The bird fossil was named for having been discovered in the famous Messel shales. None of the bodily mechanisms of birds, which have a completely different structure from terrestrial life forms, can be explained in terms of any gradual evolutionary model. First of all, wings—the most important feature that makes birds what they are—represent a complete impasse for the theory of evolution. Evolutionists themselves state the impossibility of a reptile being able to fly and indeed, that this claim is contradicted by the fossil record. The ornithologist Alan Feduccia, for example, asks, "How do you derive birds from a heavy, earthbound, bipedal reptile that has a deep body, a heavy balancing tail, and fore-shortened forelimbs? Biophysically, it's impossible." ("Jurassic Bird Challenges Origin Theories," Geotimes, January 1996, p. 7.) The fossilization of birds is generally a very rare and difficult process because of the hollow structure of their bones. Bird fossils that are very well-preserved with all their limbs are frequently encountered, however, in the Messel Formation in Germany. Messelornis cristata, shown here, is one of the species most frequently discovered. This bird, resembling a small crane in size, is generally included as part of the crane family. It has short feathers, long legs and short nails. Its tail feathers, on the other hand, are quite long. The crest on its head resembles a helmet. The total length of the skeleton is 25 to 30 centimeters (9.8 to 11.8 in).