A chelicera-bearing arthropod reveals the Cambrian origin of chelicerates

Megachelicerax cousteaui holotype KUMIP 314091a,b directly preserves massive three-segmented chelicerae, five post-cheliceral prosomal limb pairs and lamellate opisthosomal appendages; predation and its bridging stem-chelicerate position are functional and phylogenetic interpretations.

Megachelicerax cousteaui gen. et sp. nov. is described from holotype KUMIP 314091a,b; the profiled stem-chelicerate assignment remains a phylogenetic result, not direct ancestry.

This profile is restricted to the Drumian Wheeler Formation holotype from Utah and does not establish a global Megachelicerax distribution.

Large predatory ecology is inferred from massive chelicerae and body-plan comparisons; prey, behaviour and locomotor performance are not directly preserved.

KUMIP 314091a,b directly preserves massive three-segmented chelicerae, five pseudobiramous post-cheliceral prosomal limb pairs and plate-like lamellae-bearing opisthosomal appendages.

Bayesian and parsimony analyses recover Megachelicerax on the chelicerate stem between sampled Cambrian habeliids and post-Cambrian synziphosurines; this topology is not a direct ancestor–descendant sequence.

Megachelicerax is bounded here by holotype KUMIP 314091a,b from the Drumian Wheeler Formation of Utah; this named holotype context is not a global distribution or exact complete range.

The 519–500.5 Ma stem-chelicerate evidence route links the Chengjiang Urokodia and Wheeler Megachelicerax samples and does not represent one lineage's temporal duration.