Terrestrial tetrapods and the end Permian event: A comparison of analyses

Previous analyses of changes in diversity of Permo‐Triassic tetrapods are reviewed and compared. Biases inherent in such studies which distort the picture of diversity change are discussed. A new analysis of change in generic diversity of the tetrapods of the Karoo Basin, South Africa is presented. Various factors which could bias the results, namely, inconsistent taxonomy, insensitive stratigraphy, area of exposure per time interval, and differing intensity of collecting are addressed and corrections made for them. The results of the new analysis are compared to those of previous ones. In particular it is noted that, contrary to the results of other studies, large decreases in generic number are recorded not once, but twice in the Late Permian sediments, the second occurring in sediments dating from well before the close of that Period. It is concluded that stratigraphic sensitivity is the most important biasing factor in the present analysis and the implications of this for other diversity studies, and for explanations of diversity change, are emphasized.