Morphometric analysis of fossil bumble bees (Hymenoptera, Apidae, Bombini) reveals their taxonomic affinities

Abstract

Bumble bees (Bombusspp.) are a widespread corbiculate lineage (Apinae: Corbiculata: Bombini), mostly found among temperate and alpine ecosystems. Approximately 260 species have been recognized and grouped recently into a simplified system of 15 subgenera. Most of the species are nest-building and primitively eusocial. Species ofBombushave been more intensely studied than any other lineages of bees with the exception of the honey bees. However, most bumble bee fossils are poorly described and documented, making their placement relative to otherBombusuncertain. A large portion of the known and presumed bumble bee fossils were re-examined in an attempt to better understand their affinities with extant Bombini. The taxonomic affinities of fossil specimens were re-assessed based on morphological features and previous descriptions, and for 13 specimens based on geometric morphometrics of forewing shape. None of the specimens coming from Eocene and Oligocene deposits were assigned within the contemporary shape space of any subgenus ofBombus. It is shown thatCalyptapis florissantensisCockerell, 1906 (Eocene-Oligocene boundary, Florissant shale, Colorado, USA) andOligobombus cuspidatusAntropov, 2014 (Late Eocene, Bembridge Marls) likely belong to stem-group Bombini.Bombus anacolusZhang, 1994,B. dilectusZhang, 1994,B. luianusZhang, 1990 (Middle Miocene, Shanwang Formation), as well asB. vetustusRasnitsyn & Michener, 1991 (Miocene, Botchi Formation) are considered as species inquirenda. In the Miocene, affinities of fossils with derived subgenera ofBombuss. l. increased, and some are included in the shape space of contemporary subgenera:Cullumanobombus(i.e.,B. pristinusUnger, 1867,B. randeckensisWappler & Engel, 2012, andB. trophoniusProkop, Dehon, Michez & Engel, 2017),Melanobombus(i.e.,B. cerdanyensisDehon, De Meulemeester & Engel, 2014), andMendacibombus(i.e.,B. beskonakensis(Nel & Petrulevičius, 2003), new combination), agreeing with previous estimates of diversification.