New research on 121-million-year-old fossils suggests the bird Longipteryx had no tail feathers. Scientists studied two well-preserved specimens from northeastern China. Alexander Clark said, "In reality, they really are worlds apart in terms of lifestyle and potentially movement." These birds used fluffy body feathers instead of long tail streamers.
Around 121 million years ago, somewhere in modern northeastern China, an early bird took to the skies. If you drew its silhouette, you'd notice something was missing. Unlike any bird alive today, it had no tail feathers.
Longipteryx is one of the most abundant fossils from an early group of birds called enantiornithines. Yet scientists know surprisingly little about its plumage. A new study published in the Journal of Paleontology describes the feathers of two remarkably preserved fossils. They suggest Longipteryx flew unlike any living bird today.
"Even though modern birds are the closest analog we have to enantiornithines … in reality, they really are worlds apart in terms of lifestyle and potentially movement," said Alexander Clark, a paleontologist at the University of Chicago and the Field Museum and lead author of the study.
A bird with teeth
The enantiornithine group was one of the most diverse groups of birds to exist during the Mesozoic. According to the study, much of what we know about them comes from the Jehol Biota, a collection of fossils from northeastern China dating to between 121 million and 131 million years ago.
These fossils are famous for their extraordinary preservation, thanks in part to the ancient volcanic lake environment where they died, which preserved traces of skin, muscles and feathers.
"It's always great to see soft tissues preserved in fossil specimens," Clark marveled. "It's just such a treat."
Longipteryx is one of the few Jehol birds known from multiple specimens. It's easily recognizable by its long snout tipped with curved teeth and is similar in size to modern meadowlarks, the study authors wrote.
Despite this, earlier specimens often lacked well-preserved feathers.
A fluffy rear end
The two new Longipteryx specimens were collected by an amateur fossil collector in Jianchang County, who donated them to the Shandong Tianyu Museum of Nature.
According to the study, almost the entire body, from head to ankle, was covered in dark traces of fluffy body feathers. Only the snouts and feet were left bare.
However, the study noted that the fossils' back ends showed only short tufts of fluff roughly 0.2 to 0.3 inches (4 to 8 millimeters) long. Of the 19 known Longipteryx fossils, none show tail feathers, suggesting this species may never have had them to begin with.
That makes Longipteryx different from its relatives, whose males often sported long ornamental tail streamers likely used to show off.
Modern birds can still fly without tail feathers, the study authors wrote, pointing to instances in which birds shed their tail feathers to escape predators, a process called shock-molting.
But a complete lack of tail feathers may have affected how they flew, Clark said. "Enantiornithines, like Longipteryx, lacked a tail fan of feathers, which, in modern birds, helps them brake and steer (among other things). So landing may have looked different."
They flew like nothing we know today
The new fossils also allowed the researchers the first proper glimpse of the shape and length of Longipteryx's wing feathers. According to the study, the inner flight feathers were just over half as long as the outer ones. This suggests Longipteryx had a wing, somewhat like those of modern warblers, finches and thrushes, which flap continuously or alternate between flapping and short glides.
But the bones tell another story. In birds, flight muscles attach to a ridge in the upper arm bone. In Longipteryx, that ridge is long and weak, much like in modern gliding birds such as vultures. Its half-moon-shaped shoulder joint also suggests it could not swing its wings as high as modern birds.
"Enantiornithines may have not been able to bring their wings all the way above their bodies (clapping the wrists), like birds can today," Clark said.
Together, the unique combination of features suggests that Longipteryx and its relatives may have flown in a way unlike anything today.
The researchers caution that the fossils capture only a small part of enantiornithine diversity. Even so, Clark is working to understand what the wing may have looked like when fully stretched out, which may explain exactly how these birds flew through the skies millions of years ago.
"Every new discovery we find in paleontology is another piece of the puzzle of how complex and wonderful life on this planet has been and is," Clark said.