Lower extinction rates of clams than of brachiopods, and their eventual replacement of brachiopods by clams during the Phanerozoic. Note the importance of the Permian- Triassic Extinction event. The diversity of brachiopods never recovered, but clams became increasingly speciose.

(after) Gould, S.J. and Calloway, C.B. 1980. Clams and brachiopods: ships that pass in the night. Paleobiology 6: 383-396.