Figure 1.

Heterochronies that may result in paedomorphosis in salamanders. Lines (A–D) represent hypothetical developmental trajectories. The ancestral pattern is represented by metamorphic adults (A). Derived patterns resulting in paedomorphic adults include (B) hypomorphosis, where somatic development ceases before the metamorphic threshold (dashed horizontal line); (C) deceleration, where somatic development proceeds at a slower rate than A with the maturation threshold (dashed vertical line) being reached before the metamorphic threshold; (D) postdisplacement, where somatic development is initiated at a later ontogenetic age than A; or some combination of B–D (e.g., see ref. 4). Images modified from refs. 4 and 47.