Palaeoecological methods for assessing marine ecosystem recovery following the Late Permian mass extinction event

Different authors use different methods to assess Permian–Triassic palaeoecological changes, yet no comparative study of different methodologies has been published. We compared two methods of assessing palaeoecological parameters such as diversity, richness and skeletal abundance from limestone thin sections: point-counting and an equal area approach. Results demonstrated that there are significant differences between methodologies. Point-counting is relatively quick but has drawbacks. It is biased with respect to organism size, over-estimates larger taxa/bioclasts, and underestimates smaller taxa/bioclasts. Some point-counting palaeoecological data are not considered useful for measuring biotic recovery because they are affected by taphonomic processes: for example, the presence of diagenetic veins may reduce presumed skeletal abundance; winnowing may increase it. Trends in abundance between locations and regions through time, however, tend to broadly agree between methods, although we recorded Early Triassic samples with much higher skeletal abundances (up to 75%) than in previous published studies. Data from locations in Italy, Oman, and USA were compared. The most diverse samples are Early Induan (Griesbachian) in age from Oman, whilst the Late Induan–Early Olenekian (Dienerian–Smithian) samples from western USA are less diverse. These data agree with previously published inferences of regional variability in recovery rates from field-based macrofossil analyses of tiering and trace fossils.