Microraptor gui: Bird or  Dinosaur

A look into the therapod dinosaur-bird evolution debate

Justin Costa Rica

                                    There are many hypotheses about the relationship between therapod dinosaurs and the birds. The most widely accepted hypothesis on the origin of birds is that birds evolved from a group of therapods called maniraptorians. Within the last decade, the line between what is a dinosaur and what is a bird has been blurred. An accumulation of new discoveries has opened a Pandora’s box of debate over the origin of birds. The recent discovery of Microraptor gui (Fig. 1), presumably a feathered dinosaur, has added fuel to the fire of what characters define a bird. Microraptor gui was discovered in the Jiufotang Formation in western Liaoning, China. Microraptor gui is 77 cm in length and has four wings. The feature that makes Microraptor gui unique is that it has a wing on each hind-limb. At first glance, one would think that Microraptor gui would be a bird. The evidence supporting Microraptor gui being a bird is that feathers are present covering the whole body, and its forelimbs are modified for flight. However, the evidence supporting Microraptor gui being a dinosaur is overwhelming. Microraptor gui has a digit pattern of 1-2-3, rather than the 2-3-4, seen in birds and possesses the “killer” claw which is characteristic in most basal dromaeosaurs. The next question is the phylogenetic position of Microraptor gui (Fig. 2). Xing Xu proposes that Microraptor gui is part of a tetrapteryx stage of evolution. In 1915, William Beebe proposed that the first bird would be a four-winged glider. Evidence for Beebe’s hypothesis comes from the asymmetrical feather vanes that indicate an aerodynamic morphology for flying. Because of the importance of the specimen to the origin of birds, paleoornithologists like Allan Feduccia question whether the fossil is a forgery like Archeoraptor was demonstrated to be. Further study is needed on Microraptor gui, and similar specimens, to better understand the origin of birds and the beginning of flight.

Figure 1 A reconstruction of M. gui showing the morphology  and distribution of the pennaceous feathers. Nature Vol. 421, page 336, January 23, 2003.

Figure 2 The origin of birds within therapod dinosaurs. Nature Vol. 421, page 323, January 23,2003

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