This paper presents a precise kinematic skeleton extraction method for 3D dynamic meshes. Contrary to previous methods, our method is based on the computation of motion boundaries instead of detecting object parts characterized by rigid transformations. Thanks to a learned boundary edge function, we are able to compute efficiently a set of motion boundaries which in fact correspond to all possible articulations of the 3D object. Moreover, the boundaries are detected even if the parts linked to an object's articulation are immobile over time. The different boundaries are then used to extract the kinematic skeleton. Experiments show that our algorithm produces more precise skeletons compared to previous methods. Experiments show that our algorithm produces more precise skeletons compared to previous methods.