The first flying vertebrates were true reptiles in which one of the fingers of the
front limbs became very elongated, providing support for a flap of stretched skin
that served as a wing. These were the pterosaurs, literally the "winged lizards." The
Lineearliest pterosaurs arose near the end of the Triassic period of the Mesozoic Era, some
(5) 70 million years before the first known fossils of true birds occur, and they presumably
dominated the skies until they were eventually displaced by birds. Like the dinosaurs,
some the pterosaurs became gigantic; the largest fossil discovered is of an individual
that had a wingspan of 50 feet or more, larger than many airplanes. These flying
reptiles had large, tooth-filled jaws, but their bodies were small and probably without
(10) the necessary powerful muscles for sustained wing movement. They must have been
expert gliders, not skillful fliers, relying on wind power for their locomotion