Bird fossil

The holotype fossil of Yuanchuavis. (Credit: Gao Wei)

CHICAGO, Ill. — Scientists have discovered a prehistoric “peacock” that evolved a large tail for mating purposes rather than flight and lived alongside the dinosaurs. The species is the size of a blue jay with a tail nearly twice the length of its body which made it more difficult to fly. Since many bird species have extravagant mating calls in which they bustle their tail feathers and shake to impress their prospective partners, this species is likely one of the earliest birds that evolved for appearance and sexual purposes.

Researchers discovered the fossil in the 120 million-year-old deposits of the early Cretaceous period in northeastern China and named Yuanchavis after a mythological bird. The bird had a fan of short feathers at the base and two extremely long plumes, called a pintail, seen in some modern birds like sunbirds and quetzals.

Living with the dinosaurs

Fossil of Yuanchuavis, with illustration indicating the fossil’s tail feathers. (Credit: Wang Min et al.)

Yuanchuavis is an enantiornithine, a member of a group that was very successful in the time of the dinosaurs but went extinct along with them. Researchers say the discovery shows how even in their earliest history, natural selection had to pay mind to sexual selection.

“It had a fan of short feathers at the base and then two extremely long plumes. The long feathers were dominated by the central spine, called the rachis, and then plumed at the end. The combination of a short tail fan with two long feathers is called a pintail, we see it in some modern birds like sunbirds and quetzals,” says Dr. Jingmai O’Connor, a paleontologist at Chicago’s Field Museum in a media release.

An illustration showing what Yuanchuavis might have looked like in life. (Credit: Haozhen Zhang)

“Scientists call a trait like a big fancy tail an ‘honest signal’ because it is detrimental, so if an animal with it is able to survive with that handicap, that’s a sign that it’s really fit. A female bird would look at a male with goofily burdensome tail feathers and think, ‘Dang if he’s able to survive even with such a ridiculous tail, he must have really good genes,’” Dr. O’Connor explains.

Discovering the key to surviving extinction?

“Understanding why living birds are the most successful group of vertebrates on land today is an extremely important evolutionary question because whatever it was that allowed them to be so successful probably also allowed them to survive a giant meteor hitting the planet when all other birds and dinosaurs went extinct,” the researcher continues.

“This new discovery vividly demonstrates how the interplay between natural and sexual selections shaped birds’ tails from their earliest history. Yuanchuavis is the first documented occurrence of a pintail in Enantiornithes, the most successful group of Mesozoic birds,” adds Dr. Wing Man, a researcher at the Chinese Academy of Sciences.

“It is well known that sexual selection plays a central role in speciation and recognition in modern birds, attesting to the enormous extravagant feathers, ornaments, vocals, and dances. However, it is notoriously difficult to tell if a given fossilized structure is shaped by sexual selection, considering the imperfect nature of the fossil record. Therefore, the well-preserved tail feathers in this new fossil bird provide great new information about how sexual selection has shaped the avian tail from their earliest stage.”

The findings appear in the journal Current Biology.

South West News Service writer Joe Morgan contributed to this report.

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