Microraptor Gui: The Dinosaur with Four Wings
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Knowing that pterodactyls belong to a separate group of reptiles than dinosaurs, the thought of a dinosaur with wings may seem somewhat strange. But a fairly recent archeological find adds an extra detail to make this idea truly bizarre: a dinosaur with four wings. Microraptor gui, discovered by Xing Xu and colleagues, is believed to be a kind of missing link between strictly ground-dwelling dinosaurs and birds, namely Archaeopteryx, the earliest known creature to be considered a bird. While there can be no debate over the discovery itself, the implications made from its discovery haven’t been entirely accepted, with many arguing them altogether. Besides being an oddity, what makes this particular find so significant? What are these implications that have riled some scientists up, and what is it that these experts argue?
Before any sort of discussion on the debate of what M. gui implies, however, the details of this odd reptile’s discovered fossils should be given. Through past research and findings, the leading theory on the origin of birds traces them back to dinosaurs, more specifically a type of bipedal dinosaur called theropods. Within this group of mostly carnivorous dinosaurs are the dromaeosaurids, and they specifically are believed to be the closest dinosaur ancestors of birds.
The discovered fossils of the dramaeosaurid M. gui form of a nearly complete skeleton, and it’s been compared with a similar, previously discovered Microraptor skeleton. The place of M. gui’s discovery was Dapingfang, Chaoyang County in western Liaoning, China, also known as the Jiufotang Formation_. Xu and colleagues declare the fossils to be dated from the early Cretaceous period (about 124 - 128 million years ago_)_ through others’ radiometric dating and biostratagraphical correlations of that region_. Interestingly, the closest ancestors of many of the dinosaurs found within this area of China are believed to have lived not during the early Cretaceous, but the late Jurassic_. Paleogeographers have theorized that this area was thoroughly isolated during the very late Jurassic and into the early Cretaceous_. With paleontologists theorizing that Archaeopteryx came into existence 25 million years before the dated existence of these M. gui fossils_, M. gui is still believed to be a basal dromaeosaurid, meaning that it’s one of the earliest of this type of theropod, maintaining that these fossils are of an ancestor to Archaeopteryx and all birds.
The actual skeleton of M. gui shows that it’s total length, including its long tail, is about 77cm, making it a fairly small dinosaur_. Obviously there are other qualities to this fossil that make it truly unique, though. Firstly, along its arms are the traces of feathers, and when compared to the feathers of Archaeopteryx are seen to be of the same formation_. This formation also happens to be the same of the wings on today’s birds, and shows that this particular feather formation allows flight_. Secondly, the legs have running almost entirely along them the same kind of feather formations as the arms, meaning that these too were functioning wings_. Along with a feathered tail, Xu and colleagues have justly surmised that M. gui was capable of some form of aerial flight.
The discoverers go further than that with their implications, though. With the four wing setup of this dinosaur, they theorize that M. gui was not an actual flyer, but a glider_. Comparisons to the modern day flying squirrel_ help to conceptualize the capabilities of this odd reptile. In fact, Xu and colleagues imply even more similarity to this currently existing mammal by saying that M. gui lived in the trees_. With the feathers running along so much of M. gui’s legs, they believe that the dinosaur likely couldn’t walk along the ground, or at least couldn’t walk very fast_. This is combined with other research that’s recently tied the feet of more closely bird-related theropods and basal birds to basic arboreal functioning (meaning the feet were adapted for scaling and walking along trees)_. With all of this, Xu and colleagues theorize that M. gui, and all basal dromaeosaurids, were arboreal_. In other words, the discoverers have theorized that these ancestors of birds lived in the trees, using their four-winged bodies to glide from branch to branch, and that later on in time the descendants lost these back feathers, yielding birds, which use only their two front limbs for flight_.
To many this answers a question that’s existed for quite some time now: how did birds become capable of flight? There have been two competing answers to this question, the first of which is that the evolution toward a flying creature began with organisms that lived in the trees, developing ways to glide from tree to tree, and that eventually these organisms developed the ability to not only glide, but to propel themselves upward on their own_. The other is that fast-running bipedal dinosaurs developed wings and could eventually take off due to their capability of such speed_.
Showing how long this debate has existed, in 1915, some time after the discovery of Archaeopteryx, the naturalist_ William Beebe proposed that the flight of birds first evolved with a hypothetical, tree-dwelling “tetrapteryx” that glided with the use of four wings (which is exactly what M. gui is)_. As Richard O. Prum explains, this theory’s, “been supported by the observation that flight is energetically more efficient at higher speeds (when more lift is generated)”_. He further explains this support by noting that when gliding, “the flight stroke is continuous, [so] level flight is simpler than in take-off from the ground”_. There’s more support with the fact that many organisms that live today and in trees, like frogs, snakes, and lizards, have developed their own gliding methods_.
Not everyone seems to believe all of this. Why, exactly? Some believe that the theory competing with the idea of arboreal, gliding descendants of birds, is more likely to be true. This theory originated when it was first theorized with good evidence that the bipedal theropods were the descendants of birds_. For some time it’s been believed that all theropods were terrestrial, and so came the idea of a reptile with winged arms that could run fast enough to actually take off_. But there’s also the fact that models of Archaeopteryx’s aerodynamics included wings that, along with quick legs, could gain enough speed for a take-off_. Evidence of contemporary birds exists that supports this theory as well. Somewhat recently, scientists found that chicks can evade danger even before learning to fly, and the support for the terrestrial theory is in their method of dodging a threat_. They save themselves from harm by running toward a tree with their tiny, undeveloped wings flapping so that the speed and lift power are enough to take them up the tree to safety_.
Others that don’t believe in the implications of the discovered M. gui do so because they simply don’t see enough evidence in the fossils found by Xu and colleagues to make the discoverers’ theories very believable_. The paleontologist James Clark describes the need for caution in an article by Hillary Mayell by saying, “interpreting function from a fossil is highly speculative . . . there’s just a lot we aren’t going to know”_. Some believe that the whole debate is simply too oversimplified to have as clear an answer as what either theory suggests, and that there’s really no way to test them_.
It does seem that the discovery of M. gui doesn’t make some ideas as clear as Xu et al and others believe. For example, how did M. gui use its wings_? Is it entirely ruled out that it didn’t propel itself_? Part of what makes dinosaurs dinosaurs is the fact that their legs are positioned underneath them, so is it really possible that this four-winged dinosaur could’ve positioned all of its limbs for any sort of flight_? Certainly scientists will look more closely at the anatomy of M. gui, in particular the hips and legs, to answer these questions. Also, with these theories saying that dromaeosaurids lost their hind wings before some of them eventually lead to the evolution of Archaeopteryx, the question comes up of whether or not this first bird also had four wings, or if this characteristic belongs only to dromaeosaurid.
These questions will have to wait to be answered, unfortunately. Only with the further working and searching of paleontologists and other scientists can these answers be found. Certainly more and more knowledge and understanding will be accumulated as efforts progress, just as the list of reptilian oddities of millions of years ago increases with further discoveries. If dinosaurs seem varied and strange now, who knows how bizarre our idea of them will be in the future?
_ Xu, X. et al. “Four Winged Dinosaurs from China.” Nature. 421 (2003): 335-340.
_ Prum, Richard O. “Paleontology: Dinosaurs Take to the Air.” Nature. 421 (2003): 323-324.
_ Zhou, Z. et al. “An Exceptionally Preserved Lower Cretaceous System.” Nature. 421 (2003): 807 - 814.
_ Mayell, Hillary. “Four-Winged Dinosaurs Found in China, Experts Announce.” National Geographic News. 22 January 2003. April 4 2003. <http://news.nationalgeographic.com/news/2003/01/0121_030122_dromaeosaur.html>.
_ Gee, Henry. “Fossil Boosts Tree-Down Start for Flight.” Nature News Service. 23 January 2003. April 4 2003. <http://www.nature.com/nsu/030120/0301207.html>.