Our oldest ancestors had 4 eyes

The discovery of rare fossils in China shows that the first vertebrates, jawless fish from 500 million years ago, were equipped with 2 pairs of eyes. The researchers described these two pairs of eyes in a study and showed that these structures were unexpectedly advanced for their time.

Humans descended from a lineage of vertebrates that researchers can trace back to these jawless fish called myllokunmingids. Most of our relatives have 2 eyes like us, but myllokunmingids seem to have needed more.

myllokunmingids lived 518 million years ago in the Cambrian period; A period that spans between 541 million and 485.4 million years ago. At this point in Earth’s history, large predators were emerging, making the oceans more dangerous for our small, soft-bodied ancestors.

Winter stated that in such an environment, having 4 eyes may have provided these animals with a wider field of vision and was essential for avoiding predators.

Researchers discovered these eyes in exceptionally detailed fossils preserved in the Chengjiang fossil beds in southern China. According to this study, in 2 separate species, Haikouichthys ercaicunensis and an unnamed species of myllokunmingid, it was found that the fossils had 2 larger eyes on either side of the head and 2 smaller eyes in the middle of the head.

Because soft body parts such as eyes are rarely preserved in the fossil record, researchers were lucky to find eye remains in these fossils. To confirm the presence of eyes and examine their structure, the research team used high-powered microscopes and chemical analysis.

They first looked at the large, conspicuous eyes to understand their anatomy, and it was a complete surprise to discover two smaller, fully functional eyes among them, says Pei Yun Kong, the study’s lead author and a research professor of paleontology at Yunnan University in China. He added that it was extremely exciting to see this.

According to the researchers, the 2 smaller eyes had a circular shape, light-absorbing pigments and lenses that were capable of forming images like the larger eyes. The research team believes that this second pair of eyes is a more primitive feature similar to the eyes of some modern vertebrates and the origin of a gland that helps regulate sleep in humans.

Some living fish, reptiles and amphibians have a third eye or third eye in their head that only detects light. It is a peripheral eye associated with the pineal gland, which is located in the brain in humans and most other vertebrates. The pineal gland secretes the hormone melatonin in the dark, and this hormone in turn helps us fall asleep. But 500 million years ago, this gland helped myllokunmingids escape from predators.

What is observed, Kong said, is that the pineal organs were originally formed as eyes capable of forming images. It was only as evolution progressed that these structures shrank, lost their ability to see, and assumed their present-day role in regulating sleep.