Monday, January 22, 2007
From the Washington Post: When the Wright Brothers first took to the sky in a biplane, they were using a design nature may have tried 125 million years earlier. A new study of one of the earliest feathered dinosaurs suggests it may have had upper and lower sets of wings, much like the biplanes of early aviation. Today, the biplane is widely considered an old-fashioned rarity.
And the design is no longer seen in birds, though it's not clear if it was a step on the way to modern birds or a dead end, tested by nature and discarded.
The intriguing possibility of a biplane dinosaur Microraptor gui is suggested by Sankar Chatterjee of Texas Tech University in this week's online issue of Proceedings of the National Academy of Sciences.
Continued at "Dinosaur May Have Resembled the Biplane"
Based on the open access PNAS paper:
Sankar Chatterjee and R. Jack Templin
Biplane wing planform and flight performance of the feathered dinosaur Microraptor gui
PNAS published January 22, 2007, 10.1073/pnas.0609975104
Microraptor gui, a four-winged dromaeosaur from the Early Cretaceous of China, provides strong evidence for an arboreal-gliding origin of avian flight. It possessed asymmetric flight feathers not only on the manus but also on the pes. A previously published reconstruction shows that the hindwing of Microraptor supported by a laterally extended leg would have formed a second pair of wings in tetrapteryx fashion. However, this wing design conflicts with known theropod limb joints that entail a parasagittal posture of the hindlimb. Here, we offer an alternative planform of the hindwing of Microraptor that is concordant with its feather orientation for producing lift and normal theropod hindlimb posture. In this reconstruction, the wings of Microraptor could have resembled a staggered biplane configuration during flight, where the forewing formed the dorsal wing and the metatarsal wing formed the ventral one. The contour feathers on the tibia were positioned posteriorly, oriented in a vertical plane for streamlining that would reduce the drag considerably. Leg feathers are present in many fossil dromaeosaurs, early birds, and living raptors, and they play an important role in flight during catching and carrying prey. A computer simulation of the flight performance of Microraptor suggests that its biplane wings were adapted for undulatory "phugoid" gliding between trees, where the horizontal feathered tail offered additional lift and stability and controlled pitch. Like the Wright 1903 Flyer, Microraptor, a gliding relative of early birds, took to the air with two sets of wings.
The evolution of powered flight in birds from theropod dinosaurs is recognized as the key adaptive breakthrough that contributed to the biological success of this group. The transformation of wing design from nonavian dinosaurs to early birds is beginning to unravel in recent times from a wealth of fossil record from China. Hundreds of small, exquisitely preserved, feathered theropods were discovered in the Early Cretaceous Jehol Group of northeastern China as they died some 125 million years ago, smothered in the "Cretaceous Pompeii." Both anatomy and phylogeny strongly suggest that these theropods, including Sinosauropteryx, Caudipteryx and Protarchaeopteryx, Microraptor, Sinornithosaurus, Cryptovolans, and the early bird Confuciusornis, show constructions ranging from small winged, arboreal theropods to fully winged, active flying birds. They offer new insights into the origins of feathers and flight, favoring the arboreal ("trees-down") over the cursorial ("ground-up") hypothesis. Among these recent finds, Microraptor gui offers the best evidence that arboreal dromaeosaurs might have acquired powered flight through a gliding stage where both forelimbs and hindlimbs were involved.
Sankar Chatterjee also presented a paper on the Microraptor gui at the Geological Society of America - 2005 Annual Meeting in Salt lake City, Utah. The press release below (relevant to the foregoing PNAS paper) is followed by a link to an abstract of the paper Chatterjee presented:
Wright Brothers Upstaged! Dinos Invented Biplanes
The evolution of airplanes from the Wright Brothers' first biplanes to monoplanes was an inadvertent replay of the much earlier evolution of dinosaur flight, say two dino flight experts.
According to paleontologist Sankar Chatterjee and retired aeronautical engineer R.J. Templin, a small early Chinese dinosaur called Microraptor gui used a two-level, biplane wing configuration to fly from tree to tree in the early Cretaceous. Among the evidence for the early biplane is that Microraptor had unmistakable flight feathers on its hind limbs as well as on its wings, says Chatterjee, a distinguished professor at Texas Tech University in Lubbock. The Chinese paleontologists who first reconstructed Microraptor had guessed that its four wings were used in tandem, similar to those of dragonfly.
Chatterjee will present the new biplane flight findings at 4 p.m. MDT on Sunday, 16 October (2005), at the Annual Meeting of the Geological Society of America in Salt Lake City.
"The most unusual thing is that they have flight feathers not only on the hand section, but also on foot," said Chatterjee. Flight feathers differ noticeably from other feathers in that they are asymmetrical with interlocking barbules to keep their shape. The leading edge of each long feather was narrower than the trailing edge, which helped streamline the body in flight. The hooked, interlocking barbs gave strength and flexibility to the feather and prevented air from passing through it in flight.
Some present-day birds, especially raptors as well as the earliest Jurassic bird Archaeopteryx, also have (or had) feathers on their legs, Chatterjee says. But these are not flight feathers and appear adapted to streamline the legs during catching and carrying prey so they don't interfere with flight.
Another key element to discovering Microraptor's flight secrets was setting some realistic limitations on how the dinosaur could move its hindlimbs - something that was initially overlooked by Chinese researchers who found the fossil. Chatterjee and Templin studied its anatomy and found that like any dinosaurs, Microraptor held their hindlimbs in erect, vertical plane, permitting forward and backward motion.
"The problem we faced is that the legs of Microraptor, like on any dinosaur, could not be splayed sideways," as the Chinese paleontologists assumed. That means Microraptor could not have extended its rear limbs to form a wing directly behind the front wing. More likely, and more aerodynamically stable, would have been a rear wing that was held lower than the front wing - what from the side would look like a staggered biplane configuration, Chatterjee explains.
Chatterjee and Templin fed Microraptor's flight data into a computer simulation that they have previously used to successfully analyze the flying abilities of pterosaurs and Archaeopteryx. Based on the aeronautical analysis, it appears that Microraptor flights looked rather like those seen today among some "monoplane" forest birds - something called undulating phugoid gliding, Chatterjee said. In other words, Microraptor launched from a high branch and dove off, falling head-first until it reached a speed that created lift on its wings. With that lift the feathered dino then swooped upwards and landed in the branches of another tree without having to flap its wings and expend muscular energy.
"The biplane wing configuration was probably a very first experiment in nature," says Chatterjee of the early flying technique, which was also used by another feathered dinosaur from China, Pedopenna, he said. Archaeopteryx achieved fully powered flight with monoplane configuration, as its wing became even larger than those of Microraptor, but foot feathers were lost.
"It is intriguing to contemplate that perhaps avian flight, like aircraft evolution, went through a biplane stage before the monoplane was introduced, said Chatterjee. "It seems likely that Microraptor invented the biplane 125 million years before the Wright 1903 Flyer."
The discovery of Microraptor and other small, exquisitely preserved feathered dinosaurs from China also helps to settle a century-old controversy over whether avian flight began in trees (trees-down theory) or on the ground (ground-up theory). These fossils show various transitional stages-from wingless, tree-dwelling theropod dinosaurs to fully winged, active flyers, Chatterjee said.
The central theme of the trees-down theory is that gravity was the source of energy: a small climbing dinosaur first parachuted down, then began to stay aloft longer by gliding, and finally acquired powered flight. As those abilities developed, feathers became larger and more specialized, providing greater lift and thrust. The Chinese feathered dinosaurs show these transitional stages of flight.
In contrast, the ground-up theory has a theropod struggling toward flight directly from the ground, against gravity, without any gliding stage. Such long feathers around the feet would make it hard for Microraptor to run on the ground, says Chatterjee, supporting the idea that it was a tree dweller, thus reinforcing the trees-down theory.
Based on the presentation "The Feathered Dinosaur Microraptor: Its Biplane Wing Planform and Flight performance"
Sankar Chatterjee co-authored the 2003 Letter to Nature "Neuroanatomy of flying reptiles and implications for flight, posture and behaviour" (doi: 10.1038/nature02048):
Comparison of birds and pterosaurs, the two archosaurian flyers, sheds light on adaptation to an aerial lifestyle. The neurological basis of control holds particular interest in that flight demands on sensory integration, equilibrium, and muscular coordination are acute. Here we compare the brain and vestibular apparatus in two pterosaurs based on high-resolution computed tomographic (CT) scans from which we constructed digital endocasts. Although general neural organization resembles birds, pterosaurs had smaller brains relative to body mass than do birds. This difference probably has more to do with phylogeny than flight, in that birds evolved from nonavian theropods that had already established trends for greater encephalization. Orientation of the osseous labyrinth relative to the long axis of the skull was different in these two pterosaur species, suggesting very different head postures and reflecting differing behaviours. Their enlarged semicircular canals reflect a highly refined organ of equilibrium, which is concordant with pterosaurs being visually based, aerial predators. Their enormous cerebellar floccular lobes may suggest neural integration of extensive sensory information from the wing, further enhancing eye- and neck-based reflex mechanisms for stabilizing gaze.
Sankar Chatterjee is author of the book "The Rise of Birds: 225 Million Years of Evolution":
Among the Dockum fossil beds of West Texas in 1983, paleontologist Sankar Chatterjee made a momentous discovery: the fossilized remains of a curious creature subsequently dubbed Protoavis, or primordial bird. In The Rise of Birds, Chatterjee writes that Protoavis predates Archaeopteryx, previously known as the "first bird" by some 75 million years, and that it is more closely related to the modern bird than its Johnny-come-lately rival. But Protoavis is only the starting point for this sweeping, detailed, and beautifully illustrated history of bird evolution. Chatterjee examines the many recent discoveries of bird fossils all over the world and comes to some fascinating and often surprising conclusions: the evolutionary link between birds and dinosaurs, for instance, or their near-extinction (along with the dinosaurs) when large meteors fell to earth almost 65 million years ago. From the distinguishing characteristics of avian anatomy to theories about the first avian flight, Chatterjee's book is a thoughtful and accessible look at one of the most flourishing products of evolution. (Amazon Astore - links below)
In 2003 National Geographic wrote in the article "Four-Winged Dinosaurs Found in China, Experts Announce":
"Paleontologists in China have discovered the fossil remains of a four-winged dinosaur with fully developed, modern feathers on both the forelimbs and hind limbs.
The new species, Microraptor gui, provides yet more evidence that birds evolved from dinosaurs, and could go a long way to answering a question scientists have puzzled over for close to 100 years: How did a group of ground-dwelling flightless dinosaurs evolve to a feathered animal capable of flying?"
A post from Friday, September 22, 2006:
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