Clustered and injured Pseudogygites latimarginatus from the Late Ordovician Lindsay Formation, Canada

Insight into how extinct animals responded to injuries developmental malfunctions and pathologies can be derived by examining malformed specimens. Trilobites are an ideal group for understanding how a completely extinct group of arthropods responded to and recovered from these conditions, as their biomineralised exoskeletons preserves malformations. Here we consider a slab containing eight individuals of the asaphid trilobite Pseudogygites latimarginatus from the Colling-wood Member of the Lindsay Formation, Canada. Examining this slab, two individuals with malfor-mations are documented. These malformations are considered injuries and used to demonstrate how P. latimarginatus recovered from failed predation attacks, allowing us to consider possible predator groups. The cluster is interpreted as possible evidence for an in situ biological aggregation that was preserved prior to a moulting event. Implications for this gregarious behaviour are considered, presenting more insight into the palaeoecology of Ordovician asaphid trilobites.