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Trilobites are one of the most important invertebrate clades in the Palaeozoic, with significant disparity in morphology and behaviour, the latter including intriguing instances of queueing. Previous studies employed Computational Fluid Dynamics (CFD) to investigate queuing behaviour in the Devonian trilobite Trimerocephalus chopini and found drag reduction effects. Novel calculations that define a ratio between drag force and Apparent Gravity (W), along with the Submerged Froude Number (Fr sub), however, reveal that the obtained drag force was practically negligible in terms of the underwater mobility of trilobites. A trilobite would start to experience difficulty in forward walking only when the relative flow speed was over 42 cm/s, which is inconsistent with the interpreted palaeoenvironment or the predicted moving speed of trilobites. Nevertheless, according to the proposed cantilever model, a trilobite had the …