Adaptive radiation
Nevertheless, when several distinctly new lines appear within a short period, it seems reasonable to say that the rate of change has been surprisingly fast. An example would be the appearance of new reptilian groups in the Upper Triassic. Using the term 'reptile' broadly, the groups include dinosaurs, pterosaurs, Chelonia (turtles), crocodylomorphs (early Crocodilia), phytosaurs, and ichthyosaurs a bit earlier (Middle Triassic).