Temporal shell-size variations of bivalves in South China from the Late Permian to the early Middle Triassic

Abstract

During the end-Permian mass extinction and subsequent Early-Middle Triassic recovery, a series of environmental changes occurred and were accompanied by morphological and ecological responses. This study presents a shell-size analysis study of Upper Permian through lower Middle Triassic bivalve fossils from South China to discover their ecological and environmental implications. With a dataset of over 4900 bivalve specimens from published monographs and our own collections, shell length and shell height are measured and analyzed with a substage-stage binned scale. The mean and median sizes of bivalve shells show a significant Lilliput effect in the immediate aftermath of the end-Permian mass extinction. However, both epifaunal and infaunal bivalves grew larger quickly during the late Griesbachian, indicating a quick rebound of bivalve shell size. The temporal variations in bivalves in South China were mainly controlled by biotic and abiotic factors, e.g., physiological adaptation, changing competition, predatory pressure, and climatic and oxygen changes.