Our oldest known vertebrate ancestors had four eyes to spot predators — and, my goodness, they were cute.
Rare fossils from China have revealed that the earliest recorded creatures with spines — jawless fish from half a billion years ago — were equipped with two sets of peepers. Researchers have released an adorable reconstruction of one such four-eyed noodle as part of a study that described the two pairs of eyes, which were surprisingly advanced for their time.
Humans come from a long line of vertebrates that researchers can trace back to these jawless fish, called myllokunmingids. Most of our relatives have two eyes just as we do, but it seems myllokunmingids needed more.
Myllokunmingids lived 518 million years ago, during the Cambrian period (541 million to 485.4 million years ago). During this time in Earth’s history, large predators were beginning to emerge, making the ocean more dangerous for our small, soft-bodied ancestors.
“In that environment having four eyes may have given these animals a wider field of view — important to avoid predators,” Vinther said.
Researchers discovered the eyes in exceptionally detailed fossils preserved in the Chengjiang fossil beds in southern China. In two separate species — Haikouichthys ercaicunensis and an unnamed myllokunmingid species — fossils were found to have two larger eyes on both sides of their heads and two smaller eyes in the middle of their heads, according to the study.
Because soft body parts like eyes are rarely preserved in the fossil record, the researchers were fortunate to find the remains of any eyes in the fossils, let alone four. To confirm the existence of the eyes and examine their structure, the team used high-powered microscopes and chemical analysis.
“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 lead author Peiyun Cong, a research professor of paleobiology at Yunnan University in China, said in the statement. “Seeing that was incredibly exciting.”
The two smaller eyes were circular, with light-absorbing pigments and lenses that could form images, just like the larger eyes, according to the researchers. The team thinks the second pair of eyes represents the ancestral origins of a more primitive eye-like feature in some modern vertebrates and a gland, which, in humans, helps us sleep.
Some living fish, reptiles and amphibians have a parietal eye, or “third eye,” on their heads that detects light only. This parietal eye is tied to the pineal gland, which, in humans and most other vertebrates, is located in the brain. The pineal gland produces the hormone melatonin when it’s dark, which, in turn, helps us fall asleep. But half a billion years ago, the precursor to this gland was helping myllokunmingids escape predators.
“What we’re seeing is that the pineal organs began as image-forming eyes,” Cong said. “Only later in evolution did they shrink, lose visual power, and take on their modern role in regulating sleep.”
