Functional morphology of the Cambrian archaeocyath sponge Yukonensis.

Archaeocyatha is a diverse clade of Early to Middle Cambrian (Stage 2-4) reef building filter-feeding sponges. Their calcium carbonate skeletons allowed for a broad range of morphologies, from cylindrical to conical or even domal, representing a key adaptation for filter feeding across a wide range of environmental conditions. Within archaeocyath morphospace, Yukonensis yukonensis is uniquely constructed from multiple stacked, porous, subspherical chambers with prominent bowl-shaped thorny corollas surrounding the base of each chamber. Given its morphological complexity, Yukonensis has been challenging to interpret paleobiologically and integrate with our understanding of archaeocyath ecology as a whole. Here, we use fluid and structural mechanical modelling to provide insight on the biological utility of some of its unique anatomical characters. Our fluid dynamics modelling demonstrates that the thorny corolla substantially alters ambient flow preventing water from entering external tumuli pores that are present on the subspherical chambers. Our fluid-structure interaction analyses show that the unique T-shaped ridges along the thorny corolla spines experience increased stress, implying that their architecture did not increase structural rigidity as previously hypothesized, but must instead have served an alternative function. Taken collectively, the results of our multiphysics modelling provide insight into the paleoecology of one of the most enigmatic Cambrian suspension feeders and a quantitative means of testing the efficacy of biological functions in the oldest animal reef communities.