Three-hundred-million-year-old fossil fish still has intact eye tissue

Tanaka et al., Nature Communications

Three-hundred-million-year-old fossil fish still has traces of eye tissue

Researchers have unearthed a fossil fish so well preserved, it still has traces of eye tissues. What’s more, these fossil tissues reveal that the 300-million-year-old fish called Acanthodes bridgei (pictured), like its living relatives, possessed two types of photoreceptors called rods and cones—cells that make vision possible. This is the first time that mineralized rods and cones have been found conserved in a vertebrate fossil, the team reports online today in Nature Communications, as soft tissues of the eye normally begin to disintegrate within days of death. The discovery of cones, which help the eye see colors, is suggestive of the presence of color vision in fish for at least 300 million years. In addition to rods and cones, the researchers detected a dark brown melanin pigment in the fish eyes. All three would have aided daylight and twilight vision in the fish that once thrived in shallow brackish waters. The fossilized fish, which was dug out from an ancient estuarine deposit near Hamilton in Kansas, is similar in size to its distant relative Rhinogobius, a small 4.5-cm-long streamline-bodied goby fish kept as an aquarium pet. According to the researchers, the fossil is so well preserved because the fish would have been buried in oxygen-low sediment soon after dying, preventing bacteria from fully breaking down its tissues.

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