Continu et discontinu dans une évolution de foraminifères planctoniques du Crétacé supérieur

Abstract

Within the populations of the gradual lineage including Contusotruncana fornicata (Plummer) (Globotruncanidae), the spiral heights increase with time. The speed of this increase is linked to the asymmetries in the distributions of the index used to measure the spiral heights. The succession of these asymmetries shows an evolutionary process, combining gradualist continuity and discontinuities by successive evolutional jumps. These two coexisting modes could be induced by genetic mechanisms evoked for phyletic gradualism and punctualism respectively.