Figure 7. Evolutionary transformations of a polycystine lineage through time. The fact that radiolarian shells preserve in the sediments for millions of years makes them especially useful for the investigation of evolutionary changes. These figures show selected representatives from a continuum of morphological change that took place in the subgenus Podocyrtis (Lampterium) from 47 to 41 million years ago. After the last form illustrated, the lineage became extinct, leaving no descendants. Assembled by W. R. Riedel, using illustrations published in Micropaleontology, vol.24, p.89, courtesy of Micropaleontology Press.