Birds are considered dinosaurs. Specifically, they belong to a group of dinosaurs called the maniraptors. Maniraptors in ancient times included many two-legged, toothy predators, such as the Velociraptor and its relatives. These creatures shared so many features with early birds that they are now considered part of the same group.
All maniraptors, including birds, have a special bone in their wrists called the semilunate carpal. This bone allows them to fold up their arms so that the pinky side of their paw or wing points up and backward toward the elbow. In birds, this allows for powered flight, but it may have originally evolved for grasping prey tightly or to protect delicate arm feathers. Many ancient maniraptors were feathered, though it is unknown how many could fly. Maniraptors share other features seen both in ancient predators and modern birds, including a fused clavicle or wishbone, a keeled sternum or breastbone, long arms, and hollow bones.