Heterochrony describes the evolutionary effects ofchanges in rate or timing of ontogenetic processes of adescendant compared to the ancestor, affecting its shape and size (Gould 1977; Alberch et al.1979 ; McNamara1997).As we concentrate here on the change of size, notso much on change of shape, we follow the more generalterminology of McNamara (1997) and Long andMcNamara (1997).‘‘Accel eration’’ thus also refers toan increase in the rate of overall body growth and notonly to an increase in the rate of shape change of aparticular structure, the latter being the original definitionof Alberch et al.(1979) .