(A) Changes in the proportion of time spent in specific vocal, postural, and locomotor behaviors across development. Behaviors that increase or decrease are denoted with asterisks to represent significance values. (B) Developmental trajectories of contact call maturation (i.e., mature phee calls relative to immature cries), postural maturation (i.e., hindlimb support relative to righting reflex), and locomotor maturation (i.e., walking relative to crawling). Points represent session values, gray curves represent the cubic spline fits for individual marmosets, and black curves represent the population cubic spline fits. (C) Illustration of hypothesized sequences between contact call and postural/locomotor developmental trajectories and (D) an overview of the observed developmental trajectories. (E) Comparison of the different developmental time courses. Bars and whiskers represent mean ±2 SE. Significance values are represented by ‘*' (p<0.05), ‘**' (p<0.01), ‘***' (p<0.001) and ‘****' (p<0.0001).