Gradual evolution of the Early Cretaceous marine gastropod Rissoina lineage in Central Poland

The evolutionary changes of the Early Cretaceous (Valanginian) marine gastropod Rissoina (Buvignieria) sp. from Wąwał (central Poland) show a pattern typical of the Ancient Lake Concept. Its morphology is stable during period of unstable conditions and starts to change gradually when the environment becomes stable. The linear character of the evolutionary changes of Rissoina sp. and lack of evolution among co−occuring gastropods suggests that the rate of evolution was controlled by intrinsic factors, not the environment.