Two species of myllokunmingiid fishes that lived in what is now China around 518 million years ago (Cambrian period) possessed two large lateral eyes and two smaller, centrally positioned eyes, according to new research led by Yunnan University paleontologists.
An artist’s reconstruction of a myllokunmingiid with four eyes that helped it see and navigate its ancient world. Image credit: Xiangtong Lei & Sihang Zhang.
The myllokunmingiids are primitive jawless fish that lived during the Cambrian period, a time when animals were rapidly evolving new body plans and senses in response to increasing predation.
These creatures are considered to be the earliest known vertebrate animals.
In a new study, Yunnan University’s Professor Peiyun Cong and colleagues examined the new, exquisitely preserved myllokunmingiid fossils from the famous Chengjiang fossil beds of southern China.
“These fossils preserve the eyes in extraordinary detail,” Professor Cong said.
“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. Seeing that was incredibly exciting.”
According to the researchers, modern vertebrates see mainly using two eyes.
A structure deep in the brain — the pineal gland — helps regulate sleep by responding to light and producing melatonin.
In some fish, amphibians, and reptiles, it can still detect light and is sometimes called a ‘third eye.’
The two new myllokunmingiids show that in the earliest vertebrates, the pineal complex was not a simple light sensor — it was a pair of well-developed eyes capable of imaging the world.
“What we’re seeing is that the pineal organs began as image-forming eyes,” Professor Cong said.
“Only later in evolution did they shrink, lose visual power, and take on their modern role in regulating sleep.”
The scientists used high-powered microscopy to identify melanosomes — pigment-containing organelles responsible for coloration and light absorption in living eyes — in all four eyes of the myllokunmingiids.
A chemical analysis confirmed melanin, the same pigment used in modern vertebrate vision.
Circular structures consistent with lenses indicate these eyes were capable of forming images, not just detecting light, providing direct evidence of advanced visual systems in the earliest vertebrates.
“Fossil eyes are incredibly rare — you wouldn’t expect something as delicate as an eye to survive for hundreds of millions of years,” said University of Leicester’s Professor Sarah Gabbott.
“Yet under the right conditions they can, and when they do, they open a rare window into how extinct animals saw and experienced their world.”
“It was a long shot, but we suspected the eyes in these Chinese fossils might be preserved — and they were, complete with light-absorbing pigments in the retina and lenses capable of forming images, showing just how well our earliest ancestors could see.”
During the Cambrian period, the oceans were a dangerous place. Large predators were emerging, while early vertebrates were small, soft-bodied, and vulnerable.
“In that environment having four eyes may have given these animals a wider field of view — important to avoid predators,” said Dr. Jakob Vinther, a paleontologist at the University of Bristol.
The findings also solve a long-standing mystery about the origin of the pineal gland and provide the oldest known evidence of camera-style eyes in the fossil record.
“This changes how we think about the early evolution of vertebrates,” Dr. Vinther said.
“It turns out our ancestors were visually sophisticated animals navigating a dangerous world.”
The study also suggests that the familiar idea of a vertebrate ‘third eye’ may need an update.
“In fact, these animals didn’t just have a third eye — they had a fourth,” Dr. Vinther concluded.
The discovery is described in a paper published on January 21, 2026 in the journal Nature.
_____
X. Lei et al. 2026. Four camera-type eyes in the earliest vertebrates from the Cambrian period. Nature 650, 150-155; doi: 10.1038/s41586-025-09966-0
