Fig. 2 in The fossil record of early tetrapods: Worker effort and the end-Permian mass extinction

Fig. 2. Perceptions of early tetrapod diversity at three points in research time, 1900, 1950, and 2000. Total numbers of valid species are indicated per series; the 1900 data distribution differs significantly from those for 1950 and 2000, but the 1950 and 2000 distributions do not differ significantly (see text).