Abstract

Disaster taxa are long-ranging opportunistic generalists that briefly proliferate in the aftermath of mass extinctions, invading vacant ecospace until forced to return to more marginal settings through competition with specialist taxa returning from refugia. Lowermost Triassic (Griesbachian) strata worldwide have been noted for a brief ‘proliferation of Lingula’, a classic ‘living fossil’, which through its long fossil record typically has occurred in shoreface and dysoxic settings. The abundance of Lingula relative to other taxa in the Griesbachian Dinwoody Formation of southwestern Montana and western Wyoming (USA) has been quantified and the results placed into a paleoenvironmental context. Lingula dominates the fossil assemblage in the Dinwoody Formation across several facies deposited on an oxygenated, storm-dominated, mixed carbonate/siliciclastic shelf. A study of preservational state and quality further indicates that these results are not due to taphonomic bias. Lingula, therefore, behaved as a disaster taxon during the biotic recovery from the end-Permian mass extinction, much like relatively common Early Triassic normal marine stromatolites, that have been interpreted as disaster forms. Thus, while the fundamental rules of geology and biology have not changed, during biotic recoveries from mass extinctions organisms may behave and interact with their environments very differently than do their modern or fossil equivalents in “normal” times.

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