Skeleton
Hierarchical bone structure for animation
Also known as: Bone hierarchy · Armature · Rig
Definition
A skeleton is the hierarchical tree of bones that drives mesh deformation through skinning. Each bone has a parent (so moving the shoulder moves the elbow that moves the wrist), a local transform, and a list of vertices it influences. AAA character skeletons typically have 80-200 bones — main body, fingers, jaw, eyes, plus utility bones for tweak controls and twist correction.
In production
Use a clean naming convention: `bn_spine_01`, `bn_arm_l`, `bn_finger_index_03` etc. Animation retargeting tools (UE5, Mixamo, MotionBuilder) rely on matching bone names across rigs to transfer motion, and UE5's IK Retargeter additionally requires a defined root bone and consistent bone chain length to solve foot-sliding and pole-vector issues during retarget. Utility bones — twist bones on the forearm, for example — aren't part of the base FK chain but are driven by constraints to fix candy-wrapper deformation at the elbow and wrist during rotation. A common mistake is building a skeleton with inconsistent bone roll/orientation between the left and right sides, which breaks mirrored animation and forces animators to hand-fix poses per side. Maya's HumanIK and Blender's Rigify both ship standardized skeleton templates that studios often customize rather than build from scratch, since matching an industry-standard hierarchy makes it far easier to plug in motion-capture data without a full retarget pass.
