Cambrian Fossil Sheds Light on Early Evolution of Spider Fangs

A collaborative team from Yunnan University and the University of Leicester has described a 2-3 cm Cambrian animal, Urokodia, whose fossil was recovered from the Chengjiang deposits in southern China. Advanced X-ray scanning revealed soft-tissue details, including a pair of pincer-shaped limbs situated just behind the creature’s stalked eyes, interpreted as the earliest chelicerae. These structures are the evolutionary ancestors of the fangs seen in modern spiders and related chelicerates.

Additional features on the legs suggest the presence of book gills, a respiratory organ still found in present-day horseshoe crabs. Published in Nature on the 42nd anniversary of the Chengjiang site's discovery, the work highlights how predatory adaptations were already developing in marine ecosystems more than 500 million years ago. Lead author Yu Liu emphasized the significance of the find for understanding the deep roots of chelicerate evolution.