James River Bridge

These wonderful three eyases are 12 days old and growing fast. Very well visible it the development of the anatomy of the wing. At the first days the wings where more like arms with very large hands. But now one can see very well how the pagatium is growing. This is the piece of skin between the shoulder and the wrist. It is a very important part of the wing. The front edge of the pagatium is formed by the patagial tendon which is very susceptible to injury. For instance when a bird flies into a wire this tendon is likely to be severely damaged. Tendons do not heal easily, and that means that the bird may never be able to fly again.

The pagatium is an evolutionary asset, and a major part of the arm to wing eveolution. Wings evolved over many, many millions of years. Scientists have extensively studied the wings of modern-day birds and have identified many important anatomical details. Especially important are those not found on the "arms" of non-birds. Major efforts have gone into finding early occurrences of such details in the fossil record, but unfortunately it is far from complete. Wings generally have thin, hollow bones that do not fossilize well and it appears that few of the animals that had them died in environments suitable for fossilization. The lack of fossils makes it difficult to establish the time that each feature first appeared. The times listed below are documented, but do not reflect an even progression from one step of deveopment to the next.