Whether it’s the miniscule, tusk-wielding Heterodontosaurus, the enormous, flesh-eating Abelisaurus or the super fast, super scary megaraptors, it’s not difficult to imagine how awe-inspiring a world ruled by dinosaurs must have been. What’s far less clear, though, is what the world looked like through their eyes.
As a new genetics study in the Proceedings of the Royal Society B reveals, they may have been seeing red – quite literally. In fact, they were able to see a wide range of shades of red that, over time, encouraged the evolution of red plumage and shells in their descendants, perhaps for mating purposes. This means the dinosaurs went from seeing red to being red, but this isn't the only color they could see.
“Color vision across the visible spectrum evolved early on in vertebrates, so the dinosaurs also had color vision,” coordinating author Dr Nick Mundy, a reader in evolutionary genetics at the University of Cambridge’s Department of Zoology, explained to IFLScience. “Our study is the first to show they had a specialized kind of color vision, with improved sensitivity in the red part of the spectrum.”
In order to find out what it looked like through the lens of a Tyrannosaurus rex and its dinosaurian brethren, a team of researchers compared the evolutionary lineages of both turtles and birds, both of whom share a common ancestor with non-avian dinosaurs. They were specifically looking at the development of a gene known as CYP2J19, one that allows birds and turtles to convert yellow pigments in their diets into red ones.
These creatures can use these red pigments to “paint” their beaks and feathers for display purposes. This pigment conversion ability also allows them to lace their retinas with red oil droplets, which heightens their color vision across the red spectrum. Effectively, having CYP2J19 enhances their ability to see red, and the researchers hypothesize that the appearance of this gene allowed their ancestors to see shades of red for the first time.
By tracing CYP2J19 back through both of these evolutionary lineages, the researchers were able to calculate that it would have first appeared roughly 250 million years ago, around the time of the end-Permian mass extinction that wiped out almost all life on Earth. It would have initially evolved in archelosaurs, a group that contains turtles and archosaurs, the latter of which comprises all birds, crocodilians, pterosaurs, and, significantly, the non-avian dinosaurs.
“These findings are evidence that the red gene originated in the archelosaur lineage to produce red for color vision,” Mundy concluded.
Ospreys have incredible color vision, and it's likely that dinosaurs did too. Mark Medcalf/Shutterstock
Humans, of course, can differentiate between various shades of red, but birds are able to see far more varieties of red than we are. This rich spectrum of redness is roughly equivalent to our spectrum of reds, blues, and greens, and it’s highly likely dinosaurs possessed this multi-red spectrum too.
Interestingly, the lineage that produced scaly lizards and snakes split from the archelosaurs before turtles and, therefore, before CYP2J19 emerged, meaning that they never got the chance to see in red this way. Some have no retinal pigments, and others have yellow and green variants, but not red.
On the other hand, crocodilians split from the archelosaurs after turtles and initially retained the CYP2J19 gene. However, modern crocodiles are unable to produce retinal red oil droplets, meaning that at some point along the way, they must have lost the gene, with natural selection having deemed it unnecessary for their survival.
As ancient as CYP2J19 is, it isn’t the oldest of its kind. Mundy told IFLScience that “there are many genes involved in coloration and some evolved much earlier.”
Modern birds often have excellent color vision, and they are more closely related to dinosaurs than contemporary crocodiles. This implies that, far from just seeing red, dinosaurs saw the planet in shades of blue, green, and everything in between.
Their ancestors were among the first to develop the all-important red gene. Natursports/Shutterstock