A bonanza of Cretaceous fossils provides insights into the evolution of antennal protection in clown beetles (Coleoptera: Histeridae)

Abstract

Species in the beetle family Histeridae exhibit numerous defensive adaptations, from a generally compact and spheroid body shape to retractable tarsi, legs, heads, and antennae. Modes of antennal concealment are particularly variable, underscoring the importance of protecting these essential sensory structures. Understanding the evolution of these morphological features has been hindered by a weak understanding of the family’s basal phylogeny, and corresponding patterns of niche-use and morphological evolution. Cretaceous amber fossils have been proliferating, filling in important morphological gaps right around the time of the family’s explosive radiation. Here we describe 10 new species from Cretaceous Burmese ambers, six of them representing new genera: Palaeabraeus glabrus gen. nov. et sp. nov. (Abraeinae); Pseudacritus extinctus gen. nov. et sp. nov. (Abraeinae); Miculissima excavata gen. nov. et sp. nov. (unplaced to subfamily); Placatister cascus gen. nov. et sp. nov. (unplaced to subfamily); Cretomalus tibiodentatus gen. nov. et sp. nov. (Dendrophilinae: Paromalini); Prodigister tricostatus gen. nov. et sp. nov. (unplaced to subfamily); Anapleus punctulatus sp. nov. (Dendrophilinae: Anapleini); Pantostictus hirsutus sp. nov. (Abraeinae: Pantostictini); Phasmister kraliceki sp. nov. (Onthophilinae); and Phasmister planatus sp. nov. (Onthophilinae). A revised phylogenetic analysis that includes these taxa supports previous hints that inquilinous forms were prevalent and diverse during the Cretaceous. These results also support the contention that pressures in these environments to protect the critically important sensory apparatus, the antenna, were strong, driving multiple origins of two of the more protective configurations among extant taxa. Some of the new genera remain unplaced to subfamily, underscoring the gaps that still remain in the early fossil record for the family, and the continued need for more comprehensive analyses of combined data from extant taxa, along with additional extinct forms that we may assume will continue to be discovered.