The wing is, of course, not a feathery frame, as in
the bird, but a special skin spreading between the fore limb and
the side of the body. In the bat this skin is supported by four
elongated fingers of the hand, but in the Pterosaur the fifth (or
fourth) finger alone--which is enormously elongated and
strengthened--forms its outer frame. It is as if, in flying
experiments, a man were to have a web of silk stretching from his
arm and an extension of his little finger to the side of his
body.
From the small early specimens in the early Jurassic the flying
reptiles grow larger and larger until the time of their
extinction in the stresses of the Chalk upheaval. Small
Pterosaurs continue throughout the period, but from these
bat-like creatures we rise until we come to such dragons as the
American Pteranodon, with a stretch of twenty-two feet between
its extended wings and jaws about four feet long. There were
long-tailed Pterosaurs (Ramphorhyncus), sometimes with a
rudder-like expansion of the end of the tail, and short-tailed
Pterosaurs (Pterodactyl), with compact bodies and keeled breasts,
like the bird. In the earlier part of the period they all have
the heavy jaws and numerous teeth of the reptile, with four or
five well-developed fingers on the front limbs.
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