Many living birds have mastered the art of the shimmer. The iridescent feathers on hummingbirds, for instance, capture and split the light, producing gorgeous rainbow patterns that earn them descriptive names like emerald, ruby, and sapphire. Such flair is not limited to hummingbirds; in the right light, even the humble city pigeon sports flashy neck feathers.
Now scientists have evidence of their Jurassic counterpart. An international team of paleontologists have announced the discovery of Caihong, a chicken-size dinosaur with the earliest known iridescent feathers.
Most feathered theropods of Late Jurassic China share a near-identical build—small and fluffy, with winged arms and legs—and Caihong, which is known from a complete skeleton, doesn’t buck the trend. But when paleontologist Julia Clarke from The University of Texas at Austin used a scanning electron microscope to take a closer look at its feathers, her lab found something out of the ordinary: microscopic remains of melanosomes—bundles of pigment responsible for color in most animals—on feathers from its head, chest, and parts of the tail. All three spots are common display areas in modern birds.
Melanosomes found on other dinosaurs, including the closely related Anchiornis, suggest duller patterns of brown, gray, and red. Caihong was fancier: Melanosomes on its head and chest were organized in sheets of long, flat proteins, which act like miniature prisms. It’s the kind of arrangement that gives hummingbirds their particular jewel-like glimmer. While the original color of the fossilized feathers is unknown, Clarke says, such a find suggests that Caihong’s chest shone with shifting hues.
Caihong might not have relied solely on its feathers to show off. It also had a bony head crest shaped like a little horn in front of its eyes, of a kind more commonly seen in big predatory dinosaurs like Allosaurus. The exact functions of such horns aren’t nailed down, but they’re often suspected to have a role in social behavior such as mate attraction or dominance. But these display organs are seldom seen on small, feathered dinosaurs or their flying descendants. “These crests seem to disappear in the part of the family tree where theropods are getting smaller and more bird-like,” says Steve Brusatte, a paleontologist with the University of Edinburgh. “It’s most likely that the crest re-evolved [in this dinosaur] because none of Caihong's closest known relatives have one.”
Whether Caihong could fly is an open question, although it’s unlikely that it was comfortable in the air. “Even if it didn't fly, those wings and iridescent feathers would have been great display structures,” Brusatte says. “Add them together with the head crest and you have one glammed-up dinosaur that would have looked really flamboyant.”
Between the feathers and crest, Caihong provides further evidence that visual displays were important to early feathered dinosaurs, just as they would go on to be for modern birds.