Computational fluid dynamics confirms drag reduction associated with trilobite queuing behaviour

Queuing behaviour has been documented in marine arthropods from Cambrian to modern oceans. One possible explanation of this behaviour is drag reduction, with trilobites in the following positions hypothesized to produce less drag than those leading. In this study, we evaluate the hydrodynamics of queuing behaviour in the Devonian trilobite Trimerocephalus chopini using computational fluid mechanics. Our results show that the drag forces of the trilobites following in the queue were substantially lower than those produced by the leader (75.1% lower at 2 cm s-1). Drag reduction is positively correlated with the movement speed of the trilobites, but decreases with increasing distance from the leader. Our results support the hypothesis that the queuing behaviour of trilobites was an adaptation for reducing hydrodynamic drag. This drag reduction effect compensated for the energy cost of movement, which would have been particularly advantageous during migration.