Bone age is used widely by pediatricians to assess the skeletal maturity of a child and predict growth potential. This entails measuring the size of secondary ossification centers (SOCs), which develop with age in the ends of long bones, which are initially cartilaginous. However, little is presently known about the developmental biology, evolution and functional role of these skeletal elements. Here, we summarize the knowledge currently available in this area and discuss potential primary functions of the SOC.