Overview
- The Nature paper, published Wednesday, names Megachelicerax cousteaui and identifies it as the earliest known member of the chelicerates.
- Researchers documented an unmistakable three-segmented chelicera—the pincer-like first appendage that defines this group—marking the first clear Cambrian example.
- The fossil dates to roughly 500 million years ago and phylogenetic tests place it in the stem of the chelicerate lineage, linking Cambrian forms with later horseshoe crab–like relatives.
- The specimen from Utah’s Wheeler Formation measures just over 8 cm and preserves a head shield plus nine body segments, specialized feeding and sensory limbs, and book gill–like respiratory plates.
- Lloyd Gunther collected the fossil in 1981 and donated it to the University of Kansas, where careful re-preparation—over 50 hours under a microscope—revealed anatomy that shows the body plan formed early even as diversification came later.