Overview
- Megachelicerax cousteaui, which a Nature paper published Wednesday describes, is identified as the earliest known chelicerate, pushing the group’s origin back about 20 million years.
- The Middle Cambrian fossil from Utah’s Wheeler Formation dates to roughly 500 million years and preserves a clear pincer-like chelicera where antennae would sit in other arthropods.
- The specimen shows a head shield with nine body segments, six pairs of feeding and sensing limbs, and plate-like respiratory structures that resemble the book gills of modern horseshoe crabs.
- Bayesian and parsimony analyses place the animal as a stem chelicerate, an early offshoot that helps link Cambrian groups such as habeliids to later horseshoe crab–like forms known as synziphosurines.
- Collector Lloyd Gunther found the fossil in 1981 and donated it to the University of Kansas, and more than 50 hours of microscope preparation exposed its anatomy as specialists continue to debate competing claims for the very first record.