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Of special importance is his repeated demand that not only individual parts of the animals but the whole organism as well should be derived from the earlier forms. Very similar to this is the case of the "family history of birds," which as all know, has been traced back to reptiles. It is in this matter that the famous Archaeopteryx plays an important part.
The Archaeopteryx differs from all known birds, not only in the structure of its tail, but in having two, if not three, digits in the hand; but there is no trace of the fifth digit of the winged reptile.
But a reptile about two feet long, called Compsognathus, lately found in the Stonesfield slate, makes a much greater approximation to the class Aves than any Dinosaur, and therefore forms a closer link between the classes Aves and Reptilia than does the Archaeopteryx.
The possibility of going elsewhere potentially out of the reach of America's long shadow made her soar as invincibly as an archaeopteryx departing from a tyrannosaurus, if indeed these two creatures were coeval. Like a massive billowing wave of dark cloud overtaking the top stories of a skyscraper, the prospect of opaque drama in unknown foreign adventures animated her lofty imagination.
Throughout the Jurassic and Cretaceous the remains of birds are far less common than those of flying reptiles, and strata representing hundreds of thousands of years intervene between Archaeopteryx and the next birds of which we know, whose skeletons occur in the Cretaceous beds of western Kansas.
What their number may have been is uncertain; but several, if not all, of them were terminated by strong curved claws, not like such as are sometimes found in birds, but such as reptiles possess; so that, in the Archaeopteryx, we have an animal which, to a certain extent, occupies a midway place between a bird and a reptile.
It is clear that one of the smaller reptiles the Archaeopteryx is between a pigeon and a crow in size of the Triassic period was the ancestor of the birds. Its most conspicuous distinction was that it developed a coat of feathers.
In the Archaeopteryx, the upper-arm bone is like that of a bird; and the two bones of the forearm are more or less like those of a bird, but the fingers are not bound together they are free.
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