The way we imagine what dinosaurs looked like has changed significantly over the years thanks to more and more discoveries. A new study adds another possible layer to the story with a species of ancient dinosaur that had ultraviolet fluorescing feathers and horns, potentially used in mating displays. The idea is proposed in a new paper published in the journal Historical Biology.
Many birds and reptiles can see not only in ultraviolet light but they employ it to hunt, mate, and rear their young. A European roller preferentially feeds the most UV-reflective chicks, and in many species of birds, male and female plumage is different under UV light.
The inspiration for this work stemmed from a Twitter discussion between the authors, prompted by co-author Jamie Dunning's work on the photoluminescence of puffin beaks under UV light. Many birds are tetrachromats, meaning they have a fourth cone in their retina that allows them to see in the UV spectrum. Could dinosaurs have this too?
A finding that provides some credence to this hypothesis is the Borealopelta fossil, a species of heavily armored dino that lived 110 million years ago in what is now modern-day Canada. The researchers discovered that the animal, which was 5.5 meters (18 feet) long, had fluorescent materials on the tip of its spines, some of which even had specific patterns.
“It's very easy to propose photoluminescence in the fossil record. It'll be another thing entirely to document it. As we talked about in our paper, numerous minerals fluoresce, and from the fossilization process, many fossils in-turn fluoresce,” lead author Cary Woodruff, from the Royal Ontario Museum, told IFLScience. “Fossil keratinous sheaths could fluoresce simply because of minerals associated with fossilization.”
The UV features could be true coloration or it could be due to chemicals that have accumulated during the fossilization process. Even if they are a true coloration, it doesn’t necessarily mean that it was used in mating rituals or as general visual displays.
“Some structures fluoresce, and the host animal never knows. Our teeth fluoresce because of the biominerals, but we'd never know unless we went to a blacklight party. Some modern animals that are tetrachromatic apparently can't see UV, even though they theoretically have the anatomical capabilities. However, some animals – like budgies – can see UV and have photoluminescent feathers that are incorporated into visual displays,” Woodruff explained.
“Our work was only meant to be a 'what if' paper. What if dinosaurs were tetrachromatic? What if dinosaurs had photoluminescent keratinous structures? If so to all of the above, could dinosaurs have used these in displays? There's a very good chance that we'll never know. But if we can get the scientific community talking, investigating, and most importantly, testing and examining these ideas, then that's scientific progression.”