Which organs in two animals indicate that they are derived from a common ancestor?

When different animals which have organs originated from the same part of the body but function differently then they are known as homologous organs.

Example: wings of a bat, wings of birds, dolphin, flipper and human arm are the homologous organs. They all are derived from the same set of bones which are humerus, radius, ulna, carpals, metacarpals, and phalanges. But all of them function differently.