English: Graph showing the number of trilobite families from the start of the Middle Devonian to the total extinction at the close of the Upper Permian. Numbers behind the periodes give these numbers. Heights correspond to duration of the Epochs/Ages. Colors code for trilobite orders: Proetida - brown, Phacopida - steelblue, Lichida - clearblue, Harpetida, Odontopleurida and Corynexochida - pink, olive and purple. Based on: Feist, R. (1991). The Late Devonian Trilobite crisis. Historical Biology5: 197-214, and Feist, R. (2002). Trilobites from the latest Frasnian Kellwasser Crisis in North Africa (Mrirt, central Moroccan Meseta). Acta Palaeontologica Polonica 47 (2): 203–210