Figure 1.

Evolutionary modes of different characters in a hypothetical fossil fish lineage exemplify results from hundreds of published studies (Hopkins and Lidgard 2012, Hunt et al. 2015). (a) Population samples are taken at successive intervals from sedimentary layers that contain fossils. (b) Characters are measured for each sample. Different evolutionary modes are seen in character trajectories plotted against stratigraphic positions for eye width (c), tail fin length (d), and pectoral fin length (e). Illustration: Monica Jurik.