The lineage went “from seeing red to being red.”
250 million years ago, before the rise of the dinosaurs, the eyes of their ancestors began to see the color red in a whole new way.
Writing in the journal Proceedings of the Royal Society B, researchers have found that these ancestors, from which turtles and modern birds also descended, carried the gene CYP2J19.
This gene allows birds and turtles to convert the yellow pigments in their diets into the red ones that tint their feathers, beaks, or shells. Some of these red pigments also end up getting dissolved in oil droplets in their retinas, acting as filters through which light entering the eye is modified to enhance red spectrum vision.
“By filtering the incoming light, the oil droplets lead to greater separation of the range of wavelengths that each cone responds to, creating much better colour sensitivity,” explains Nick Mundy from the University of Cambridge, in a press release.
The retinal oil droplets, which also come in bright green and yellow, are present in birds and turtles, but not in mammals. “Humans can distinguish between some shades of red such as scarlet and crimson,” he says. “However, birds and turtles can see a host of intermediate reds between these two shades, for example.”
By mining genetic data of various bird and reptile species to reconstruct the evolutionary history of the CYP2J19 gene, the researchers concluded that the gene was likely present in dinosaurs and their ancestors.
But the evidence suggests that the gene’s function changed over time. Originally, in the lineage leading up to dinosaurs, the gene improved red color vision. It was only later that it enabled birds and turtles to display brilliant red adornments, taking the lineage “from seeing red to being red,” says Mundy.
The study makes a strong case that dinosaurs would have had the ability to envision a full red spectrum, and the researchers suggest that the gene could have also added red hues to the dinosaurs’ skin.
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