Kenneth Glad
A remarkable fossil discovered in southern China has offered scientists a rare glimpse into our distant evolutionary past. The find suggests that some of the earliest vertebrates possessed a feature that today sounds almost mythical.
Four dark eye spots are visible in stone from southern China, pressed into the head of a fish barely an inch long. The animal lived around 518 million years ago, during the Cambrian Period.
The Danish version of Science Illustrated has reported on a January 21 study published in Nature describing the fossil and its implications. The research concludes that some of the earliest known vertebrates possessed four functioning eyes, and that the inner pair may eventually have evolved into the pineal gland, the light-sensitive structure deep in the human brain that regulates sleep cycles.
The pineal gland, sometimes called the “third eye,” forms from the same embryonic tissue as the eyes. Some living jawless fish still retain light-sensitive organs on top of their heads, underscoring that developmental link.
For decades, fossil benchmarks suggested that early vertebrates had comparatively simple visual systems, with strong evidence of advanced, camera-type eyes appearing later in the Paleozoic.
Camera-type eyes are the single-lens design found in humans and most vertebrates, capable of focusing light onto a retina to produce detailed images. If the new interpretation holds, complex image-forming vision emerged much closer to the origin of vertebrates than previously documented.
What the fossils reveal
The specimens were recovered from the Chengjiang fossil site in Yunnan province, a UNESCO World Heritage location known for preserving delicate soft tissues. Between 2019 and 2024, researchers collected multiple examples of myllokunmingids, small jawless fish from Cambrian seas.
When scientists examined the larger, more obvious eyes under magnification, they detected two smaller organs positioned between them. “We started by examining the obvious large eyes to understand their anatomy—and it was a complete surprise to find two smaller, fully functional eyes between them,” study co-author Peiyun Cong said in a statement.
Further analyses identified pigment-bearing melanosomes and rounded structures interpreted as lenses in the central eyes. Together, those features indicate the smaller organs were likely capable of forming images rather than simply sensing light.
Four eyes, apparently all functional
Jakob Vinther, a Danish paleontologist at the University of Bristol and co-author of the study, said the animals “likely could see objects quite well, telling their shape and some degree of three-dimensionality.”
In comments to New Scientist, he added that the four-eye arrangement may have provided an “IMAX-style” field of view.
Not all specialists are convinced by the interpretation. Tetsuto Miyashita of the Canadian Museum of Nature, who was not involved in the research, questioned the idea in remarks to New Scientist, asking, “Does it really make so much sense to have so many prominent eyes on the head?”
The findings feed into a wider discussion about when complex vision emerged in vertebrates.
A separate study published January 28 in Proceedings of the Royal Society B described advanced eyes in 443-million-year-old jawless fish fossils from Scotland.
“I love how our findings fit with work from other groups,” Jane Reeves told BBC Wildlife Magazine, saying that together the studies form “a really well-supported picture of the early evolution of vertebrates.”
Sources: Illustreret Videnskab, New Scientist, BBC Wildlife Magazine, Proceedings of the Royal Society B
