Figure 2.4 The evolutionary history of cephalopods is here mapped onto the earth’s geologic timescale. Species of squid, cuttlefish, and all the rest that we see in the ocean today are merely the latest descendants of their storied lineages—they themselves were not around in the Triassic! Internal anatomy is drawn in coleoids to illustrate the steps of shell reduction, and it is omitted in externally shelled cephalopods to show shell ornament. Dotted lines indicate genera whose stories are told in the text; all other lines represent substantial taxonomic groupings. Danna Staaf and C. A. Clark
