PATTERNS AND PROCESSES OF HETEROCHRONY IN MESOZOIC GONIASTERID SEA-STARS

Heterochronic processes are obvious in the most common family of Mesoz oic asteroids, the Goniasteridae, whether studied from entire fossils or, as is more frequently the case, from isolated ossicles. When phylo geny is poorly known, comparison between species leads to such unsatis factory interpretations as 'A is more paedomorphic than B' or 'C, comp ared with other species, has many peramorphic characters'. When the ph ylogeny is known, heterochronic trends appear amongst the lineages. Th e peramorphocline Metopaster parkinsoni - M. loirensis - M. trichilae - M. chilipora- M. hypertelicus is studied here from the Cenomanian to the Upper Campanian of France. Different morphological characters evo lved at different speeds. Among each polymorphous population, some mor photypes foreshadowed the next step. Juveniles of one species look lik e the adults of one of the ascendants. The dine developed irrespective of the substrate, and proceeded together with a migration from the An glo-Paris Basin to the Aquitanian Basin. Metopaster hunteri, during th e Coniacian, and Metopaster meudonensis, during the Upper Campanian, b oth evolved from Metopaster parkinsoni by neoteny, and provide a good example of reiterated and canalized morphological evolution. Some non- heterochronic canalizations are described.