Ancient arachnid claws
A fist-sized fossil collected in Utah in the 1970s was re-examined and found to preserve claws from Megachelicerax cousteaui, an early relative of spiders and scorpions. The specimen—about 50 years in museum collections—shows anatomical details that push back what we can read from old finds about early arachnid limbs (x.com).
Chelicerates are the arthropods that feed with front claws instead of antennae, and a Utah fossil now shows those claws 500 million years ago. (nature.com) That fossil belongs to *Megachelicerax cousteaui*, a newly described soft-bodied animal from the middle Cambrian Wheeler Formation in Utah’s West Desert. Rudy Lerosey-Aubril and Javier Ortega-Hernández reported it in *Nature* on April 1, 2026. (nature.com) Modern chelicerates include spiders, scorpions, mites, ticks, horseshoe crabs, and sea spiders. Their defining tool is the chelicera, a pincer-like feeding appendage at the very front of the body. (nature.com) Early fossils from this branch had long been disputed because they lacked clear chelicerae. The new specimen preserves “massive three-segmented chelicerae,” giving researchers an unambiguous example from the Cambrian period. (nature.com) The animal was a large sea predator, a little more than 8 centimeters long, with a head shield and nine body segments. Lerosey-Aubril said he spent more than 50 hours cleaning the fossil under a microscope with a fine needle before the claw became clear. (mcz.harvard.edu) The specimen was collected in Utah in the 1970s and then sat in collections for decades before this re-examination. The study says old museum material can still preserve anatomical details detailed enough to redraw early arthropod family relationships. (mcz.harvard.edu) Before this, the oldest known chelicerates came from the Early Ordovician Fezouata Biota of Morocco, about 480 million years ago. *Megachelicerax* pushes that record back roughly 20 million years. (mcz.harvard.edu) The fossil also preserves five pairs of front body limbs and plate-like structures under the rear body that resemble the book gills of modern horseshoe crabs. In the authors’ evolutionary analyses, that anatomy places *Megachelicerax* on the stem of the chelicerate lineage, between older Cambrian forms and later claw-bearing relatives. (nature.com) The result is a simpler picture of the problem paleontologists were trying to solve: when did the spider-and-scorpion body plan first appear? This Utah fossil says the answer is the Cambrian, and that the clue was sitting in a museum drawer for about 50 years. (nature.com)
