Recovery of Biodiversity after the Late Permian Extinction Event: Definitions and Approaches

Understanding post-extinction recovery of marine ecosystems is hindered by a lack of rigorous, widely applicable method(s) of quantifying biotic recovery. Concepts need to be defined and methods of quantifying recovery need to be devised, tested and revised where necessary. After modern, small scale disturbances to the marine ecosystem recovery is measured by ecological succession and can simply be defined as the interval of time between the event occurring, and the return to pre-event conditions(with the caveat that biological systems rarely, if ever, return to a precise pre-event state). In the geological past, major extinction events resulted in the permanent loss of some taxa and/or ecological restructuring on such a scale that a return to pre-event conditions was not typically possible. If we accept that there is a difference between ‘background' and ‘extinction' times then the return to background conditions should be recognizable. The question is how? The simplest methods rely on measures related to taxonomic richness. An alternative is to use paleoecological methods. As the taxonomic and ecological effects of extinction events are to some extent decoupled these methods should be viewed as complimentary. The best methodology should enable comparisons of rates of recovery (1) between regions, individual localities and/or environmental settings, (2) between geological events of different scales, and (3) between ancient and modern events. Using the Permian-Triassic as an example, we compare several published methods of quantifying biotic recovery. Sites in Italy, USA, Oman, Svalbard and Japan were studied, and the results compared. Preliminary results have indicated that after the Late Permian event, the shallow marine settings of Neotethys were sites of the most rapid initial recovery and that outside Neotethys, higher paleolatitudes recovered quicker than lower paleolatitudes. Published methodologies based on point-counting are rejected as being significantly influenced by taphonomic and diagenetic factors.