Scarabaeoidea sensu Crowson 1981

Assigning feeding or other ecological traits to fossil beetles is notoriously difficult. Narrative scenarios have some appeal and may be intrinsically consistent (e.g., Ponomarenko 2003), but rely on extensive interpretations of sparse evidence. We have only two sources of evidence: fossilized traces of feeding activities and optimizing feeding habits of extant taxa onto cladograms (e.g., Scholtz and Chown 1995). Fossilized evidence of feeding activity of insects refers mainly to phytophagy and coprophagy. Traces of leaf feeding are frequently documented in the fossil record (Scott et al. 1992), but identifying the tracemakers is virtually impossible. The fossil evidence for coprophagy is large, and assigning it to the Scarabaeoidea is straightforward if we consider scarabs to be the only dung feeders producing dung balls and tunnels.

Beutel and Leschen (2005) identified saprophagy as an apomorphy for all Polyphaga taxa included in their analysis. It was hypothesized to be the ancestral feeding habit of the hydrophiloid lineage (Hydrophiloidea, Histeroidea, and Scarabaeoidea) by Hansen (1997 b) and of 'laparostict' scarabs by Cambefort (1991). However, by mapping extant feeding habits onto the then latest phylogenetic tree, Scholtz and Chown (1995) identified mycetophagy as plesiomorphic conditions for the adults and humus feeding for the larvae of scarabaeoids. The topology of the scarabaeoid tree has changed since, and some extant feeding habits were not considered in the analysis, e.g., coprophagy in adult Trogidae (Krell et al. 2003 and references therein), predatory Hybosoridae and Cetoniinae, sap-feeding Dynastinae and Lucanidae, and necrophagy in Cetoniinae. A new analysis is beyond this review but necessary to test the hypothesis of a fungus-feeding scarabaeoid stem species with humus-feeding larvae.