Structural classification is determined by how the bones connect to each other , while functional classification is determined by the degree of movement between the articulating bones .
Structural classification is how the bones connect to each other ; function is the degree of movement between the articulating bones .
A 2005 study by Sankar Chatterjee suggested that the wings of Microraptor functioned like a split-level `` biplane '' , and that it likely employed a style of gliding , in which it would launch from a perch and swoop downward in a ` U ' shaped curve , then lift again to land on another tree , with the tail and hind wings helping to control its position and speed .