518-Million-Year-Old Fossil Shows Origin of Spider Fangs

On August 4, 2026, scientists announced the discovery of the oldest evidence of structures that would become spider fangs, in a 518-million-year-old fossil. The research, carried out by teams from Yunnan University and the University of Leicester, was published in the journal Nature.

Fossil Found at the Chengjiang Site

The remains of Urokodia were identified at the famous Chengjiang fossil site in Yunnan Province, southern China. The locality, recognized 42 years ago, preserves traces of more than 200 types of animals that inhabited the oceans over half a billion years ago.

Description of Urokodia

Urokodia measured between 2 and 3 cm in length, featuring large stalked eyes at the front of the body, a segmented exoskeleton, and articulated limbs attached to a narrow structure. Traces observed on the legs may have functioned as book gills, enabling underwater respiration, a feature still present in aquatic chelicerates such as seahorses.

Tomography Reveals the Earliest Chelicerae

Using X-ray tomography, the researchers examined the rock encasing the fossil and found that much of the soft anatomy remained mummified for hundreds of millions of years. The scan revealed two pincer-like appendages located just behind the eyes, representing a primitive form of chelicerae that, in modern species, can function as pincers or fangs.

Professor Yu Liu explained: "We were using X-ray tomography analysis of these fossils to reveal their soft anatomy buried in the rocks for hundreds of millions of years, when suddenly we noticed the pincer-like limbs at the front of the animal. We knew immediately that this was a very exciting fossil and indeed a distant ancestor of living chelicerates like scorpions and spiders."

Connection to Spiders and Scorpions

Spiders belong to the broad group of chelicerates, which also includes scorpions and ticks, totaling more than 100 000 described species. The distinctive element of these animals is the chelicerae, frontal appendages that can function as pincers or fangs to grasp, pierce, or stab prey.

Professor Mark Williams added: "Urokodia was part of an ancient ecosystem of over 200 different types of animals living in the seas over 500 million years ago. These spectacularly preserved fossils provide real insights into how life was evolving on our planet at the very dawn of animals."

Significance for the History of Life

Chelicerates are among the most successful animal groups in marine and terrestrial environments. Those that migrated onto land became effective predators, and the fossils show that their ancestors were already hunting hundreds of millions of years ago. The discovery of Urokodia provides a unique window into how the earliest pincers evolved and gave rise to the feared fangs of modern spiders.

With information from ScienceDaily.