= Tetrapod limb
A <tetrapod limb> is a paired appendage of a <tetrapod>, such as a <forelimb> or <hindlimb>, organized around a shared inherited skeletal pattern. In a familiar <forelimb>, one proximal <bone>, the <humerus>, is followed by the <radius bone> and <ulna>, then more distal elements and <limb digits>. The corresponding structures can differ greatly in proportions and use. Comparing their relationships, rather than just their overall shape, is central to recognizing <homology (biology)>.
The transition from a fin to a limb was not an instantaneous appearance of an entire new skeleton. A 2006 study of <Tiktaalik> described a pectoral fin with an expanded distal internal skeleton and articulations permitting a substrate-supported posture. The reconstructed <joint (anatomy)> configurations included flexed shoulder and elbow regions and an extended distal region. This indicates precursors of limb-like support in a finned animal; it does not make every distal fin element a <limb digit>.<The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb by Neil H. Shubin and others>[Abstract; Figures2,6–7, skeleton, joint surfaces and reconstructed postures]{ref}
A useful comparison traces the <humerus>, <radius bone> and <ulna> in two differently shaped <forelimbs>, then asks which elements contact one another. A wing and a walking appendage can preserve corresponding elements while redistributing their lengths and mechanical roles. Shared ancestry and present function are related questions, but one cannot be read directly from the other.
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