WHAT DOES THE “LILLIPUT EFFECT” MEAN?

The miniaturization of faunas during the recovery from mass extinctions – the “Lilliput Effect” – is a feature that has been documented in various groups following mass extinction events. Fundamental questions still exist regarding how ubiquitous the phenomenon may be temporally, spatially, and taxonomically, but, potentially more importantly from evolutionary perspectives, we also require a better understanding of what mechanism(s) is/are operating to produce the effect. From a theoretical perspective, there are several possibilities to explain the trend, including: 1) small taxa preferentially survive mass extinction events; 2) newly evolved clades that appear during radiations will be small as prescribed by Cope's Rule; and 3) the evolutionary response within established lineages was to reduce the average size of species in ‘violation' of Cope's Rule. In order to test these various possibilities there are a range of data that need to be generated. Important data would include: 1) well-constrained phylogenies that can be used to place the morphologic data into context; 2) detailed morphologic data on relatively large populations to document the size changes; and 3) sclerochronologic analyses of specimens so that changes in the rates of ontogenetic develop can be investigated to determine if changing growth strategies, hence elements of heterochrony, played a role in the size changes. With these data in hand, we can more effectively examine not only the dynamics for individual mass extinction, but also to test whether mass extinctions forced by different causal mechanisms produced different types of biotic responses even if in both cases the “Lilliput Effect” was operating. Furthermore, it would be important to document if these species fill the role of disaster or opportunistic species which undergo dramatic increases in abundance during intervals of environmental disruption with little evolutionary potential or if they represent the progenitors from which dominant, post-extinction clades evolve.