Mastigocoleidae fam. nov., a New Mesozoic Beetle Family and the Early Evolution of Dryopoidea (Coleoptera)

With some 3,700 described species, Dryopoidea are a moderately diverse superfamily of beetles whose position within basal Polyphaga has been historically difficult to elucidate. Members of most extant dryopoid families are set apart from the majority of other polyphagans by their association with aquatic habitats, but little is known about the origin of these derived life habits and the phylogeny of the superfamily. Here we describe Mastigocoleidae Tihelka, Jäch, Kundrata & Cai fam. nov., a new family of Mesozoic dryopoids represented by fossils from the Cretaceous Yixian Formation in northeastern China (undescribed species; ~125 Ma), Crato Formation in northeastern Brazil (Mastigocoleus rhinoceros Tihelka & Cai gen. et sp. nov.; ~113 Ma), and amber from northern Myanmar (Mastigocoleus resinicola Tihelka & Cai gen. et sp. nov. and Cretaceocoleus saetosus Tihelka, Kundrata & Cai gen. et sp. nov.; ~99 Ma). Integrating the findings of recent molecular and morphological phylogenetic analyses, we recover Mastigocoleidae as an early-diverging dryopoid clade sister to the families Lutrochidae and Dryopidae, or less likely as a group of putative stem-dryopoids. Mastigocoleidae are most distinctly separated from all other dryopoid families by their whip-like antennae, with 11 antennomeres, reaching to the pronotal base, and with the scape broadest and longest, a short pedicel, and antennomeres II–XI more or less distinctively gradually tapering toward the apex. Mastigocoleidae indicate that the last common ancestor of Dryopoidea was likely terrestrial in the adult stage, and document character acquisitions associated with a specialization for aquatic life.