Common ancestor of all birds was probably iridescent

A genetic study of nearly all living bird species has found that the first one to evolve likely had shiny, colourful, iridescent feathers.

The study, published in Nature Ecology and Evolution, also found, contrary to current belief, more cases of iridescence in birds outside the tropics.

“For decades, scientists have had this hypothesis that there are brighter or more colourful species of birds in the tropics,” says lead author Chad Eliason, a research scientist at the Field Museum in Chicago, US.

“We wanted to find the mechanism to help us understand these trends – how these bright colours got there and how they spread across the bird family tree over time.”

Glittery iridescence, as seen on butterfly wings, jewel beetles and hummingbird chests, is not caused by pigments like other animal colouring. Instead, it’s made by structural colour: layers of clear material reflect light in such a way that it appears coloured.

The researchers collated photos, videos and images of 9,409 bird species , combining information on their iridescence with DNA data. There are currently about 10,000 living species of birds known to science.

They used this information to build a colossal bird family tree and used computer modelling to trace iridescence through the tree.

All modern birds are believed to have descended from a group of birds called Neornithes, which evolved about 80 million years ago.

The model suggests that this Neornithes ancestor had iridescent feathers.

“I was very excited to learn that the ancestral state of all birds is iridescence,” says Eliason, adding that there is other evidence of iridescent bords and feathered dinosaurs in the fossil record.

“So we know that iridescent feathers existed back in the Cretaceous – those fossils help support the idea from our model that the ancestor of all modern birds was iridescent too.”

Eliason says that palaeontologists might find this information useful. “We’re probably going to be finding a lot more iridescence in the fossil record now that we know to look.”

The researchers are still unsure why birds are iridescent.

“Iridescent feathers can be used by birds to attract mates, but iridescence is related to other aspects of birds’ lives too,” says Eliason.

“For instance, tree swallows change colour when the humidity changes, so iridescence could be related to the environment, or it might be related to another physical property of feathers, like water resistance.

“But knowing more about how there came to be so many iridescent birds in the tropics might help us understand why iridescence evolved.”