Bombus (Mendacibombus) beskonakensis (Nel & Petrulevicius , 2003) Nel & Petrulevicius, 2003

Dehon, Manuel, Engel, Michael S., Gerard, Maxence, Aytekin, A. Murat, Ghisbain, Guillaume, Williams, Paul H., Rasmont, Pierre & Michez, Denis, 2019, Morphometric analysis of fossil bumble bees (Hymenoptera, Apidae, Bombini) reveals their taxonomic affinities, ZooKeys 891, pp. 71-118 : 71

Bombus (Mendacibombus) beskonakensis (Nel & Petrulevicius, 2003) comb. nov.

Holotype.

Female worker. MNHN-LP-B.47780 (BK349, coll. Paichelier, in 1977), part and counterpart, deposited in the Laboratoire de Palaeontologie, Muséum national d’Histoire naturelle, Paris, France. Type specimen has been located and revised ( Figs 1E , 3E ).

Type strata and locality.

Oligocene-Miocene boundary, 22.5 Ma, volcano-sedimentary paleolake, BesKonak Basin, Anatolia, Turkey ( Paichelier et al. 1978).

Diagnosis.

Habitus and hind and forewing venation similar to those of extant Bombini , with pterostigma short but longer than prestigma, and metatibial spurs not visible as preserved (seemingly obscured by leg orientation). Short process of proximal posterior corner of metabasitarsus apparently preserved. See Nel and Petrulevičius (2003) for original diagnosis.

Description.

Wing membrane red-brown, setose throughout; forewing length 15.0 mm; maximum width 5.2 mm as preserved; pterostigma slightly longer than prestigma, with posterior margin aligned with vein Sc+R; marginal cell with apex closed by strong vein; three submarginal cells of approximately same size; basal vein long, oblique and slightly curved in its base, slightly basad cu-a; cu-a straight; 1m-cu strongly curved apically in its anterior half, reaching second submarginal cell near midpoint; 2m-cu curved apically, reaching M basad to 2rs-m; second abscissa of Rs slightly double-curved; 1rs-m almost straight; 2rs-m with posterior half curved apically; prosoma length 6.3 mm, covered with long and dark hair; mouthparts not preserved, except for galea which is elongate; antennae approximately 3.5 mm long, with nine or ten visible flagellomeres, scape and pedicel poorly preserved; mesosoma length 8.0 mm, height 5.0 mm; metafemur length 4.2 mm, width 1.4 mm, with long curved hair; metatibia length 4.5 mm, width 1.8 mm, with corbicula; metabasitibial plate absent; metatibial spurs not visible as preserved (apparently owing to leg orientation); metabasitarsus length 2.7 mm, width 1.7 mm, with auricle preserved; arolia and claws not visible as preserved; metasoma length 9.0 mm, height 4.5 mm, covered with short setae. See Nel and Petrulevičius (2003) for original description.

Comments.

The fossil was first described as Oligoapis beskonakensis by Nel and Petrulevičius (2003). The specimen is remarkably similar to extant Bombini in terms of its habitus and wing venation. However, the authors decided to place it in a separate genus of an undetermined corbiculate tribe owing to its pterostigma smaller than the prestigma, and by the putative absence of metatibial spurs. The absence of metatibial spurs is merely due to the lack of preservation and not to the definitive absence of spurs, and therefore this character cannot be evaluated. The metatibia is preserved with its outer surface exposed and the presence of spurs (particularly if they were reduced in size) on the inner anterior angle could not be observed in this orientation. In extant species of Mendacibombus , females are characterized by a few long bristles emerging from the outer surface of the metatibia, by a metatibia with the outer surface imbricate, i.e. coarsely sculptured, as well as by an unusually short (i.e., for Bombus s. l.) process of the proximal posterior corner of the metabasitarsus ( Williams et al. 2008, 2016). In the fossil, the long bristles emerging from the outer surface of the metatibia are not visible, while the short process of the proximal posterior corner of the metabasitarsus appears to be present. Furthermore, it is challenging to assess if the metatibia outer surface is coarsely sculptured due to the taphonomy of the specimen.

We consider the fossil as a stem group within Mendacibombus and thus synonymize Oligoapis under that subgenus. Like Oligoapis , Mendacibombus has a relatively reduced pterostigma, further emphasizing the similarity between these groups. Interestingly, this species from the Oligocene-Miocene boundary (i.e., 22.5 Ma) comes from a deposit near the estimated Old World origin of this subgenus ( Williams et al. 2016). Because of the overall morphological assessment we place the species as a stem group within Mendacibombus .

Figures

Figure 1. Representative fossil bumble bees A Oligobombus cuspidatus (photograph by Antropov et al. (2014)) B Holotype of Calyptapis florissantensis (photograph by Manuel Dehon) C C. florissantensis (photograph by Talia S. Karim) D Bombus (Paraelectrobombus) patriciae (photograph by Gaelle Doitteau) E B. (Mendacibombus) beskonakensis (photograph by Gaelle Doitteau).

Figure 3. Forewing drawings of the fossil bumble bees studied herein. Some forewings were mirrored to enable comparison across all specimens A Oligobombus cuspidatus (mirrored) B Holotype of Calyptapis florissantensis (mirrored) C C. florissantensis D Bombus (Paraelectrobombus) patriciae (mirrored) E B. (Mendacibombus) beskonakensis F B. (Cullumanobombus) trophonius (mirrored) G B. (Cullumanobombus) randeckensis (mirrored) H B. vetustus I B. (Cullumanobombus) pristinus (mirrored) J B. (Melanobombus) cerdanyensis.