Events during Early Triassic recovery from the end-Permian extinction

Abstract

The Palaeozoic–Mesozoic transition is characterized not only by the biggest Phanerozoic mass extinction, at the end of Permian, but also a prolonged period of recovery of the biota during the succeeding Early Triassic. The delayed recovery is generally attributed to the effects of extreme environmental conditions on the Early Triassic ecosystem. However, there has been very little study of the cause and mechanism of the environmental conditions that prevailed during the period of extinction and subsequent recovery. Research on the Permian–Triassic boundary and Lower Triassic, especially that on environmental events at the beginning of the Triassic in South China, indicates that the slowness of the recovery may be the result of three factors: (1) extreme environmental conditions that persisted through the transitional period and which were maintained by, for example, intermittent contemporary volcanism; (2) a passive evolutionary and ecologic strategy of the biota, in which r-selection taxa were dominant and K-selection forms insignificant; (3) an immature, poorly functioning ecosystem, which had difficulty in responding to and withstanding extreme environmental changes. According to data from South China, environmental changes were frequent during the Late Permian, and especially serious at the Permian–Triassic boundary. The Late Permian ecosystem was well structured and fully functioning as a result of a long period of steady development during the late Palaeozoic, and was capable of resisting general environmental changes. However, increasingly frequent and probably more extreme environmental events in the latest Permian may have led to a general collapse of this ecosystem and to the mass extinction at the end of the Permian. The Early Triassic ecosystem was immature, functioned poorly, and was unable to respond effectively to environmental changes, so that persisting extreme environmental conditions slowed ecosystem reconstruction considerably, and the recovery of the biota therefore took a relatively long time. The environmental events at the Permian–Triassic boundary might not be significantly different from those at other Phanerozoic transitions, but they consisted of a series of events that occurred at intervals during the transitional period.