Microburmyia Grimaldi & Cumming

Grimaldi, David A., Arillo, Antonio, Cumming, Jeffrey M. & Hauser, Martin, 2011, Brachyceran Diptera (Insecta) in Cretaceous ambers, Part IV, Significant New Orthorrhaphous Taxa, ZooKeys 148, pp. 293-332 : 309-310

Microburmyia Grimaldi & Cumming gen. n.

Diagnosis.

R1 long, apex reaching to 2/3 length of wing; R1 branching off of the stem of R quite distad, R2+3 long, branching off of Rs in the distal half of the wing; cells br and bm large, length nearly half that of wing; M1+2 forked; vein A1 either incomplete or absent. Mesoscutum strongly arched; it and abdominal tergites devoid of bristle-like setae or long pilosity; apical tibial spurs lacking. Body size minute, ca. 1.0 mm in length.

Type Species.

Microburmyia analvena , sp. n. By present designation

Etymology.

Derived from micro- (L.), minute; -burm-, Burma; and -myia (Gr.), fly, in reference to the minute body size and provenance of this brachyceran. Feminine.

Discussion.

The family placement of the two new species in this genus is not entirely certain, particularly since in mythicomyiids vein R2+3 is typically short and its apex fused with R1. The genus is placed in the Mythicomyiidae since the venation bears a resemblance to the Baltic amber genus Carmenelectra Evenhuis ( Evenhuis 2002), though differing from that Baltic amber genus by R1 branching off of the stem of R quite distad (vs. near the base of the wing), R2+3 branching off of Rs in the distal half of the wing (vs. in the basal half), and by crossveins r-m and cu-m being in line (vs. stepped). Other features of Microburmyia that are consistent with mythicomyiids are the strongly arched scutum, structure of apical antennal articles (with minute stylus in Microburmyia analvena , ovoid first flagellomere in Microburmyia veanalvena ), incomplete Sc vein, palpi minute or absent, and the minute body size. Microburmyia is plesiomorphic with respect to all other known mythicomyiids (cf., Evenhuis 2002).

Mythicomyiidae are traditionally (e.g., Hall 1981) and phylogenetically (e.g., Yeates 1994; Woodley 1989; Woodley et al. 2009) placed as the sister group to the Bombyliidae s.s, often classified as a subfamily, but also as a separate family (e.g., Evenhuis 2002). There is strong morphological and molecular support for Bombyliidae + Mythicomyiidae being the sister group to the rest of Asiloidea ( Woodley 1989; Yeates 2002; Wiegmann et al. 2011) or the sister group to the rest of Asiloidea and Eremoneura ( Sinclair et al. 1994; Trautwein et al. 2010). With the exception of an unforked R4+5 and short or vestigial anal vein in Microburmyia , it is very interesting that its venation is intermediate between that of the Hilarimorphidae and the more specialized venation of mythicomyiines. This would lend support to the hypothesis that Hilarimorphidae is the sister group to the Bombyliidae ( Woodley 1989; Yeates 1994; Woodley et al. 2009). Another hypothesis places the Hilarimorphidae (sometimes including the enigmatic and monotypic genus Apystomyia Melander 1950) as the sister group to the Eremoneura (Yeates, 2002) (see also discussion under Apystomyidae , vide infra). Oddly, the recent total-evidence phylogeny of flies placed the Hilarimorphidae (excluding Apystomyia ) as sister group to the Acroceridae ( Wiegmann et al. 2011), for which there is very limited molecular and no morphological support, although this result does suggest a position of Hilarimorphidae distant from Eremoneura.

Lastly, it is interesting to note that the fossil record of Bombyliidae s.s., exclusive of mythicomyiines, is entirely Tertiary. Bombyliidae is a large, cosmopolitan family (ca. 4,500 species) of flies that are most diverse in xeric ecosystems, where they are important pollinators of herbaceous plants. Their fossil record in sedimentary matrices and in amber (Baltic, Dominican) is quite diverse for North America and Europe ( Evenhuis 1994), suggesting that the bombyliids s.s. radiated rapidly in the early Tertiary.