As well as being brightly coloured in normal light, some dinosaurs may have had ultraviolet, fluorescing horns, frills or feathers – and a few species might even have used this glow to attract a mate.
Fluorescence is relatively common among amphibians and several species of bird have fluorescent features, which absorb ultraviolet light and re-emit it at a different wavelength. Those body parts glow under UV light. Puffins have fluorescent patches on their beaks, for instance, and budgerigars have some fluorescent feathers on their heads.
D. Cary Woodruff at the Royal Ontario Museum in Toronto says we now know birds are dinosaurs, and that some dinosaurs had feathers while others had horns, frills and spikes that – like a puffin’s beak – were sheathed in keratin.
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He and his colleagues argued in a new analysis that it makes sense that at least some dinosaurs may have enhanced the appearance of these features with fluorescence.
One dinosaur that may have done so is Borealopelta, a heavily armoured, 5.5-metre beast that lived 110 million years ago. A remarkable 3D fossil of Borealopelta was discovered in Canada in 2011. The creature has a prominent, 60-centimetre spine jutting out from each shoulder. Even today, the tips of those spines are fluorescent, glowing slightly in UV light.
It is possible that this is because fluorescent minerals were incorporated into the spines during the fossilisation process, says Woodruff. But in that case, we might expect the entire spine to fluoresce.
The fact that it is only the tips that do so might hint that this reflects some original biological feature, rather like the distinctly coloured, banded beaks possessed by birds like puffins.
But even if dinosaurs such as Borealopelta had fluorescent features, they might not have served a biological function. For example, there is no strong evidence as yet that the fluorescent patches on a puffin’s beak enhance its ability to attract a mate.
“Just because something can fluoresce doesn’t mean it is used in visual communication,” says Woodruff. On the other hand, research has shown that budgerigars do use their fluorescent feathers for courtship displays.
If some ancient dinosaurs did have fluorescent features, Woodruff says it isn’t implausible that they might have used them in a similar way. “It would be [unusual] if, in all the history of dinosaurs, there was just this one kind – the budgerigars – that incorporated this into visual communication.”
Historical Biology
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