Drapetis adelomedos Greenwalt, 2019

Dale E. Greenwalt, Daniel J. Bickel, Peter H. Kerr, Gregory R. Curler, Brian V. Brown, Herman de Jong, Scott J. Fitzgerald, Torsten Dikow, Michal Tkoč, Christian Kehlmaier & Dalton De Souza Amorim, 2019, Diptera of the middle Eocene Kishenehn Formation. I. Documenting of diversity at the family level, Paleontologia Electronica 22 (2), No. 50, pp. 1-56 : 33-34

Drapetis adelomedos Greenwalt , sp. nov.

Figures 28 , 29 zoobank.org/ A993F24D-BC6A-4035-B36A-02E3DFE65FE1 Etymology. The specific epithet is derived from the Greek words adelos (obscure) and medos (plan) and references the lack of preserved morphological detail of the genitalia.

Holotype. USNM 621705 , deposited in the Department of Paleobiology , National Museum of Natural History (NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Type horizon. Middle Eocene Coal Creek Member, Kishenehn Formation.

Type locality. Tunnel Creek site, Middle Fork of the Flathead River (Pinnacle, Montana, USA).

Differential diagnosis. Antenna with long terminal arista-like stylus, pedicel with marginal setae but without visible ventral bristle; proboscis stronger at

base. One pair of vertical bristles visible on head. Rs longer than bm-cu cross vein, cell br much shorter than cell bm, cell dm absent, and radial and medial veins not forked; cup absent/not visible, CuP very weak. Scutum about as long as broad.

Description

Male. (Figure 28.1). Length, including terminalia, 2.5 mm.

Head. (Figure 29.1-2). Black/dark brown, spherical, diameter 0.4 mm, dark. Proboscis subtriangular in shape, 0.22 mm in length, 0.12 mm wide at base, heavily setose at base. Antennae reddish brown, 0.52 mm in length with apically concave pedicel with marginal fringe of short setae; first flagellomere triangular, concave at base, 90 μm long, 67 μm wide, L/W = 1.35. Arista 0.35 mm long, covered with short setae, approximately 8 μm in length. Head with one pair of occipital bristles, about 0.1 mm in length.

Thorax. Redish, 0.73 mm long, scutum barely longer than wide, as long as head.

Wings. (Figure 28.2-3). Length, 1.75 mm (right), width 0.8 mm; hyaline; microtrichia arranged in parallel longitudinal lines; costal setulae well developed; Rs about one-third length of cell bm, longer than bm-cu cross vein, cell br length about half that of cell bm; R 2+3 strongly arched upwards, extending to beyond midlength of wing, R 4+5 slightly sinuous, barely divergent from M 1+2; crossvein r-m nearly transverse, dm-m less so.

Legs. Forelegs and middle legs not preserved; hind femur with row of several short weakly sclerotized posteroventral bristles (Figure 29.3); hind tibia 0.52 mm long, 0.12 mm wide, with posteroventral row of stout bristles, about 0.06 mm in length. Hind tarsus 0.75 mm in length, 1 st tarsal segment longest, 0.34 mm long.

Abdomen and genitalia. 1.37 mm in length, reddish/dark brown. Details of the male genitalia not preserved.

Allotype. Female unknown.

Syncompressions. None.

Remarks

The family Hybotidae consists of 2,005 species in 75 genera. It contains 48 described fossils, most (27) of which are from the Eocene. The genus Drapetis was originally separated into two subgenera, Drapetis and Crossopalpus Bigot, 1857 , by Melander (1918), but the two are now recognized as separate genera. Crossopalpus , which contains 34 species, is distinguished by the pedicel with a distinct ventral bristle. Drapetis , with 156 extant species, is represented in the fossil record by six species, five in Baltic amber ( Meunier, 1908) and one, D. dissentis Solórzano Kraemer et al., 2005 , from Miocene Chiapas amber. The Chiapis specimen and the Baltic amber species described by Meunier are all smaller than D. adelomedos , ranging from 0.75 to 1.75 mm in length. Other differences exist. Drapetis brevis Meunier, 1908 has a subapical arista and r-m and m-cu nearly touching. In our view, this specimen does not belong to Drapetis and is here designated as Hybotidae undetermined. Drapetis decolorata Meunier, 1908 has cell bm triangular in shape, with origin of m-cu cross vein at the level of the Rs fork. D. vitiosum Meunier, 1908 has m-cu origin much closer to the level of the Rs fork than the R 1 terminus. However, CuP of Drapetis , when present, is weak, faint and concave (absent in D. adelomedos ) whereas CuP in D. vitiosum is figured by Meunier as strong and distinctly convex. Drapetis vitiosum does not appear to belong to Drapetis and is here designated as Hybotidae undetermined. Drapetis decoratum Meunier, 1908 , has a single apical tibial spine. Its wings were not figured by Meunier, who described them as “a little longer than the body and quite wide. Length = ¾ mm.” Given the absence of a detailed description of the venation, these specimens (both the male and female were described) must be re-examined before they can be reliably assigned to the genus Drapetis . Drapetis mortuum Meunier, 1908 , has F1 convex at its base and an L/ Wmax ratio = 2.2 (vs. 1.3 for Drapetis sp.). Drapetis dissentis differs from D. adelomedos in that its R 4+5 is strongly divergent from M 1+2.

Figures

FIGURE 28. Drapetis adelomedos sp. nov., USNM 621705. 1, Habitus; 2, Right wing. Arrowhead and arrow denote r-m and m-cu cross veins respectively; 3, Line drawing of wing. Scale bars equal 2.0 mm (1) and 0.5 mm (2).

FIGURE 29. Drapetis adelomedos sp. nov., USNM 621705.1, Antennae. Arrow denotes a row of setae at the apical margin of the pedicel and arrowheads point to setae on the arista; 2, Head. Arrow denotes two occipital bristles. Arrowhead points to setae at base of proboscis; 3, Hind leg and terminalia. Arrowhead points to posteroventral femoral spines; four small arrows denote short setae on the hind femur; large arrow points to the claws. Scale bars equal 0.25 mm (1), 0.2 mm (2, 3).