Biogeographical and co-evolutionary origins of scarabaeine dung beetles : Mesozoic vicariance versus Cenozoic dispersal and dinosaur versus mammal dung

Abstract

The subfamily Scarabaeinae (Coleoptera: Scarabaeidae) may have originated in Gondwanaland, through Mesozoic vicariance or dispersal in association with dinosaur dung, or through Cenozoic dispersal in association with mammal dung. We review evidence from age-calibrated phylogenies, fossil records, biogeographical patterns, and ecological associations. Fossil calibrated phylogenies for Scarabaeoidea predict a Cretaceous origin for Scarabaeinae, although age estimates would rely on other scarabaeoid groups given the doubtful validity of Mesozoic ‘scarabaeine’ fossils. Molecular clock calibrated phylogenies for Scarabaeinae predict an early Cenozoic origin coeval with modern mammal diversification. Trace fossil evidence suggests the exploitation of dinosaur dung by fossorial insects, although scarabaeine fossils are only validated for the Cenozoic. Although we discuss fossil evidence for dinosaur dung as a faunal resource, the origin of modern scarabaeines from an earlier Mesozoic vicariant or dispersal fauna remains unsupported. Although clock-constrained, phylogram topography is consistent with early Cenozoic palaeoclimatic and palaeoecological events, Eocene marine barriers would demand dispersal to explain the distributional origins of Scarabaeinae. Inconsistencies between classification and phylogeny complicate biogeographical analysis, although earlier southern radiation of basally-derived tribes has probably been followed by later diversification and the global dispersal of both basally and terminally-derived taxa, primarily via restored land links.