The evolution of gigantism in sauropod dinosaursfrom prosauropods, and of the body plan changeslinked to this, are an obvious case of a pattern ofheterochrony termed peramorphosis (Long and McNamara1997) in which the descendant has a larger bodysize than the ancestor, and the juvenile descendantresembles the adult ancestor whereas the adult descendantis more ‘developed’.However, which process ofheterochrony produced the gigantic body size ofsauropod dinosaurs had not been understood untilrecently.Becau se a number of recent studies (Rimblot-Baly et al.1995 ; Curry 1999; Erickson et al.2001 ;Sander 2000) detected very fast growth in several taxa ofMiddle and Late Jurassic sauropods based on examinationsof their bone histology, it was suggested that anincrease in growth rate (acceleration) compared toprimitive dinosaurs was responsible (McNamara 1997).At the time, however, the very large Late Triassicsauropod was not known yet, and a model of prolongedacceleration from the Late Triassic to the Late Jurassic,i.e. a gradual phyletic size increase, seemed tenable toaccount for sauropod gigantism.