The origin and evolutionary history of necrophagy in Scarabaeinae (Coleoptera, Scarabaeidae): a comprehensive analysis of South American Coprinisphaera

Abstract

The ichnospecies Coprinisphaera tonnii and Coprinisphaera akatanka, both attributed to necrophagous Scarabaeinae, were analysed in the context of palaeoenvironmental and palaeoclimatic conditions during the South American Cenozoic to shed light on the origin and evolutionary history of necrophagy in Scarabaeinae. The material examined comprised 5340 Coprinisphaera from nine formations in Argentina, Chile, Uruguay and Ecuador, ranging in age from the early Eocene to the Late Pleistocene representing several South American Land Mammal and Palaeosol Ichnofossil Ages. New records of Coprinisphaera from the Sarmiento, La Pava, Río Frías and Tafí del Valle formations are described for the first time. The ichnological evidence presented herein refutes the widely accepted hypothesis that the Late Pleistocene South American megafaunal extinction triggered necrophagy in Scarabaeinae. The new hypothesis proposes that necrophagy in Scarabeinae arose in Patagonia during the middle–late Eocene in response to intense competition among coprophagous Scarabaeinae for herbivorous dung. Necrophagous dung beetles would have cohabited with the coprophagous ones in temperate–warm grass-dominated environments inhabited by herbivorous mammals, using the herbivorous corpses as provisions. Necrophagy seems to have been a successful feeding strategy, as reflected by a first burst of necrophagous Scarabaeinae during the Middle Miocene. By the Late Miocene, a shift towards more arid and colder conditions in Patagonia probably imposed palaeoenvironmental stress on necrophagous dung beetles. By the Pleistocene, a second burst of necrophagous Scarabaeinae occurred in central and northern Argentina. By then, necrophagous Scarabaeinae would have started to consume small vertebrate corpses and inhabit cold semiarid habitats with scarce grasses.