Tiny light-scattering structures that give today’s butterflies and moths their brilliant hues date back to the days of the dinosaurs.
Fossilized mothlike insects from the Jurassic Period bear textured scales on their forewings that could display iridescent colors, researchers report April 11 in Science Advances. The fossils are the earliest known examples of insects displaying structural color — that is, color produced by light bending around microscopic structures, rather than light being absorbed and reflected as with a pigment or a dye. Structural color is common in bird feathers and butterfly wings today, but finding such features in the fossil record can be tricky.
Scientists know very little about what the scales of ancient butterflies and moths looked like because that level of detail is preserved in very few fossils, says Conrad Labandeira, a paleoentomologist at the Smithsonian Institution in Washington, D.C., who wasn’t part of the work.
For the study, paleobiologist Bo Wang and his colleagues spent three years examining more than 500 fossilized specimens from now-extinct lepidopterans. Most weren’t preserved well enough to still have scale remnants, says Wang, of the Chinese Academy of Sciences in Nanjing. But six Jurassic-era fossils did, the oldest of which was nearly 200 million years old. The researchers examined the microscale wing structures of these specimens under a scanning electron microscope, then used a computer program to figure out what color the wings would have appeared.
The ancient moths’ wings have small scales covered by larger scales, which bear a series of parallel V-shaped ridges that create a herringbone pattern. Similar features are seen in today’s Micropterigidae, a primitive family of moths, Wang says. The size and arrangement of the structures would have allowed the moth wings to scatter light to display a range of iridescent colors, he and his team concluded from the computer analyses.
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Modern moth and butterfly wings have even finer-grain structures than what’s seen in these fossil insects, says Pete Vukusic, a biophysicist at the University of Exeter in England who wasn’t part of the study. But wings are so fragile that it’s possible the ancient lepidopterans also had smaller scale structures that weren’t preserved in the fossil record, he says.