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New Fossil Fish Discovery Suggests Color Vision at Least 300 Million-Years-Old

fish fossil

Image credit: Fossilized Acanthodes bridgei with eye tissues intact / Tanaka et al., Nature Communications

Just like human beings, the visual system of fish is dependent on the retina’s light-sensitive receptors known as rods which are twilight vision and cones responsible cones for daylight vision.

Based on examination of 300-million-year-old fish, scientists have found the fossilized rods and cones for the first time ever.   They have published their latest research in the recent edition of Nature Communications and such findings demonstrates  that these visual receptors, namely color vision, have existed  in vertebrate eyes for that long as well.

Compared with calcified lenses of some crustaceans and trilobites, most parts of the vertebrate visual system are not well-preserved in the fossil record. Although vision might  have seen for 520 million years at least, soft tissue in both the eye and the brain would become decayed so rapidly, in normal case it would happen within 64 and 11 days after death respectively.

Gengo Tanaka and his team from Kumamoto University has examined the remains of a fish called Acanthodes bridgei which is well-preserved in the Upper Carboniferous Hamilton Formation in Kansas. According to the report by Science, being buried in oxygen-low sediment right after dying such fish remained in the condition that could prevent microbes from being decayed on all its tissues. This species is regarded as the last common ancestor of modern jawed fishes including sharks and all bony fishes. This fish became extinct nearly 250 million years ago at the end of the Permian. With a long, streamlined body with spines, such fish would possibly swim in shallow, brackish waters like Rhinogobius, a fish that can be seen today with similar sized eyes.

To the surprise of researchers, the original color and shape of its dark brown eumelanin (a light-absorbing retinal pigment) were well-preserved. At the same time, scientists also discovered the mineralized rods and cones, that means that it is more likely for the fish to see in color. That would be vital for it to look for food and identify predators in water which was shallow and light-penetrating as well. Therefore, based on these newest these findings, it is suggested that retinomotor activity which is known as light-dependent vision today should have existed as early as 300 million years ago.

Journal reference: Tanaka, Gengo, et al. “Mineralized rods and cones suggest colour vision in a 300 Myr-old fossil fish.” Nature communications 5 (2014).

Source: Science