Our earliest known vertebrate ancestors had four eyes for spotting predators. And lo and behold, they were cute.
A rare fossil from China reveals that the oldest recorded spine-bearing creature, a 500-million-year-old jawless fish, had two sets of peeping organs. Researchers have published an adorable reconstruction of one such four-eyed noodle as part of a study to explain the two pairs of eyes, which was surprisingly advanced for its time.
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Humans come from a long lineage of vertebrates that researchers can trace back to these jawless fish called the mylocumminidae. Most of our relatives have two eyes like we do, but myllokunmingids seemed to need more eyes.
The Myrocumminidae lived 518 million years ago during the Cambrian period (541 million to 485.4 million years ago). During this period in Earth’s history, large predators began to appear, making the oceans more dangerous for our small, flexible ancestors.
“In that environment, having four eyes may have given these animals a wide field of vision, which is important for avoiding predators,” Vinter said.
Researchers discovered the eye in highly detailed fossils preserved in the Chengjiang Fossil Beds in southern China. The study found that the fossils of Haikouichthys erucaikunensis and two unnamed Myrocumminidae species had two large eyes on either side of the head and two smaller eyes in the center of the head.
The researchers were lucky to find the remains of four eyes in the fossil, as soft body parts like eyes are largely absent from the fossil record. To confirm the existence of the eye and examine its structure, the team used high-powered microscopy and chemical analysis.
“We started by examining the apparently large eye to understand its anatomy, and it was a complete surprise to discover two fully functional small eyes between them,” study lead author Peiyun Kong, research professor of paleontology at China’s Yunnan University, said in a statement. “It was incredibly exciting to see.”
The two small eyes were circular in shape and had similar light-absorbing pigments and lenses that could form images, the researchers said. The researchers believe that the second eye represents more primitive eye-like features in some modern vertebrates and, in humans, the ancestral origin of glands that aid sleep.
Some modern fish, reptiles, and amphibians have parietal eyes, or “third eyes,” in their heads that only detect light. This eye on the top of the head is connected to the pineal gland, located in the brain in humans and most other vertebrates. The pineal gland produces a hormone called melatonin when it’s dark, which helps us fall asleep. But 500 million years ago, the precursors of this gland were helping mylocunminids escape from predators.
“What we’re seeing is that the pineal gland began as an image-forming eye,” Conn said. “It wasn’t until late in their evolution that they shrunk, lost their visual powers, and assumed their modern role in regulating sleep.”
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