Community replacement, ecological shift and early warning signals prior to the end-Permian mass extinction: A case study from a nearshore clastic-shelf section in South China

摘要

AbstractA quantitative investigation of the ecological changes of shallow-marine benthos was undertaken at the Permian–Triassic boundary section at Zhongzhai, South China. The studied fossil material primarily included brachiopods and bivalves owing to their abundance throughout the section, but other subordinate taxonomic groups including ostracods and microgastropods were also integrated for discussion.Overall, a succession of three benthonic paleocommunities was recognized representing three connected ecological evolutionary stages across the Permian–Triassic transition. Both Stage 1 and Stage 2 paleocommunities predated the end-Permian boundary mass extinction, and were characterized by relatively high diversity of brachiopods and bivalves, with no or very rare other taxa. Approaching the end-Permian mass extinction and the PTB itself, the paleocommunity abruptly changed and was replaced by the Stage 2 paleocommunity that was characterized by a relatively low Shannon's diversity (H) coupled with a high Simpson's dominance index (D) and, most notably, a changeover fromNeochonetestoTethyochonetes(both are brachiopod genera) as the most significant ecological dominants. This Simpson's dominance index (D) shift correlates well with food shortage (i.e. much reduced terrestrial influx and acritarch abundance), and is therefore interpreted to signify, possibly, intensified interspecific competitions withTethyochonetesseemingly outcompetingNeochonetespresumably due to its preadapted smaller body size. The post-extinction (Stage 3) pa