Untitled more than a slight keel, if any, on the breast-bone, it is unlikely that they could fly far. For we know from our modern birds that the power of flight may be to some extent gauged from the degree of development of the keel, which is simply a great ridge for the better insertion of the muscles of flight. It is absent, of course, in the Running Birds, like the ostrich, and it has degenerated in an interesting way in the burrowing parrot (_Stringops_) and a few other birds that have "gone back." The First Known Bird But the Jurassic is particularly memorable because its strata have yielded two fine specimens of the first known bird, _Arch±opteryx_. These were entombed in the deposits which formed the fine-grained lithographic stones of Bavaria, and practically every bone in the body is preserved except the breast-bone. Even the feathers have left their marks with distinctness. This oldest known bird--too far advanced to be the first bird--was about the size of a crow and was probably of
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