Eodromyia pumilio, Myskowiak & Garrouste & Nel, 2018

Myskowiak, J., Garrouste, R. & Nel, A., 2018, Eodromyia pumilio gen. et sp. nov., a new empidoid fly from the Earliest Eocene amber of France (Diptera: Hybotidae: Tachydromiinae), Zootaxa 4379 (2), pp. 279-286 : 280-285

Eodromyia pumilio sp. nov.

( Figs 1–4 )

Type material. HOLOTYPE male, labeled: MNHN.F. A57316 ; stored in the Laboratory of Palaeontology , MNHN, Paris, France .

Etymology. Named after its very small size.

Diagnosis. As for the genus. Very small fly, wing 0.9 mm long, 0.4 mm wide.

Type strata. Lowermost Eocene, Sparnacian, level MP7 of the mammal fauna of Dormaal.

Type locality. Le Quesnoy, Chevrière, region of Creil, Oise department, France.

Description. Male. Head triangular in shape from above, 0.2 mm long and 0.15 mm wide; eyes 0.15 mm long and 0.05 mm wide, dichoptic with deep ocular notch ( Fig. 1A ); eyes well separated on frons and linearly approximate on face, with ommatrichia; ocellar triangle broad and shallow, with 2 pairs of ocellar setae, anterior pair just behind anterior ocellus, convergent, posterior pair divergent; postocellar setae minute and proclinate; inner vertical long and divergent; a series of four rather long pairs of setae on occiput; gena very shallow. Antenna with very small, bare scape, pedicel setose with row of short setae surrounding apex, wider than postpedicel, subequal in length with suboval postpedicel; length of postpedicel ca. 0.05 mm; flagellum aristate, apex of flagellum with bristle-like style; flagellum 0.15 mm long. Mouthparts well developed, distinctly shorter than head; maxillary palpus not visible; sclerotized sharp and dark structure (hypopharynx?).

Thorax 0.3 mm long, 0.25 mm wide; scutum as broad as long; 6 pairs of presutural acrostichal setae and 6 presutural dorsocentral setae; lateral portion of thorax poorly visible, but mesopleuron with some setulae; scutellum with single apical pair of setae.

Wing 0.9 mm long and 0.4 mm wide, slender, W/L = 0.44 ( Figs 1B , 2B ); membrane microtrichia arranged in oblique rows and longitudinal rows; vein C reaching apex of M; Sc short, very faint [best seen when tilting specimen]; base of vein R thick; R1 short, 0.35 mm long; Rs originating well distal to level of crossvein h, rather long, 0.2 mm long, weaker than R2+3 and R4+5; R2+3 unbranched, slightly curved anteriorly, meeting C 0.4 mm from wing base; R4+5 slightly curved anteriorly, meeting C 0.6 mm from wing base; distance between apices of R2+3 and R4+5 twice that between R2+3 and R1; first sector oblique; crossvein r-m short, perpendicular to R4+5 and M; vein M simple, complete, unbranched, nearly straight, extended to tip of wing; CuA simple (CuA2 lost, no cells bm and cup), weakly curved posteriorly, reaching wing margin; M and CuA strongly divergent; bm-cu, dm-cu and A1 veins lost; anal lobe present but narrow; alula not developed. Halter not visible.

Legs of moderate length, setulose, without distinctive spines/spurs; femora, especially fore femur, very broad compared to tibiae, fore femur 0.25 mm long, 0.15 mm wide; median femur 0.25 mm long, 0.05 mm wide; hind femur 0.35 mm long, 0. 0 5 mm wide, without subapical strong setae; fore tibia appressed to femur, gland not viewable; median tibia 0.35 mm long; hind tibia 0.5 mm, bearing anterodorsal setae; pretarsus with claws well developed, empodia setiform, pulvilli present.

Abdomen 0.8 mm long, 0.25 mm wide, relatively short compared to wings, with sparse vestiture of short, stiff setae; male genitalia visible, asymmetrical, only epandrium and surstyli discernable ( Fig. 4C).

Female. Unknown.

Discussion. Eodromyia gen. nov. can be attributed to the Empidoidea on the basis of the following characters: ptilinal fissure absent; empodia setiform; three flagellomeres; CuA2 absent; flagellum elongate; wing rounded at apex; A1 not reaching wing margin; Sc incomplete ( Buck et al. 2009). Eodromyia gen. nov. is similar in wing venation to the Cretaceous empidoid atelestid genus Cretodromia Grimaldi & Cumming, 1999 and the genus Myanmyia Grimaldi et al., 2011 ( Diptera : unplaced family) due to the complete reduction of CuA2, no cell bm, and all longitudinal veins simple ( Grimaldi & Cumming 1999; Grimaldi et al. 2011). Despite the somewhat similar venation of these two Cretaceous fossils, Eodromyia gen. nov. belongs to the tribe Drapetini [= Drapetidini] Collin, 1961 ( Hybotidae Tachydromiinae ) as defined by Sinclair & Cumming (2006) by sharing the following synapomorphies: apex of antenna with long, slender seta-like receptor; R4+5 unbranched; loss of M2; loss of cell dm, due to loss of dm-cu; eyes with ommatrichia (even if some other Empidoidea also have ommatrichia); loss of CuA2. Chillcott & Teskey (1983) added that the Drapetini are recognized by the scutum being as broad as or broader than long, which is also the case in Eodromyia gen. nov.

Drapetini comprises 19 genera ( Sinclair & Cumming 2006; Cumming 2006), viz. Allodromia Smith 1962 , Atodrapetis Plant, 1997 , Austrodrapetis Smith, 1964 , Austrodromia Collin, 1933 , Chaetodromia Chillcott, 1983 , Chersodromia Walker , Crossopalpus Bigot, 1857 , Dusmetina Gil Collado, 1930 , Drapetis Meigen, 1822 , Elaphropeza Macquart, 1827 , Isodrapetis Collin, 1928 , Megagrapha Melander, 1927 , Micrempis Melander, 1927 , Nanodromia Grootaert, 1994 , Ngaheremyia Plant & Didham, 2006 , Pontodromia Grootaert, 1994 , Sinodrapetis Yang, Gaimari & Grootaert, 2004 , and Stilpon Loew, 1859 . Cumming (2006) also added the genus Baeodromia . Eodromyia gen. nov. differs from all these genera in the absence of crossvein bm-cu. But this character alone is not sufficient to accurately separate Eodromyia gen. nov. from the extant taxa. Dusmetina has micropterous wings ( Gil Collado 1930), but this character alone is not sufficient to separate it from Eodromyia gen. nov. as some degree of wing reduction is also known to occur in peculiar species of some other tachydromiine genera, viz., Stilpon ( Smith 1969) or Platypalpus ( Grootaert & Shamshev 2008; Freitas-Silva & Ale-Rocha 2013). Dusmetina differs from Eodromyia gen. nov. in the presence of strong subapical spines on hind femora.

Austrodrapetis shows some similarities with Eodromyia gen. nov. in the venation, viz. shortened R1, and R2+3 and R4+5 curved, but in the former genus R2+3 is shortened, and its basal part of Rs aligned with basal part of R4+5, and it has also only one pair of strong dorsocentrals ( Smith 1964). Baeodromia has a shortened R2+3, but a very short posterior pair of ocellar setae (Cumming 2006). Atodrapetis has R2+3 and R4+5 separating at the same point, aligned with r-m, plus an apical arista-like stylus and no pair of minute setae behind the posterior ocelli ( Plant 1997). Nanodromia and Pontodromia have a very short R1 distal of base of Rs ( Grootaert 1994). Austrodromia has CuA1 more straight than in Eodromyia gen. nov., its R2+3 is more weakly curved than in Eodromyia gen. nov., and also its eyes are narrowly separated on the frons ( Collin 1933; Chillcott & Teskey 1983). Chaetodromia has a rather straight R2+3 and two pairs of vertical bristles, unlike Eodromyia gen. nov. ( Chillcott & Teskey 1983).

Chaetodromia , Megagrapha , Sinodrapetis , Micrempis , Isodrapetis , Elaphropeza , and Chersodromia have a straight R4+5, subparallel with M, but this character can be variable within some genera ( Melander 1928; Chillcott & Teskey 1983; Plant 1999; Grootaert & Shamshev 2012). Eodromyia gen. nov. and Elaphropeza differ from Drapetis in the presence of antero-dorsal setae on hind tibiae, but Eodromyia gen. nov. has venation rather similar to that of Drapetis ( Smith 1962; Chvála 1975; Yang et al. 2004a). Crossopalpus has no anterior pair of ocellar setae ( Yang et al. 2004b). Stilpon has no prominent bristles on the hind tibia, and a linear frons unlike Eodromyia gen. nov. ( Shamshev & Grootaert 2004). Crossopalpus and Elaphropeza have their mesopleuron lacking setulae, unlike Eodromyia gen. nov. ( Rogers 1983). Eodromyia gen. nov. also differs from Micrempis and Isodrapetis in the arista-like stylus subapical and somewhat dorsal ( Chillcott & Teskey 1983; Plant, 1999). Eodromyia gen. nov. differs from Megagrapha in the present of distinct setae on the ocellar triangle ( Chillcott & Teskey 1983). Eodromyia gen. nov. differs from Chersodromia in the R2+3 distinctly longer than R1 ( Grootaert & Shawshev 2012), and differs from Ngaheremyia in the presence of a series of four rather long pairs of setae on the occiput, instead of a few weak setae ( Plant & Didham 2006). Eodromyia gen. nov. differs from Allodromia and Sinodrapetis in the complete absence of an anal vein close to the posterior wing margin ( Smith 1962; Yang et al. 2004c).

Sinclair & Cumming (2017) mention two undescribed drapetine genera from the Afrotropical Region and indicate that their Undescribed Genus A also lacks vein CuA2 and has no cell bm. This genus however lacks a vertical r-m crossvein ( Sinclair & Cumming 2017, fig. 6) unlike Eodromyia gen. nov.

The Oligocene genus Archaeodrapetiops Martins-Neto et al. 1992 , considered by the authors to be related to Drapetis and Elaphropeza , strongly differs from Eodromyia gen. nov. in the presence of a long crossvein bm-cu very far from r-m. The absence of head characters for this genus, based on incomplete compression fossils renders its family attribution uncertain ( Martins-Neto et al. 1992). It should be noted that Solórzano-Kraemer et al. (2005) listed the Oligocene genus Taubatempis Martins-Neto 1999 among the fossil Tachydromiinae , but Martins-Neto (1999) considered it in the Empididae . This genus is based on very poor compression fossils for which even the attribution to this family is weakly supported.

Concluding remarks. Except for Archaeodrapetiops , all the other fossil taxa currently included in the Drapetini belong to extant genera (Solórzano-Kraemer et al. 2005). The tribe is known from the mid Eocene Baltic amber, and the Miocene Mexican and Dominican amber. Eodromyia gen. nov. is the oldest representative of the tribe, even if it is only a few million years older than Baltic amber. This fossil strongly suggests that the diversification of this group is certainly more ancient.

Figures

FIGURE 1. Eodromyia pumilio gen. et sp. nov., holotype MNHN.F.A57316. A. habitus dorsal view (white arrow: ocular notch); B. wing.Scale bars = 0.4 mm (A); 0.2 mm (B).

FIGURE 2. Eodromyia pumilio gen. et sp. nov., holotype MNHN.F.A57316. A. habitus ventral view; B. drawing of wing. Scale bars = 0.5 mm (A); 0.5 mm (B).

FIGURE 3. Eodromyia pumilio gen. et sp. nov., holotype MNHN.F.A57316. Ventral view of head, arrow: mouthparts. Scale bar = 0.2 mm.