the hole is a phosphatic brachiopod, identified as Rowellella. The gastropod and stromatoporoid apparently lived and thrived together, presumably over an extended period of time. The snail then died, leaving a recumbent shell on the seafloor. Within a short time, the stromatoporoid was bored, probably by a sipunculan or polychaete worm, yielding a Trypanites dwelling cavity. This was occupied by the phosphatic brachiopod, which allowed the still-growing Clathrodyction to surround its shell, producing an embedment cavity. This is evident by the lenticular shape of the
dwelling that matches the cross-section of the brachiopod. Eventually, the entire community perished, likely from a storm burial event. Without cutting the sample, it is not clear that the original dwelling of the brachiopod was a Trypanites cavity, but borings of this kind are very common in skeletal material and hardgrounds from Anticosti Island even in shells of Phanerotrema. A dozen specimens of stromatoporoid and coral skeletons also show embedment structures with nestled Rowellella specimens initiated in abandoned Trypanites cavities, which seem to be the preferred substrate of the borer. The interaction with the gastropod shell is therefore perhaps no more than an opportunistic occurrence, but the example broadens our understanding of interactions in fossil marine ecosystems.
2004. 192- p.