Computational fluid dynamics confirms drag reduction associated with trilobite queuing behaviour

Abstract

Queuing behaviour has been documented in marine arthropods from Cambrian to modern oceans. It was previously hypothesized that this behaviour provided energy savings through hydrodynamic drafting, with trilobites in 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 dynamics. The results show that the drag forces of the trilobites following in the queue were substantially lower than those produced by the leader (˜65–79% lower at velocities of 0.5–2 cm s−1). Drag reduction was positively correlated with the movement speed of the trilobites, but decreased with increasing distance from the leader, and there was essentially no drag reduction at all for the first following trilobite when the following distance was greater than about six times its body length. This agrees with fossil evidence preserving trilobites in queues in close proximity to each other. The results also show that drag reduction was still significant (˜86.8% at 2 cm s−1) even for the longest queues preserved in the fossil record. Our findings 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.

An earliest Triassic age forTasmaniolimulusand comments on synchrotron tomography of Gondwanan horseshoe crabs

“…Three-dimensional reconstructions are increasingly used in computational fluid dynamics (CFD) to study the hydrodynamic properties of extinct aquatic taxa ( Rahman et al, 2015a ; Darroch et al, 2017 ; Rahman, 2017 ; Gibson et al, 2019 ; Ferrón et al, 2020 ; Hebdon, Ritterbush & Choi, 2020 ; Gibson et al, 2021 ; Song et al, 2021 ). The majority of CFD studies have focused on enigmatic Ediacaran taxa ( Rahman et al, 2015a ; Rahman, 2017 ; Gibson et al, 2019 ), echinoderms ( Rahman et al, 2015b ; Rahman et al, 2020 ; Waters et al, 2017 ), ammonoids ( Hebdon, Ritterbush & Choi, 2020 ), and vertebrate groups ( Dec, 2019 ; Troelsen et al, 2019 ; Ferrón et al, 2020 ; Ferrón et al, 2021 ).…”

“…While fossil arthropods have received comparatively less attention than the aforementioned groups ( e.g. , Pates et al, 2021 ; Song et al, 2021 ), CFD studies have modelled lift and drag experienced by modern xiphosurids ( Bicknell & Pates, 2019 ; Davis, Hoover & Miller, 2019 ). Extending CFD studies to fossil xiphosurids will facilitate comparative studies of the hydrodynamic properties of the carapaces of extinct members of the clade, in addition to elucidating the effects of bizarre morphologies, such as the hypertrophied genal spines, on fluid flow.…”

Peer Review #2 of "An earliest Triassic age for Tasmaniolimulus and comments on synchrotron tomography of Gondwanan horseshoe crabs (v0.1)"

“…Three-dimensional reconstructions are increasingly used in computational fluid dynamics (CFD) to study the hydrodynamic properties of extinct aquatic taxa (Rahman et al, 2015a;Darroch et al, 2017;Rahman, 2017;Gibson et al, 2019;Ferrón et al, 2020;Hebdon et al, 2020;Gibson, et al, 2021;Song et al, 2021). The majority of CFD studies have focused on enigmatic Ediacaran taxa (Rahman et al, 2015a;Rahman, 2017;Gibson et al, 2019), echinoderms (Rahman et al, 2015b(Rahman et al, , 2020Waters et al, 2017), ammonoids (Hebdon, et al 2020), andvertebrate groups (Dec, 2019;Troelsen et al, 2019;Ferrón et al, 2020Ferrón et al, , 2021.…”

Peer Review #2 of "An earliest Triassic age for Tasmaniolimulus and comments on synchrotron tomography of Gondwanan horseshoe crabs (v0.2)"

“…The majority of CFD studies have focused on enigmatic Ediacaran taxa (Rahman et al, 2015a;Rahman, 2017;Gibson et al, 2019), echinoderms (Rahman et al, 2015b(Rahman et al, , 2020Waters et al, 2017), ammonoids (Hebdon, et al 2020), andvertebrate groups (Dec, 2019;Troelsen et al, 2019;Ferrón et al, 2020Ferrón et al, , 2021. While fossil arthropods have received comparatively less attention than the aforementioned taxa (e.g., Pates et al, 2021;Song et al, 2021), CFD studies have modelled lift and drag experienced by modern xiphosurids (Bicknell & Pates, 2019;Davis et al, 2019). Extending CFD studies to fossil Manuscript to be reviewed marginal marine environments (Lamsdell, 2016(Lamsdell, , 2021Bicknell & Pates, 2019;Bicknell & Shcherbakov, 2021;Bicknell et al, 2022a); CFD provides the most compelling method for evaluating the likelihood of this hypothesis.…”