Fossilized Rods and Cones Suggest Ancient Fish Saw in Color

Fossilized rod and cone cells - the kind that allow for vision - were recently discovered in an ancient fish specimen, suggesting that it and others like it saw the world in color for at least 300 million years, according to a new study.

The evolution of vision still largely remains a mystery - it has only just been mapped out in detail in humans. An early creature known as Myllokunmingia, dating back 520 million years ago, supposedly had a camera-like eye, but this study is the first to find direct evidence of photoreceptors from a vertebrate eye, researchers report in the journal Nature Communications.

Acanthodes bridge, the last known common ancestor of modern jawed fishes such as barracudas and sharks, was first found in Kansas and has since been held at the National Museum of Nature and Science in Tokyo. Fossils from this area are remarkably well preserved, according to the Los Angeles Times, because sediments from a lagoon buried them very quickly.

In the case of this 10-centimeter-long fish, the preservation process allowed its fossilized rod and cone cells to stay intact for future study.

"Rods and cones are not usually preserved, because these soft tissues are more fragile," lead study author Gengo Tanaka, a paleontologist at Kumamoto University in Japan, told Live Science.

Rods and cones are the cells that line the retina in our eyes. Rods are long and thin and allow us to see at night, while triangular cones are responsible for color vision. Both these cells rely on pigments to absorb light. Via chemical analysis, Tanaka and his colleagues found granules in the fossil made of melanin - a pigment that absorbs light and helps animals see.

A. bridgei was alive approximately 300 million years ago, so the findings indicate that fish may have been swimming around in a colorful world for at least that long.

This research is important because "we can reconstruct what colors extinct animals - example, dinosaurs - could see," Tanaka added.

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