Birds Flew Like Four-Winged Kittyhawk
Xing Xu et al., Science
The fossilized ancient bird Confuciusornis and a close-up of its leg feathers, which some researchers believe formed another pair of wings.
Sept. 15, 2011 --
A stunning array of prehistoric feathers, including dinosaur protofeathers, has been discovered in Late Cretaceous amber from Canada. The 78 to 79-million-year-old amber preserved the feathers in vivid detail, including some of their diverse colors. The collection, published in this week's Science, is among the first to reveal all major evolutionary stages of feather development in non-avian dinosaurs and birds. In this slide, an isolated barb from a vaned feather is visible trapped within a tangled mass of spider's web.
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"These specimens were most likely blown into the tacky resin, or were plucked from an animal as it brushed against resin on a tree trunk," lead author Ryan McKellar told Discovery News. "The fact that we have found some specimens trapped within spider webs in the amber would suggest that wind played an important role in bringing the feathers into contact with the resin," added McKellar, a postdoctoral fellow at the University of Alberta's Department of Earth and Atmospheric Sciences. The feather filaments shown here are similar to protofeathers that have been associated with some dinosaur skeletons.
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McKellar and his team made the discovery after screening over 4,000 amber samples from Grassy Lake, Alberta. The amber, collected by the Leuck family, is now housed at the Royal Tyrrell Museum. The researchers ruled out that the inclusions were mammal hairs, plant or fungal remains based on their structure. Some dinosaur fossils retain skin impressions, so the scientists could match dinosaur protofeathers (hair-like projections) to some of the objects within the amber. Here, a feather is visible near a plant bug. The high number of coils in the this feather suggests it could have come from a water-diving bird.
The translucent tree resin provides a window into feather evolution, from non-avian dinosaurs to birds. "Part of what makes this particular set of feathers interesting is that we find the very simple Stage I and II feathers alongside advanced feathers that are very similar to those of modern birds, Stages IV and V," McKellar said. The researchers aren't yet certain why feathers first evolved, but the density of the protofeathers suggests that they helped dinosaurs with regulating temperature. Dinosaurs such as Troodon or Deinonychus may have produced the feathers. The cork-screw shaped structures in this slide are the tightly coiled bases of feather barbules.
As feathers continued to change, they developed tufts, barbs, branching features, little hooks, and more. Some of the most advanced feathers in the collection are comparable to those of modern grebes. They appear to help diving, indicating that some of the prehistoric birds were divers. McKellar suspects the marine birds might have been Hesperornithiformes, a specialized flightless diving bird from the Dinosaur Era. This is a white belly feather of a modern grebe, showing coiled bases comparable to those seen in the Cretaceous specimen.
Some of the feathers appear transparent now, but would have been white in life. A range of colors for the feathers is evident, though, with grays, reds and various shades of brown preserved. This, and prior research, suggests that non-avian dinosaurs and prehistoric birds could be quite flashy. The pigment within this fossilized feather suggests it would have originally been medium- or dark-brown in color.
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In an accompanying "Perspectives" article in Science, Mark Norell points out that the dinosaur Sinosauropteryx is thought to have had a reddish banded tail, while Anchiornis likely possessed a striking black body, banded wings and a reddish head comb. Norell, chair and curator of the American Museum of Natural History's Division of Paleontology, told Discovery News that the newly discovered feathers are "very exciting." Here, a feather barb within Late Cretaceous Canadian amber shows some indication of original coloration.
Some dino aficionados have wondered if DNA could be extracted from the feathers. "Almost anything is possible," Norell said, quickly adding that most DNA-extraction studies have been conducted on much younger amber, dating to around 20-30 million years ago, and even those led to questionable results. "Maybe bits and pieces could be identified, but not the whole genome." Shown are 16 clumped feathers in Late Cretaceous amber.
People with amber objects, such as jewelry, also probably don't have prehistoric feather inclusions, since such items are extremely rare and dealers isolate the best pieces. Nevertheless, McKellar said, "There is some hope that you could have small feather fragments that have been overlooked." An unpigmented feather and a mite in Canadian Late Cretaceous amber.
The world's first birds all had four wings -- not two -- and flew with a similar construction to the Wright Brothers' Kitty Hawk plane, contends new research led by the renowned dinosaur and early avian hunter Xing Xu.
Xu, a paleontologist at the Chinese Academy of Sciences, and his team suggest this perhaps might be the simplest form of flight, as even the Wright brothers' first experiments with flight were done with a biplane in 1903.
As for how this system in birds evolved, Xu told Discovery News, "The first birds descended from four-winged dinosaurs, which are not necessarily gliders in the strictest sense."
One such dinosaur might have been Microraptor, a non-avian dino that had feathers on both its arms and legs. Paleontologists believe it could fly.
The researchers studied well-preserved fossils of 11 birds from at least four diverse groups dating from about 150 to 100 million years ago. All of the birds were found in the Jehol formation in Liaoning, northeastern China.
The ancient birds were found to have clumps of stiff leg feathers that resemble wings. Xu and his colleagues believe these were, in fact, wings, according to the study, published in the journal Science. He said they "either provided lift, or created drag, or enhanced maneuverability or a combination of all of these functions."
Xu explained that the earliest birds were primarily arboreal, so they would have flown from trees instead of taking off from the ground or water, as today’s birds often do, depending on the species.
This could help to explain why birds lost the extra “wing” leg feathers over time, evolving the two-winged anatomy of today.
Xu said that this loss happened “primarily because of the evolution of two different locomotion systems in birds -- arm wings for flight and legs for walking and running.”
He added that the shift from a tree habitat to ground and water ones would have also favored the loss of the leg feathers.
Sankar Chatterjee, a paleontologist at Texas Tech University, told Michael Balter of Science that the new study makes it clear that "the four-wing form was exhibited not just by Microraptor, but also retained in successive lineages of early birds."
Kevin Padian, a paleontologist at the University of California at Berkeley, also agrees that the research establishes that leg feathers were widely distributed, but he remains skeptical that the leg feathers were, in fact, used for flight.
"No one thinks that these animals flapped their legs, so what is the argument about improving flight?" he asked, adding that "no one has performed any kind of adequate functional or aerodynamic test."
Future biomechanical studies might be on the horizon. For now, though, Xu and his team are analyzing thousands of specimens at the Shandong Museum. They believe that evidence from more fossils could help to answer some of the still-existing questions about avian evolution.