The early bird gets two tails? A 120-million-year-old bird sported a long tail and a second, unexpected tail frond, paleontologists suggest. The discovery points to a complicated evolutionary path for the tails we see in birds today.
One of the oldest known birds, Jeholornis, lived in what is today China, along with a trove of other feathered dinosaurs discovered in the region over the last decade. It was also thought to sport only a long fan-feathered tail at its back end. Now, however, paleontologists are claiming discovery of a second tail frond adorning the bird. (See "Did Feathered Dinosaurs Shake Their Tail Feathers?")
"The 'two-tail' plumage of Jeholornis is unique," according to the study, which was led by Jingmai O’Connor of the Chinese Academy of Sciences in Beijing. The report of the discovery of the tail frond was published in the Proceedings of the National Academy of Sciences.
Of 11 Jeholornis fossils that retain evidence of ancient plumage, 6 have signs of this frond of 11 feathers, which would have jutted above the bird's back at a jaunty, upright angle in a "visually striking" manner, according to the study.
"Clearly the display aspect of the frond would have been undeniable," says paleontologist Mark Norell, of the American Museum of Natural History in New York, who was not part of the study. "It calls to mind living birds, even peacocks, which display broad plumes of feathers."
In peacocks and other birds, such feathery features are more for attracting the attention of potential mates than for any functional purpose.
Since male birds today are the ones with the striking plumage, the authors suggest that perhaps only one sex of Jeholornis sported the eye-catching tail fronds.
Early Aviation Advantage?
Jeholornis is not thought to be directly related to modern birds, which seem to have evolved from a different line of early avians. The study authors suggest that the tail frond may have played a stabilizing role in the flight of these early birds and that if the arrangement of feathers had proven advantageous enough, modern birds might have evolved to sport such two-tailed features. They see the fronds as flattening to offer a streamlined appearance when the bird was in flight.
Other researchers aren't convinced the newly discovered tail frond played much of a role in aviation, however.
"Feathering in the new specimens is quite interesting, but we have to remember it is a feature so far only known in one species," says University of Texas paleontologist Julia Clarke, who adds the frond wasn't seen in all the fossils.
"Thus, its implications for the origin of flight are unclear," she says. "It could have been a peculiarity of the one species, as the authors note."
Perhaps more likely, she suggests the frond simply evolved as an easy-to-notice "sexual display" flaunted by these early birds.
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