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| Megachelicerax cousteaui Lerosey-Aubril & Ortega-Hernández, 2026 Artistic reconstruction by Masato Hattori |
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 mites. Extant chelicerates share a unique anatomical character, the chelicerae—feeding first appendages terminated by a simple pincer-like chela. The fossil record of these primarily predatory animals spans almost 500 million years, suggesting a likely yet undocumented origin during the Cambrian Explosion. Artiopods4,5,6, megacheirans, habeliids and mollisoniids 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.
Megachelicerax cousteaui gen. et sp. nov.
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| Megachelicerax cousteaui. Artistic reconstruction by Masato Hattori (© Harvard University). |
Rudy Lerosey-Aubril and Javier Ortega-Hernández. 2026. A Chelicera-bearing Arthropod reveals the Cambrian Origin of Chelicerates. Nature. DOI: doi.org/10.1038/s41586-026-10284-2 [01 April 2026]
