Trilobites in rock enrol: a comment on ‘Developmental and functional controls on enrolment in an ancient, extinct arthropod’ by Esteve and Hughes (2023)

Chipman, Ariel D.; Drage, Harriet B.

doi:10.1098/rspb.2023.1547

Cited by 4 publications

(5 citation statements)

References 15 publications

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“…These comparisons indicate that despite the distant phylogenetic relationships between trilobites (extinct stem-group chelicerates), isopods (extant crustaceans) and millipedes (extant myriapods), these euarthropods share fundamentally similar exoskeletal ventral adaptations that facilitate protective enrollment. These findings evidence a striking case of convergent evolution that is heavily influenced by the mechanical requirements and limitations necessary to achieve complete encapsulations in euarthropods, which have been extensively investigated in terms of their dorsal exoskeletal morphology (e.g., Esteve et al, 2011, 2017, 2018; Chipman and Drage, 2023), but never from the perspective of the ventral anatomy until now. Repeated convergent evolution of the same mechanism in three distantly related euarthropods demonstrates the constraints of achieving complete enrollment with a rigid exoskeleton, and simultaneously the evolutionary advantages that this strategy must confer.…”

Section: Discussionmentioning

confidence: 93%

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Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods

Losso,

Affatato,

Nanglu

et al. 2023

Preprint

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The ability to enroll for protection is an effective defensive strategy that has convergently evolved multiple times in disparate animal groups ranging from euarthropods to mammals. Enrollment is an evolutionary staple of trilobites, and their biomineralized dorsal exoskeleton offers a versatile substrate for the evolution of interlocking devices. However, it is unknown whether trilobites also featured ventral adaptations for enrolment. Here, we report ventral exoskeletal adaptations that facilitate enrollment in exceptionally preserved trilobites from the Upper Ordovician Walcott-Rust Quarry in New York State, USA. Walcott-Rust trilobites reveal the intricate three-dimensional organization of the non-biomineralized ventral anatomy preserved as calcite casts, including the spatial relationship between the articulated sternites (i.e., ventral exoskeletal plates) and the wedge-shaped protopodites. Enrollment in trilobites is achieved by ventrally dipping the anterior margin of the sternites during trunk flexure, facilitated by the presence of flexible membranes, and the close coupling of the wedge-shaped protopodites. Comparisons with the ventral morphology of extant glomerid millipedes and terrestrial isopods reveal similar mechanisms used for enrollment. The wedge-shaped protopodites of trilobites closely resemble the gnathobasic coxa/protopodite of extant horseshoe crabs. We propose that the trilobites’ wedge-shaped protopodite simultaneously facilitates tight enrollment and gnathobasic feeding with the trunk appendages.

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Section: Discussionmentioning

confidence: 93%

“…1). Trilobite evolutionary history throughout the Paleozoic was heavily influenced by their ability to enroll effectively (e.g., Esteve et al, 2013; Suárez and Esteve, 2021; Chipman and Drage, 2023). Early Cambrian species show evidence of complete but imperfect (i.e.…”

Section: Introductionmentioning

confidence: 99%

Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods

Losso,

Affatato,

Nanglu

et al. 2023

Preprint

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show abstract

“…These findings evidence a striking case of convergent evolution that is heavily influenced by the mechanical requirements and limitations necessary to achieve encapsulation in euarthropods, which have been extensively investigated in terms of their dorsal exoskeletal morphology (e.g. [9,[11][12][13]), but never from the perspective of the ventral anatomy until now. Repeated convergent evolution of the same mechanism in three distantly related euarthropods demonstrates the constraints of achieving complete enrolment with a rigid exoskeleton, and simultaneously the evolutionary advantages that this strategy must confer.…”

Section: (A) Sternite Position During Enrolmentmentioning

confidence: 93%

“…Among extinct species, enrolment has been thoroughly documented in trilobites, a diverse group of marine euarthropods typified by the presence of a biomineralized calcitic dorsal exoskeleton (figure 1). Trilobite evolutionary history throughout the Palaeozoic was heavily influenced by their ability to enrol effectively [7][8][9]. Early Cambrian species show evidence of complete but imperfect (i.e.…”

Section: Introductionmentioning

confidence: 99%

Convergent evolution of ventral adaptations for enrolment in trilobites and extant euarthropods

Losso,

Affatato,

Nanglu

et al. 2023

Proc. R. Soc. B.

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The ability to enrol for protection is an effective defensive strategy that has convergently evolved multiple times in disparate animal groups ranging from euarthropods to mammals. Enrolment is a staple habit of trilobites, and their biomineralized dorsal exoskeleton offered a versatile substrate for the evolution of interlocking devices. However, it is unknown whether trilobites also featured ventral adaptations for enrolment. Here, we report ventral exoskeletal adaptations that facilitate enrolment in exceptionally preserved trilobites from the Middle Ordovician Walcott–Rust Quarry in New York State, USA. Walcott–Rust trilobites reveal the intricate three-dimensional organization of the non-biomineralized ventral anatomy preserved as calcite casts, including the spatial relationship between the articulated sternites (i.e. ventral exoskeletal plates) and the wedge-shaped protopodites. Enrolment in trilobites is achieved by ventrally dipping the anterior margin of the sternites during trunk flexure, facilitated by the presence of flexible membranes, and with the close coupling of the wedge-shaped protopodites. Comparisons with the ventral morphology of extant glomerid millipedes and terrestrial isopods reveal similar mechanisms used for enrolment. The wedge-shaped protopodites of trilobites closely resemble the gnathobasic coxa/protopodite of extant horseshoe crabs. We propose that the trilobites' wedge-shaped protopodite simultaneously facilitated tight enrolment and gnathobasic feeding with the trunk appendages.

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“…Genal prolongations in the South American trinucleid Fantasticolithus isabelae were suggested to have acted as ‘snowshoes’ that prevented sinking into the substrate (Fortey and Gutiérrez-Marco, 2022), conducive with the ‘mud-shoe’ hypothesis proposed for the broad harpid, though not trinucleid, brim (Miller, 1972). Elongate postero-lateral and axial spines in other trilobites have been suggested to perform an antipredatory role (Fortey, 2014; Lynch et al, in press; Pates and Bicknell, 2019; Rustán et al, 2011), particularly when coupled with enrolment behaviour (Chipman and Drage, 2023; Esteve et al, 2011). Indeed enrolment would have orientated the genal prolongations of trinucleids dorsally, in a similar position to some other spines interpreted as antipredatory in many trilobite groups (Fortey and Owens, 1999).…”

Section: Introductionmentioning

confidence: 99%

Hydrodynamic function of genal prolongations in trinucleimorph trilobites revealed by computational fluid dynamics

Pates,

Drage

2024

Preprint

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Trilobites, a diverse clade of Palaeozoic arthropods, repeatedly converged on the trinucleimorph morphology. Trinucleimorphs possessed vaulted cephala with a broad anterior fringe and prominent posteriorly orientated genal prolongations. Various functional hypotheses have been proposed for the fringe, however the possible function of the genal prolongations has received less attention. Here we use a computational fluid dynamics approach to test whether these prolongations served a hydrodynamic function: generating negative lift to allow trinucleimorphs to remain in place on the seafloor and prevent overturning within fast flowing water. We simulated the performance of cephala with broad, narrow, and absent genal prolongations in a benthic environment with flow speeds ranging from 0.05 to 0.5 m s-1, in two cephalic postures. The first posture had the anterior of the cephalon parallel to the seafloor, while for the second the genal prolongations were parallel to the seafloor. Posture and presence of genal prolongations were found to be important for generating negative lift, with performance improving under faster flow speeds. No significant difference between narrow and broad genal prolongations was detected. This study provides support for genal prolongations serving a hydrodynamic function, similar to the femurs of some insect larvae, however, it does not preclude prolongations also serving additional functions as snowshoes or antipredatory deterrents.

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Trilobites in rock enrol: a comment on ‘Developmental and functional controls on enrolment in an ancient, extinct arthropod’ by Esteve and Hughes (2023)

Cited by 4 publications

References 15 publications

Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods

Convergent evolution of ventral adaptations for enrollment in trilobites and extant euarthropods

Convergent evolution of ventral adaptations for enrolment in trilobites and extant euarthropods

Hydrodynamic function of genal prolongations in trinucleimorph trilobites revealed by computational fluid dynamics

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