Second in the series, following my previous entry. I will be posting these on Sunday of each week (simply because it’s convenient) so this will be posted only a few days after the previous installment. All other installments follow each seven days from now on.
Today’s installment deals with the infamous Microraptor, a dinosaur with two sets of wings, one on the conventional arms, and another apparently on the hindlegs.
This was produced shortly after the debate began over how these wings functions, or even if they should have been called “wings,” and the term biplane  became more and more common in dealing with the wing structure. You will notice first that the two sets of wings are not the same size or shape: They are rendered after the type of Microraptor gui , and as such the material shows incomplete preservation of the feathers. The designs were rendered as half of the animal, then mirrored (with minor tweaking to make them a little less symmetrical in some regions) and with a different hindlimb drawn for model C.
At the time, it was argued by some, including in the original paper  that the hindleg was extended outwards and posteriorly. The position has been the subject of both popular scientists [1,3] and a well-made documentary  whose subject included a team intent on resolving the issue of aerodynamic precision in various postures, and which has since been published . Unfortunately, previous arguments [1,2,5] ran aground of an argument where it was claimed that the hindlimb could evert laterally at the hip, such that the femur was elevated from a parasaittal position to allow the entire leg to operate as an extended planiform, like the forelimb. This had since been rebutted on the DML , but not published, where it was shown using well-preserved specimens of Microraptor zhaoianus  that the femoral head would have had to have dislocated from the hip socket and/or the ilium to break to permit this level of eversion. Nonetheless, it is not the only way to tackle the argument , and for the most part, the most parsimonious argument seems to demonstrate that the legs were capable of some extension, not a lot, and that the feathers had an aerodynamic component, but need not have been suited for flight or gliding. Arguments for the biplane excercise are essentially predicated on the need to utilize the hindleg as an active flapping limb, and there does not seem to be any evidence that this was accurate.
 Paul, G. S. 2003. Screaming biplane dromaeosaurs of the air. Prehistoric Times 60:48-50.
 Xu X., Zhou Z.-j., Wang X.-l., Kuang X., Zhang F.-c. & Du, X. 2003. Four-winged dinosaurs from China. Nature 421:335-340.
 Chatterjee, S. & Templin, R. J. 2007. Biplane wing platform and flight performance of the feathered dinosaur Microraptor gui. Proceedings of the National Academy of Sciences, Philadelphia 104(5):1576-1580.
 Paul, G. S. 1988. Predatory Dinosaurs of the World. (Simon & Schuster, New York City)
 Nova 2008. The Four-Winged Dinosaur. PBS Program link
 Alexander, D. E., Gong E., Martin, L. D., Burnham, D. A. & Falk, A. R. 2010. Model tests of gliding with different hindwing configurations in the four-winged dromaeosaurid Microraptor gui. Proceedings of the National Academy of Sciences, Philadelpha 107(7):2972-2976.
 Hartman, S. 2004. Microraptor did not sprawl! Dinosaur Mailing List, April: Link
 Hwang, S. H., Norell, M. A., Ji Q. & Gao K.-q. 2002. New specimens of Microraptor zhaoianus (Theropoda: Dromaeosauridae) from northeastern China. American Museum Novitates 3381:1-44.