Rolling into a ball: phylogeny of the Ceratocanthinae (Coleoptera: Hybosoridae) inferred from adult morphology and origin of a unique body enrollment coaptation in terrestrial arthropods

Abstract

Results of a phylogenetic analysis of all but one of the 43 recognized extant genera of Ceratocanthinae scarab beetles (Coleoptera: Hybosoridae) are reported. The analysis is based on 97 parsimony informative adult morphological characters scored for 61 ingroup and 10 outgroup terminals. This pantropical subfamily of some 366 species is remarkable for the adults’ ability to pack their body into a tight sub-sphere using interlocking exoskeletal structures (= enrollment coaptations). An overview on known biological and fossil data on the subfamily is provided, as well as a list, an overview, a key and illustrations of adults of all Ceratocanthinae genera. The phylogenetic analysis supports a monophyletic Ceratocanthinae (bootstrap 76%) and a basal dichotomy between pantropical Ceratocanthini (97%) and the South American clade (98%) of Scarabatermitini. Ivieolini renders Scarabatermitini paraphyletic. Another well supported internal clade is the Philharmostes group of seven Afrotropical genera (85%). All other inclusive clades detected in the analysis have low bootstrap support (51–65%), likely indicative of limitations of the adult morphological dataset. We also provide a detailed distribution map of Ceratocanthinae and hypothesize about the South American origin of the subfamily, and that of its two subclades: Ceratocanthini and Scarabatermitini + Ivieolini. Overall this paper summarizes all existing information on Ceratocanthinae beetles in an evolutionary context in order to facilitate and stimulate further research on this subfamily.