The fossil was discovered in the Jehol Biota – an ecosystem that dates back 133 to 120 million years ago – in northeast China, and the deposits there are a treasure trove of fossil finds, including examples of ancient flies. The researchers named the species Yuanchuavis after Yuanchu, a mythological Chinese bird.
The bird was likely comparable in size to a modern blue jay. However, its tail reached more than 150% of the length of its body. The study was published Thursday in the journal Current Biology.
“We have never seen this combination of different types of tail feathers on a fossil bird before,” Jingmai O’Connor, study author and paleontologist at the Field Museum in Chicago, said in a statement. O’Connor is Associate Curator, Fossil Reptiles, at the Negaunee Integrative Research Center at the Field Museum.
“It had a fan of short feathers at the base and then two extremely long feathers,” said O’Connor. “The long feathers were dominated by the central spine called the rachis, and then pinnate at the end. The combination of a short tail fan with two long feathers is called a pike tail, we see it in some modern birds like sunbirds and quetzals.”
Yuanchuavis likely flew much like a quetzal, a forest bird that doesn’t have the most extraordinary flight skills, O’Connor said. The spit feathers were large enough to create significant drag, although they were light.
Short tails have been associated with birds that live in harsh environments where, like sea birds, they rely on their ability to fly for their ability to survive. The more elaborate tails are often found on birds that live in forests.
“This new discovery vividly illustrates how the interplay between natural and sexual selection has shaped the tails of birds since earliest history,” said Wang Min, study author and researcher at the Chinese Academy of Sciences, in a statement. “Yuanchuavis is the first documented occurrence of a pintail in Enantiornithes, the most successful group of Mesozoic birds.”
Scientists recognized two different tail structures from other enantiornithins combined in Yuanchuavis.
“The rear fan is aerodynamically functional while the elongated central paired plumes are used for display, which together reflect the interplay between natural selection and sexual selection,” said Wang.
Animals adapt not only to survive, but to help their particular species survive. In this case, Yuanchuavis developed tail feathers that hindered his flight skills and made them more noticeable to predators. The discovery underscores the importance of sexual selection during evolution, O’Connor said.
“Scientists call a trait like a big, nippy tail an ‘honest signal’ because it’s harmful. So if an animal with this disability is able to survive with that disability, it is a sign that it is really fit is, “said O’Connor. “A female bird would look at a male with silly, annoying tail feathers and think, ‘Hell, if he can survive with a tail this ridiculous, he must have really good genes.'”
Elaborately feathered birds are usually males. They are so focused on caring for their feathers that they are not particularly good carers for their offspring. Showy feathers would also attract predators towards nests. But the simpler females stay with their chicks and take care of them.
Although enantiornithins thrived initially, they did not survive the dinosaur extinction 66 million years ago. It’s likely because they lived in forests that were on fire after the asteroid hit, or because they didn’t adapt to rapid growth.
“Understanding why living birds are the most successful group of vertebrate animals on land today is an extremely important evolutionary question, because whatever enabled them to be so successful has likely enabled them to survive a giant meteor as well, who hit the planet when all other birds and dinosaurs went extinct, “said O’Connor.
Fossils don’t always show how sexual selection shapes a species.
“The well-preserved tail feathers of this new fossil bird provide great new information on how sexual selection has shaped the bird’s tail from its earliest stages,” said Wang.
“The complexity we see in Yuanchuavis’ feathers is related to one of the reasons we suspect why living birds are so incredibly diverse, because they can only be divided into different species by differences in plumage and song,” said O’Connor. “It is astonishing that Yuanchuavis suggests that this type of plumage complexity may have existed as early as the Lower Cretaceous.”