Incompleteness of the Permian–Triassic fossil record: a consequence of productivity decline?

Analysis of published data shows that, for most animal groups, the fossil record in the immediate aftermath of the end‐Permian biotic crisis is less complete than during the Late Permian or Middle Triassic. Completeness is measured by the Simple Completeness Metric. The interval of poor quality fossil record spans the entire Lower Triassic and may have serious consequences for our perception of the magnitude of the end‐Permian event. A model is presented which seeks to explain this phenomenon. There is abundant evidence that levels of primary productivity were severely reduced in the very latest Permian. In response to this, animal biomass must also have been reduced. The biomass of a particular taxon is the product of the size of individual organisms multiplied by the number of individuals. Those taxa that reduced population size, but maintained original body size, would tend not to be preserved (apparent extinction) and would also be more prone to ‘real’ extinction. Those taxa that retained large population sizes, but reduced body size, would resist extinction and would also maintain their presence in the fossil record. One testable prediction is that taxa present in the fossil record in the immediate aftermath of the end‐Permian crisis will have smaller body size than their pre‐event relatives, regardless of their initial size. Anecdotal evidence supports this prediction. Such a biomass reduction model may also be applicable to other mass extinction events. Copyright © 2001 John Wiley & Sons, Ltd.