Explaining gregarious behaviour in Banffia constricta from the Middle Cambrian Burgess Shale,British Columbia

Banffia constricta is an enigmatic Burgess Shale animal originally described by Charles Walcott in 1911 as an annelid, and more recently as a stem‐group deuterostome. Interpreted, on the basis of anatomy, to have been bottom‐feeders, there are few other data from which to draw interpretations of Banffia's life habit. A slab of Burgess Shale with a dense aggregation of B. constricta may indicate a gregarious habit for the animal, as taphonomic and stratigraphical data indicate an in situ origin for the assemblage. Clustering of individuals, high density of the individuals and non‐random within‐cluster orientation support the hypothesis that detritus‐feeding B. constricta congregated to feed on a local, rich food source. Presumed opportunistic feeding aggregations have been documented in at least one other Burgess Shale taxon and have been described for other fossil benthic marine invertebrates. Extant benthic marine invertebrates such as holothurians and echinoids exhibit mass feeding behaviour and may serve as modern analogs for the behaviour represented by the B. constricta assemblage.