Extraordinary fossils of 518-million-year-old jawless fish suggest that the world's earliest known vertebrates possessed two pairs of eyes. Discovered in south-west China, these ancient creatures from the Cambrian period challenge our understanding of early animal vision. Researchers propose that this extra set of eyes evolved into modern organs like the pineal gland.
Over half a billion years ago, during the Cambrian explosion of life around 518 million years ago, jawless fish known as myllokunmingids roamed ancient seas. Fossils of two species, unearthed by Peiyun Cong at Yunnan University in China and his colleagues between 2019 and 2024 along the banks of Dianchi Lake, preserve not just bones but soft tissues, including eyes.
These specimens from the Chengjiang biota offer a glimpse into the origins of vertebrates. Under electron microscopy, the fossils show a pair of lateral eyes with melanin-containing melanosomes and lens impressions, alongside two smaller central structures that also appear to have lenses. "More strikingly, there is also an impression of a lens in each of the lateral eyes and centrally-positioned eyes," says Jakob Vinther at the University of Bristol in the UK.
The team interprets these as two pairs of camera-type eyes, similar to those in humans, allowing the fish to form images of their surroundings—albeit with four eyes instead of two. Vinther explains that the larger eyes likely provided high-resolution vision, while the smaller ones helped detect approaching threats in predator-filled Cambrian waters. "They likely could see objects quite well, telling their shape and some degree of three-dimensionality," he adds. "They likely also had a broad view of their surroundings, sort of IMAX-style, thanks to their four eyes."
This discovery links to modern anatomy: the central eyes may have evolved into the pineal complex, which in mammals includes the pineal gland regulating sleep through melatonin. "We show [the pineal organs] had a more important function as eyes in the early vertebrates and could create somewhat of a decent image before they evolved into organs regulating our sleep cycle," Vinther notes.
Experts offer mixed reactions. Tetsuto Miyashita at the Canadian Museum of Nature finds the interpretation fascinating but questions the absence of a preserved nose, central to early fish evolution. John Paterson at the University of New England sees it fitting for prey species evading predators in the "weird" Cambrian era. Karma Nanglu at the University of California Riverside calls for full-body mapping to rule out fossilisation artefacts.
The findings appear in Nature (DOI: 10.1038/s41586-025-09966-0), sparking debate on vertebrate sensory evolution.