A 500-Million-Year-Old Surprise Is Forcing Scientists to Rethink Spider Evolution

A study in Nature describes Megachelicerax cousteaui, a new chelicerate from the middle Cambrian Wheeler Formation in Utah.

The 8 cm fossil preserves pincer-like chelicera and plate-like respiratory structures resembling book gills.

The find pushes the known origin of chelicerates back about 20 million years and links Cambrian arthropods to later horseshoe crab–like forms.