You may see red, but you can’t see it like some birds and turtles or the ancient “eagle-lizards” from which they came. According to a study published this month in Proceedings of the Royal Society B, a “red gene” that originated from dinosaurs isn’t just responsible for the red patterns on some birds and some turtles. It also gives them special color vision, allowing them to see differences in shades of red that aren’t detectable to humans.
Most humans can see scarlet and crimson, but the animals with the gene can pick out the shades in between, so two birds that look the same to us appear different to birds with the gene. Known as CYP2J19, the gene comes from the same group that produces enzymes in humans allowing us to break down drugs and toxins in the body, said Nicholas Mundy, an evolutionary geneticist at the University of Cambridge who led the study.
In birds, he’s found that the red gene converts carotenoids, pigments primarily found in plants, from yellow to a red oil that coats the retina like a lens, augmenting color vision.
Researchers traced the gene’s evolutionary history back some 250 million years to the archosaur, a dinosaur-ish creature with the skin of an armadillo, head of a bird, snout of a pig, body of a crocodile and belly of a turtle. Dr. Mundy thinks “it’s quite likely that the dinosaurs would have been bright red” with specialized red-oil pigments on their eyes.
The scientists think birds and turtles are the only land animals that still have the red gene. Snakes and scaly lizards split from the archosaur before turtles and lack the red oil on their retinas. Dr. Mundy thinks crocodiles, which spent a lot of time as nocturnal animals, lost the gene because seeing red food wasn’t as important.