Popular Science Monthly
��Vol. 91 No. 1
��239 Fourth Avenue, New York City
��A Bird with Four Wings
When Nature decided to evolve a bird out of a reptile she molded a four-winged flyer curiously like the first flying machine
By Maurice Krosby
��BIRDS came later than fishes and reptiles in the evolution of life. But what manner of creature was it that linked fish with bird? What was the first
��bird that ever fl(
��mains and imprints have so far given only scant information as to how the feathered de- scendants of the fish or the rep- tile gradually came into posses- sion of the power of flight. Intermediate links in the develop- ment have left but few and faint traces, and this is due, at least in part, to the extreme remoteness of the transition period durin which birds became birds from whatever they were before. The change was so radical that it re- quired millions of years by Na- ture's slow methods.
Fortunately a single natural document has come down through the ages which goes far toward explaining the mechanics that made the elongated swimming fish or crawling reptile fit for sustaining, propelling and balancing it- self in the air, and this document, as it happens, also establishes a most curious and interesting parallel between Nature's experiments in flying and those funda- mental experiments by Professor Langley of the Smithsonian Institution in Washing- ton to which the inauguration of the air- plane era in flight is due, more than to any other one cause. The document referred to is a true document; for it was found printed by natural forces on the rocks of the Solinghofen quarry in Germany. Here, in a formation not less than seven million years old, one of the ancestors of the
���This is Nature's first attempt at creating a flyer
��modern bird, a strange feathered reptile, had been imprisoned, caught unawares per- haps in one of the every-day upheavals of that formative age when mountain ranges, continents and oceans were still in the making. Its skeleton, its outlines and its feathers are here preserved, stamped in un- mistakabledistinctnessin stone, which is now hard but which must have been plastic as clay when the fluttering creature was seized in deadly embrace. More than twice as old as any of the prehistoric monsters reconstructed from their bones in our museums of natural history, the fossil im- print of the Tetrapteryx, as this creature has been named (mean- ing "four-winger"), represents an indisputable and descriptive rec- ord of perhaps the earliest feath- ered flyer.
The Tetrapteryx record was discovered fifty-five years ago, but science has only re- cently undertaken to interpret it mechani- cally. William C. Beebe, while curator of birds at the New York Zoological Park, demonstrated that several species of modern birds, and especially the white-winged dove, show very marked traces of just such wings on the legs, called pelvic wings, as the Tet- rapteryx record reveals. On the very young dove, at the time when its body is still bare but for the sprouting flight feathers of wings and tail, twelve flight feathers and six coverts begin to grow from the outer and upper edge of the leg, extending in two rows from the knee almost to the base of the tail. While the growth of these tell-tale feathers is soon arrested and is covered up