Much to the dismay of the BADs (Birds Are Dinosaurs), there is a group of scientists who are in denial of the thesis that theropod dinosaurs evolved into birds. Furthermore, this BAND of scholars (Birds Are Not Dinosaurs) have published in the esteemed PNAS and not in some obscure low-ranked journal. The research was concerned with the dromaeosaurid Microraptor gui, which was first described in 2002 and has flight feathers on all four limbs. The research team modelled M. gui flight and concluded that gliding was its forte.
"We suggest that Microraptor was an adept glider and would have had little difficulty gliding from tree trunk to tree trunk or climbing trees, but would have been very awkward and vulnerable on the ground. The primary feathers on the tarsometatarsus (foot) of the hindwing of M. gui were too long in relation to the limb bones to have allowed the hindwing to fold compactly as does the modern bird wing. Just as colugos and sloths have their limbs encumbered by patagia, the hindwing feathers on Microraptor would severely hamper any terrestrial locomotion."
John Ruben draws attention to an image drawn in 1915 by naturalist William Beebe. It suggests a hypothetical view of what early birds may have looked like, gliding down from trees - and it bears a striking similarity to a fossil discovered in 2003 that is raising new doubts about whether birds descended from ground-dwelling theropod dinosaurs (Source here)
In an accompanying commentary, John Ruben reviewed the history of the controversy over the origins of bird flight. Much to the disapproval of the BADs, Ruben presents those skeptical of the cursorial, ground-upwards hypothesis as scholars who have championed reasoning from evidence. The new research, Ruben suggests, favours gliding, arboreal proto-birds. But he also suggests that some more radical thinking may be warranted:
"So, is the answer, after all, a hybrid of the two old theories, i.e., avian origins from an arboreal, gliding theropod dinosaur? Perhaps, but then this is paleobiology - very recent data suggest that many clearly cursorial theropods previously thought to have been feathered may not have been so and that dromaeosaurs, the group that birds are assumed to have been derived from, may not even have been dinosaurs. What pops up next is anyone's guess."
The Science Daily report points to these more fundamental divergences of view:
The weight of the evidence is now suggesting that not only did birds not descend from dinosaurs, Ruben said, but that some species now believed to be dinosaurs may have descended from birds.
"We're finally breaking out of the conventional wisdom of the last 20 years, which insisted that birds evolved from dinosaurs and that the debate is all over and done with," Ruben said. "This issue isn't resolved at all. There are just too many inconsistencies with the idea that birds had dinosaur ancestors, and this newest study adds to that."
Breaking out of the conventional wisdom? Yes - we need some more of that!
Paleobiology and the origins of avian flight
Proceedings of the National Academy of Sciences, published online before print February 9, 2010 | doi:10.1073/pnas.0915099107
First sentence: Interpreting the paleobiology of long extinct taxa, pesky new fossils, and reinterpretations of well-known fossils, sharply at odds with conventional wisdom never seem to cease popping up.
Model tests of gliding with different hindwing configurations in the four-winged dromaeosaurid Microraptor gui
David E. Alexander, Enpu Gong, Larry D. Martin, David A. Burnham, and Amanda R. Falk
Proceedings of the National Academy of Sciences, Published online before print January 25, 2010 | doi: 10.1073/pnas.0911852107
Abstract: Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbs functioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphology or likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. [. . .] Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui's feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.
Bird-from-Dinosaur Theory of Evolution Challenged: Was It the Other Way Around?, ScienceDaily (Feb. 10, 2010)
Deyes, R. B.A.R.B: Birds Are Really.....Birds!, ARN Literature Blog (25 June 2009)
Tyler, D. Did birds fly in the Late Triassic? ARN Literature Blog (16 June 2009)
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