Traceback ages (see text) of YSOs for NGC 2264 N (left column), NGC 2264 S (middle column), and Collinder 95 (right column). Each row represents a different subpopulation. First row : all identified YSOs in each cluster. Second row : YSOs with |Δθ| ≤ 50°. Third row : YSOs with |Δθ| ≤ 50° with the additional requirement of a current distance from the cluster center greater than the half-mass radius and a distance of closest approach to the cluster center of less than the half-mass radius. The median and ±1σ range of the distributions are indicated.