The sketches of four skeletons above show similarities in the arm bones of different types of animals that span a range of more than 200 million years. Each time one of these animals evolved to fly, important parts of the wings were attached to the bones of the hand (shown in green).
In each case, the hand has a different adaptation, including the very long “little” finger in the pterosaur and the fusion of many of the individual bones of the hand in present day birds. The outer half of the bat wing is suspended from four very long fingers.
The wrist is one of the most important joints in a bird’s body. It allows the primary (outer) wing feathers to move through the air to produce forward thrust on the downstroke of flapping flight. On the upstroke, movement of the wrist subtly alters the orientation of the wing. Without this movement, the forces from upstroke and downstroke could cancel each other out.
LEARN MORE about Wing Bones
KIDS QUESTION: In the museum exhibit we asked: What is the largest animal that has ever flown?
The answer is: A Pterosaur
Fossilized remains of the pterosaur Quetzalcoatlus, discovered in Texas in 1971, is the largest animal currently known to have flown. It was estimated to have a wingspan of 35 feet (10.7 meters).