Low functional evenness in a post-extinction Anisian (Middle Triassic) paleocommunity: A case study of the Leidapo Member (Qingyan Formation), south China

Functional diversity, defined as the abundance and distribution of traits present in a community, has important implications for the functioning of ecosystems in the wake of events of major disturbance. Here, we examine the functional diversity of a Middle Triassic paleocommunity in the wake of the largest mass extinction in Earth's history, the Permo-Triassic mass extinction (PTME). Field data was collected and analyzed for a highly diverse invertebrate marine fossil assemblage, the Middle Triassic (Anisian) Leidapo Member (Qingyan Formation) of Qingyan, south China. Previously interpreted to represent a fully restructured paleocommunity in the aftermath of the PTME, our results indicate that the fauna of Leidapo Member had high taxonomic diversity and high functional richness, however was functionally uneven. Despite the presence of 24 different functional groups, the paleocommunity was numerically and ecologically dominated by one functional group consisting of mostly attached epifaunal suspension feeding brachiopods. The overwhelming dominance of this Anisian paleocommunity by one functional group implies that either, 1) resource availability in the community was uneven, and/or 2) strong environmental or niche filtering was in effect. As such, while the Anisian Leidapo Member paleocommunity was deposited in a fairly stable shallow water paleoenvironment, this biotic assemblage would have been very vulnerable to biotic and environmental perturbations. While it is uncertain whether or not this pattern is typical of paleocommunities in the aftermath of the PTME, these results imply that some Anisian paleocommunities may not have been as fully restructured as previously thought, and may have been inherently unstable due to the numerous biotic and environmental changes present in the Triassic.