Regional Paleoecology of Early and Middle Triassic Paleocommunities: Implications for Biotic Recovery after the End-Permian Mass Extinction

Ashley A. Dineen
UW-Milwaukee, Department of Geosciences Milwaukee, Wisconsin, USA
[email protected]

Published data has been interpreted as indicating that marine ecological devastation following the end-Permian mass extinction was protracted and may have lasted 5 million years into the Middle Triassic (Anisian). However, a review of previous literature shows that understanding of biotic recovery is typically based on only a few components of the ecosystem, such as on taxonomic diversity, a single genus/phylum, or shallow water facies. Typically, paleocommunities are considered fully recovered when dominance and diversity are regained and normal ecosystem functioning has resumed. However, in addition to the biodiversity crash at the end of the Permian, taxonomic and ecologic structure changed, with the extinction marking the faunal shift from brachiopod-rich Paleozoic Evolutionary Fauna (EF) to the mollusc-rich Modern EF. This suggests that the extreme reorganizational nature of the Triassic does not adhere to the standard definition of recovery, which is a return to previous conditions. Thus, we propose the term “restructuring” to describe this interval, as Early and Middle Triassic communities might not exhibit the typical characteristics of a “normal” Permian one. To more fully characterize Triassic ecologic restructuring, paleoecologists should take into account functional diversity and guild structure. Preliminary statistics and field observations from south China, northern Italy, and the western US have indicated that Middle Triassic communities are characterized by high species diversity and functional richness, but lack large body sizes, high evenness, and complex guild structures. This indicates that full ecologic recovery after the end-Permian mass extinction may have taken longer than previously recognized.

AAPG Search and Discovery Article #90183©2013 AAPG Foundation 2013 Grants-in-Aid Projects