The implications of the giant bivalve family Alatoconchidae for the end‐Guadalupian (Middle Permian) extinction event

Abstract

The end-Guadalupian extinction is an important biotic event in the Phanerozoic with an ecological impact comparable to the 'big five' extinctions. However, the age, pattern, and mechanism of this extinction are all under debate. The bivalves of the Alatoconchidae family attained body volumes up to 10,000 cm 3 and had a wide distribution in the low latitude Palaeotethys and Panthalassa. These giant clams originated in the early Kungurian and went extinct in the Late Guadalupian. Therefore, they are the typical victims of the end-Guadalupian extinction and are major index fossils for the understanding of this event. Although extraction of these giant bivalves from the host-resistant limestone is hard, plenty of new-found transverse sections on outcrops are available for morphological reconstruction and volume estimation. The measurement from the representative fossil localities in South China indicates the clams achieved a substantial volume increase during the Wordian and sustained the giant size to the late Capitanian, till their abrupt disappearance. The giant clams originated under atmospheric hyperoxia and warm climate after the Late Palaeozoic Ice Age. Their body volume increase was roughly parallel to the seawater warming. The accompanied high seawater carbonate saturation and Mg/Ca ratio are beneficial to their biomineralization of the large shells with aragonite or high-Mg calcite components. On the contrary, these giant bivalves were probably killed by the major or rapid changes of those environmental factors that once facilitated their success, such as drastic fluctuation of seawater temperature, sudden ocean acidification, and marine anoxia.