Evolutionary changes in the biometry of the fossil radiolarian Stichocorys peregrina lineage in the eastern equatorial and eastern North Pacific

► The S. peregrina lineage can be subdivided into two morphotypes geographically. ► The ET can be used as a primary biostratigraphic marker in the low latitudes. ► There is a correspondence between the evolutionary and paleoceanographic events. ► The morphologic changes should be assigned to a sympatric/parapatric transition.