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A chelicera-bearing arthropod reveals the Cambrian origin of chelicerates


Abstract

Chelicerata is a megadiverse (over 120,000 species) arthropod clade that includes familiar taxa of profound ecological and economic importance, such as scorpions, spiders and mites1. Extant chelicerates share a unique anatomical character, the chelicerae—feeding first appendages terminated by a simple pincer-like chela2. The fossil record of these primarily predatory animals spans almost 500 million years3, suggesting a likely yet undocumented origin during the Cambrian Explosion. Artiopods4,5,6, megacheirans4,7,8,9, habeliids10,11,12,13 and mollisoniids14,15 have been considered Cambrian stem- or crown-group chelicerates, but they all lack unequivocal chelicerae, leaving the emergence of chelicerae-bearing arthropods unclear. Here we describe Megachelicerax cousteaui gen. et sp. nov., a large soft-bodied arthropod from the middle Cambrian of Utah featuring massive three-segmented chelicerae, along with five pairs of pseudobiramous prosomal limbs with non-foliaceous exopodal rami, and plate-like lamellae-bearing opisthosomal appendages. Bayesian and parsimony phylogenetic analyses resolve Megachelicerax as a stem-group chelicerate bridging Cambrian habeliids and post-Cambrian chelicerae-bearing synziphosurines. This finding provides unequivocal evidence of large predatory chelicerates in the Cambrian, illuminates their body plan’s origin, and confirms habeliids, mollisoniids and probably megacheirans as members of total-group Chelicerata.

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Fig. 1: M. cousteaui gen. et sp. nov. from the Cambrian (Drumian) Wheeler Formation of Utah.
Fig. 2: External morphology of M. cousteaui gen. et sp. nov.
Fig. 3: Evolution of deutocerebral raptorial appendages in total-group Chelicerata.

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Data availability

All data analysed in this paper are available within the Article and its Supplementary Information, except for the morphological dataset, which is archived on Figshare55. The nomenclature of M. cousteaui gen. et sp. nov. has been registered in ZooBank under the following LSIDs: urn:lsid:zoobank.org:pub:0F9A12CA-06A7-416C-B89E-E014AFA1363E (publication); urn:lsid:zoobank.org:act:40631BDF-FECD-4A1C-BE3E-ABAFFE6BC563 (genus); and urn:lsid:zoobank.org:act:A1CAB82A-C6EF-45B4-B19B-52F265B1D0FD (species).

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Acknowledgements

We thank L. Gunther for donating the holotype of M. cousteaui gen. et sp. nov. to the Biodiversity Institute of the University of Kansas (KUMIP); B. Lieberman and J. Kimmig (KUMIP) for curatorial assistance; M. Hattori for the illustrations in Fig. 2b; D. E. G. Briggs, J. Cabra García, J.-B. Caron, J. Christophoryová, R. J. Garwood, E. Gonzáles Santillán, S. Hu, P. Klimov, J. C. Lamsdell, Magnolia Press, G. S. Miranda, O. Mirshamsi, A. S. P. S. Reboleira, D. J. Siveter, D. J. Siveter, M. Souza, D. A. Staples, M. D. Sutton and C. K. Taylor for permission to reproduce images. This research was funded by the Human Frontier Science Program (RGY0056/2022), and the Dean’s Competitive fund for Promising Scholarship of the Faculty of Arts and Sciences and the Wetmore Colles Fund of the Museum of Comparative Zoology at Harvard University.

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Contributions

R.L.-A. and J.O.-H. designed the project. R.L.-A. prepared and photographed the specimen. R.L.-A. made anatomical interpretations and descriptions with inputs from J.O.-H.; J.O.-H. developed the phylogenetic dataset and analyses with inputs from R.L.-A.; R.L.-A. and J.O.-H. prepared the figures. R.L.-A. led manuscript preparation and writing and both of the authors contributed to editing the manuscript.

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Correspondence to
Rudy Lerosey-Aubril or Javier Ortega-Hernández.

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Nature thanks James Lamsdell, Lorenzo Lustri and the other, anonymous, reviewer(s) for their contribution to the peer review of this work. Peer reviewer reports are available.

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Extended data figures and tables

Extended Data Fig. 1 Part (KUMIP 314091a) of the holotype of Megachelicerax cousteaui gen. et sp. nov.

a, General view. b, Interpretative drawing. hs, haemolymphatic (lacunar?) system. Other abbreviations as in Fig. 1. Scale bars, 5 mm.

Extended Data Fig. 2 Counterpart (KUMIP 314091b) of the holotype of Megachelicerax cousteaui gen. et sp. nov.

a, General view (mirrored). b, Interpretative drawing. The haemolymphatic system may be preserved either alone (‘exposed’) or within the appendages (‘underlying’). Abbreviations as in Fig. 1. Scale bars, 5 mm.

Extended Data Fig. 3 Structure of the chelicera in selected fossil and extant chelicerates.

a–c, Multisegmented chelicerae (four or more podomeres). a, Synziphosurine Dibasterium (Silurian, Wenlock). b, Synziphosurine Offacolus (Silurian, Wenlock). c, Pycnogonid Ascorhynchus (extant). d–k, Pincer-type or scissor-type three-segmented chelicerae. d, Pycnogonid Nymphon (extant). e, Megachelicerax gen. nov. (Cambrian, Drumian). f, Eurypterid Pentecopterus (Ordovician, Darriwilian). g, Parasitiform mite Stratiolaelaps (extant). h, Opilione Rhampsinitus (extant), reproduced with permission from the copyright holders, C. Taylor/Magnolia Press62. i, Xiphosurid Limulus (extant). j, Palpigrade Eukoenenia (extant). k, Scorpion Mesomexovis (extant). l, m, Pincer-type or scissor-type two-segmented chelicerae. l, Solifuge Galeodes (extant). m, Pseudoscorpion Chtonius (extant), reproduced with permission from J. Christophoryová63. n, o, Jackknife-type two-segmented chelicerae. n, Amblypyge Sarax (extant), adapted from ref. 64, under a CC BY 4.0 licence. o, Spider Glenognatha (extant), reproduced with permission from the copyright holders, J. Cabra-García/Magnolia Press65. Images courtesy of M. Sutton, D. Briggs, D. Siveter, D. Siveter (a, b), and R. Garwood (b), D. Staples (c, d), J. Lamsdell (f), P. Klimov (g), C. Taylor/Magnolia Press (h), M. Souza (j), E. Gonzáles Santillán (k), O. Mirshamsi (l), J. Christophoryová (m), G.S. Miranda and A.S.P.S. Reboleira (n), and J. Cabra-García/Magnolia Press (o). Numbering of podomeres from proximal to distal. Scale bars, 2 mm (f), 1 mm (a, e, h, i, k, l), 500 μm (c, d, n, o), 200 μm (b), 100 μm (m) and 50 μm (g, j).

Extended Data Fig. 4 Prosomal appendages of Megachelicerax cousteaui gen. et sp. nov. and Cambrian habeliids.

a–n, Close-ups and interpretative drawings of the post-cheliceral prosomal appendages of M. cousteaui. a–d, Right (a, b) and left (c, d) exopodal rami 2. e–h, Left (e, f) and right (g, h) exopodal rami 3. i, j, Left exopodal ramus 4. k, l, Left exopodal rami 5 (right) and 6 (left). m, n, Endopodal rami 2–5. o, p, Close-ups of the prosomal appendages of Sanctacaris uncata (o) and Habelia optata (p) (Cambrian, Wuliuan), adapted from ref. 13 under a CC BY 4.0 licence. Images courtesy of J.-B. Caron (o, p). Numbering of exposed podomeres from proximal to distal. ds, distal spine; ei, endite; tc, terminal claw. Other abbreviations as in Fig. 1. Scale bars, 2 mm (m–p) and 1 mm (a–l).

Extended Data Fig. 5 Opisthosomal appendages of Megachelicerax cousteaui gen. et sp. nov. and xiphosurid chelicerates.

a–g, Close-ups and interpretative drawings of the opisthosomal appendages of M. cousteaui. a, Left opisthosomal appendages 1–4, part. b, c, Detail of (a) showing the partial overlap of the gill plate by gill lamellae. d, e, Opisthosomal appendages 2 and 3, counterpart. f, g, Detail of (a) showing the imbricated gill lamellae. h, Two consecutive gill opercula of the Triassic xiphosurid Yunnanolimulus (mirrored), adapted from ref. 66 under a CC BY 4.0 licence. i, Left half of a gill operculum of the recent xiphosurid Limulus. j, Gill of the recent xiphosurid Limulus; the arrangement of gill lamellae was disturbed to better illustrate the membranous nature of the lamellae. Image courtesy of S. Hu (h). el, endopodal lobe; sl, sternal lobe; xl, exopodal lobe. Other abbreviations as in Fig. 1. Scale bars, 5 mm (a, d, e, i, j), 2 mm (b, c, f, g) and 1 mm (h).

Extended Data Fig. 6 Comparison of results from Bayesian inference and parsimony-based phylogenetic analyses.

a, Consensus tree resulting from Bayesian analysis in MrBayes. Mk model, four chains, 5,000,000 generations, 1/1000 sampling resulting in 5000 samples with 25% burn-in resulting in 3750 samples retained. Numbering denotes node posterior probability values. b, Strict consensus resulting from equal-weight parsimony analysis. c–f, Strict consensus trees resulting from implied-weights parsimony analyses with concavity values k of 1 (c), 2 and 3 (d), 4 (e), and 5 to 10 (f). The position of Pycnogonida highly varies affecting the compositions of Chelicerata sensu stricto (i.e., chelicera-bearing chelicerates) and Euchelicerata (i.e., Chelicerata sensu stricto other than pycnogonids). Note that the results from implied-weights parsimony with low concavity values illustrated in (c) and (d) appear least plausible, since a crownward position of the chelicera-lacking Habeliida relative to the chelicera-bearing Synziphosurina would require multiple major evolutionary reversals at the origin of habeliids (e.g., loss of chelicerae; acquisition of biramous opisthosomal appendages with lobate exopods and marginal setae).

Extended Data Fig. 7 Schematic model of segmentation in selected total-group Chelicerata.

Tagmata are primarily identified using appendicular anatomy and represented by distinct colours. Various shades of red and blue are used to denote variations in appendicular anatomy between segments of the anterior tagma and intermediate tagma, respectively. Numbers in parentheses refer to stratigraphical stages; for instance, Cambrian 5 means the fifth stage of the Cambrian System or Wuliuan Stage. Anatomical data from7,8,11,13,14,25,38,41. Our reconstructed appendicular anatomy of Mollisonia differs slightly from14 to acknowledge the facts that only one cephalic exopodal ramus has been documented so far (tentatively assigned to the 7th segment of the anterior tagma) and the pygidium is composed of three, not four segments66. We also follow Dunlop & Lamsdell’s reinterpretation of Dibasterium38, which considers the presence of six, rather than seven appendage-bearing prosomal segments (contra25), and believe that gill lamellae in at least the mesosomal appendages of Offacolus have been well-documented24 (contra38).

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Lerosey-Aubril, R., Ortega-Hernández, J. A chelicera-bearing arthropod reveals the Cambrian origin of chelicerates.
Nature (2026). https://doi.org/10.1038/s41586-026-10284-2

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