Swimming and feeding in the Ordovician trilobite Microparia speciosa shed light on the early history of nektonic life habits

Computational Fluid Dynamic simulations (CFD) show that the Ordovician trilobite Microparia speciosa had a high stability in the horizontal plane (parallel to the flow currents), suggesting that it could be very stable in the water column when it was enrolled, for hovering or to get stabilization when the current disturbed the swimming. This indicates a new way to use enrolment in trilobites during the Ordovician radiation, not only for protection against predators or the environment but also as a hydrodynamic tool to maintain stability within the water column. Metachronal propulsion was likely used by Microparia speciosa for swimming and, in a high-viscosity scenario, also for feeding. This is suggesting given that the vortex below Microparia speciosa takes particles directly to the mouth, and taken more particles when the trilobite is orientated in the way of the current (and no countercurrent). This suggests a passive feeding strategy for better energy saving when the trilobite is hovering in water column.