|Evolution in the News - March 2003|
|by Do-While Jones|
There was a lot of publicity lately about Microrapter gui, popularly called the “four-winged feathered dinosaur”. What does it teach us about the origin of flight?
The diminutive dinosaurs, described in the current issue of Nature, are dromeosaurs, the group that the majority of paleontologists thinks is most closely related to birds. All six belong to a small club called the microraptors, and one is a member of a new species, Microraptor gui. A team led by Xing Xu and Zhonghe Zhou of the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing collected one of the new specimens in 2001 in Liaoning Province, and the group purchased five others that came from the same area.
Zhou argues that microraptors lived in trees (Science, 8 December 2000, p.1871). Part of what makes that plausible is their small size: M. gui's trunk is roughly 15 cm long.
The feathers of the six animals are arranged for the most part like those of modern birds. The body is covered with downy feathers, the tail has a tuft of longer ones, and the hands each have about a dozen flightlike "primary" feathers. Along the front limb are 18 or so shorter, "secondary" feathers. The hind limbs sport the same pattern of plumage, confirming a hint published last year when another team found a dromeosaur with a single hind-limb feather. 1
There is no doubt that this creature existed. Whether it was a bird, dinosaur, or something else, was discussed in our feature article. In this column we want to consider what we can learn from the existence of this creature.
Some people claim M. gui tells us something about the origin of flight. They think that this creature was not able to fly, but could glide at least as well as a flying squirrel. This confirms their belief (which they already held, without any evidence) that the first birds were gliders. Later birds, they think, learned to flap their wings and fly better. Here is what they say:
For more than a century, debate on the origin of bird flight has centred on two different hypotheses. According to arboreal theories, flight arose in tree-dwelling creatures through an intermediate gliding stage, an idea that has been supported by the observation that flight is energetically more efficient at higher speeds (when more lift is generated). Further, the flight stroke in continuous, level flight is simpler than in take-off from the ground. According to the competing, cursorial theories, flight evolved in ground-living animals via a powered running stage. This view is supported by the evidence that birds evolved from a lineage of terrestrial, bipedal theropods, and that many components of the avian flight apparatus evolved originally in a terrestrial context. Moreover, aerodynamic models of the flight stroke of Archaeopteryx, the earliest bird accepted as such, indicate that its wings could have provided thrust as well as lift, and aided the legs in achieving enough ground speed for a running take-off.
In a colourful and prescient paper of 1915, however, William Beebe proposed that avian flight evolved through a gliding, four-winged--tetrapteryx--stage with wing feathers on both the arms and the legs. Now Xu and colleagues describe a small dromaeosaur, Microraptor gui, that sports four wings of fully modern, asymmetrical feathers on its forelimbs and legs, and looks as if it could have glided straight out of the pages of Beebe's notebooks. Although the specimens of Microraptor are younger than those of Archaeopteryx, Microraptor is a basal member--an early evolutionary branch--of the closest relatives of Archaeopteryx and other birds. In support of the arboreal theory, Xu et al. propose that the most recent common ancestor of birds and dromaeosaurs was a four-winged creature that lived in and glided among trees. 2
But there are some problems.
The discovery of a logical functional intermediate provides striking support for the arboreal-gliding hypothesis of the origin of bird flight. However, substantial questions remain. In particular, how did Microraptor actually use its four wings? Perhaps because flapping hindwings are so unlikely, Xu et al. conclude that Microraptor merely glided, and did not have a powered flight stroke. Palaeontologists and functional morphologists will be eager to study the shoulder and wing anatomy to judge whether Microraptor could sustain powered flight. More information is also required on how the animal could have rotated its legs to deploy its hindwings. 3
Xu et al. also argue that the extensively feathered legs of Microraptor would have been incompatible with life on the ground. The feathers extend all the way down the leg, much further than they do in Beebe's mythical tetrapteryx. Dragging your wing feathers in the dirt would doubtless be aerodynamically disadvantageous, but it will require detailed reconstructions of Microraptor's hindlimbs with feathers attached to rule out the possibility that it could have walked and run. 4
In addition, the rear feathers would have tripped up a cursorial, or running, dinosaur, they argue--making it unlikely that the creatures used a running start to evolve flight. (Other recent evidence, however, favors such a ground-up scenario; see Science, 17 January, p.329.) 5
In other words, your shoulders are constructed in such a way that you can stretch your arms straight out from your side. You can flap your arms like wings. But your hips are constructed in such a way that you can’t stick your legs out to the side and flap them. M. gui could not do that, either.
Furthermore, the feathers on the hind legs would make it very difficult to walk or run. (The “evidence” favoring the ground-up scenario in the 17 January issue of Science is based on observations of modern chickens and similar birds flapping their wings as they run uphill.)
We haven’t seen any literature suggest that M. gui could have been an extinct aquatic bird capable of swimming under water (like an Anhinga or Cormorant). We suspect that this is because many people want to know how birds learned to fly, but few care about how birds learned to swim. According to the old proverb, “When the only tool you have is a hammer, every problem looks like a nail.” When you are looking for a dinosaur that was learning to fly, every fossil with feathers looks like a dinosaur learning to fly, even if it is an aquatic bird.
Evolutionists recognize, but gloss over, the real problem. There was an allusion to it in a previous quote. Here it is explicitly stated.
Dated at about 126 million years old--some 25 million years younger than the oldest known bird, Archaeopteryx, the Chinese microraptors were not themselves the ancestors of birds. But earlier gliding dinosaurs could have been an evolutionary step from flightless dinosaurs to airborne birds, which would have eventually lost the rear wings, Zhou and Xu say. 6
M. gui (they believe) lived 126 million years ago. But Archaeopteryx, a true bird capable of powered flight, lived (they believe) about 151 million years ago. Birds had been flying (according to their belief) for 25 million years before M. gui started to glide. So M. gui can’t be the missing link between dinosaurs and birds. Birds already existed. Birds could already fly.
One could argue that the fossils we have found of Archaeopteryx are fossils of some of the first individuals of that species, and the fossil of M. gui was the last of a dying breed that was going extinct because of competition with flying birds. So, M. gui could have lived before Archaeopteryx despite the fossil dates.
Evolutionists typically don’t try to make that argument because it is the first step down a very slippery slope. Once you start arguing that creatures existed millions of years before or after the first or last known fossil, you are basically arguing that the fossil dates don’t mean anything. Creatures could have lived at any time. If fossil dates are unreliable, then you can’t use them to show evolutionary development. That isn’t a principle that evolutionists want to establish. So, they use this argument instead:
Xu et al. maintain that all four wings were present in the earliest ancestors of birds and dromaeosaurs, and that with the evolution of powered flight the hindwings were lost in the avian lineage before the advent of Archaeopteryx. 7
In other words, M. gui and Archaeopteryx must both be descendants of another creature very much like M. gui (for which nobody has ever found any fossil evidence). The undiscovered ancestor of M. gui evolved rear wings because they gave the creature some survival advantage. Then Archaeopteryx lost its rear wings to gain a survival advantage; but M. gui was still stuck with them because it didn’t evolve as much.
Here is yet another example of evolutionary circular logic. Try to follow the twisted reasoning of the evolutionists, and you will see that it comes full circle. Flight must have evolved through a gliding stage because M. gui and Archaeopteryx both evolved from a gliding common ancestor with feathers on all four wings (for which no fossils have yet been found). What is the evidence for this undiscovered common ancestor? How do we know what the common ancestor was like? It is very simple. Since Archaeopteryx and M. gui both evolved from it, the undiscovered ancestor must certainly have existed, and it must have had characteristics similar to both. Comparing the characteristics of Archaeopteryx and M. gui to the undiscovered ancestor, it is clear how flight must have evolved. Archaeopteryx must certainly have lost the feathers on its hind legs because Archaeopteryx doesn’t have them, and the undiscovered ancestor did. We know the undiscovered ancestor did have feathers on its hind legs because M. gui still has them, and M. gui evolved from it, too.
Of course, M. gui’s ability to fly (or glide) has significance only if one accepts this M. gui as an evolutionary link between dinosaurs and birds. If one found a fossil winged insect that dated just before the first bird in the fossil record, it would not have any bearing on how flight originated in birds because insects are not thought to be ancestors of birds. The only way M. gui’s flying ability would be relevant to the origin of flight in birds is if M. gui is an evolutionary ancestor of modern birds. So, you have to accept (by faith) evolution in general, and the evolution of dinosaurs into birds in particular, and you must accept the classification of M. gui as a dinosaur, for any of the analysis of M. gui to have any relevance to the origin of flight, or the origin of birds.
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Stokstad, Science, Vol. 299, 24 January 2003, “Four-Winged Dinos Create a Flutter” p. 491.
2 Prum, Nature Vol. 421, 23 January 2003, “Palaeontology: Dinosaurs take to the air” p 323 (Ev)
5 Stokstad, Science, Vol. 299, 24 January 2003, “Four-Winged Dinos Create a Flutter” p. 491.
7 Prum, Nature Vol. 421, 23 January 2003, “Palaeontology: Dinosaurs take to the air” p 323