Dixella eomarginata Greenwalt and Moulton

Greenwalt, D, 2016, The first fossil New World Dixidae with a critical discussion of generic definitions, Palaeontologia Electronica 19 (3), pp. 1-32 : 7-8

Dixella eomarginata Greenwalt and Moulton , new species

Figures 3.2 , 6 , 7

zoobank.org/ 0EC67728-2799-4615-B318-3723C944DE99

Etymology. The specific epithet is a combination of the Greek term eos, meaning dawn, and the specific epithet marginata , indicating similarity of the shape of the posterior margin of the wing with that of the extant Dixella marginata Loew, 1863 .

Holotype. Dixella eomarginata Greenwalt and Moulton , female; NMNH, USNM 553521 .

Type Horizon. Middle Eocene Coal Creek member, Kishenehn Formation.

Type Locality. Dakin site, Middle Fork of the Flathead River (Pinnacle, Montana) .

Differential Diagnosis. Distinguished from all other fossil Dixidae based on the presence of the following character states: wing emarginate between CuA1 and CuA2, wing length to body length ratio equal to 0.91, R 1 closer to C than R 2.

Description. Adult female ( Figure 6 ), body length 3.8 mm.

Head. Black. Eyes dichoptic, spherical, diameter 0.26 mm, 0.12 mm. Maxillary palps not visible. Antennae not preserved intact, contiguous flagellomeres present, brown, filiform. Pedicel light brown, longer than wide. One maxillary palp present, poorly preserved, length 0.5 mm; length terminal segment 0.179 mm.

Thorax. Lateral view. Length 1.03 mm, black; lateral vittae absent; scutellum brown. Thoracic setae not visible.

Wings. Length 3.46 mm (measured from base of humeral crossvein), width 1.18 mm ( Figures 3.2 , 7.1 ). L/W ratio = 2.93. Vein R 2+3 arched. Vein Sc apex basal to origin of Rs (1.4 times distance between C, R1). Crossvein r-m basal to Rs bifurcation. Crossvein m-cu very lightly sclerotized, apex just distal to r-m terminus. A1 apex poorly preserved, basal to Cu bifurcation, distal to Sc apex. R 2+3 bifurcation significantly basal to M bifurcation. Ratios R 2 /M 2, M 2 /M 1, M 2 /M 1+2, R 2+3 /R 3 = 2.37, 0.71, 0.55, 0.44, respectively. Wing veins, margin with thin setae, length ≤ 20 μm. Wing posterior margin emarginate between CuA1, CuA2. Prominent false vein (?) between M, Cu continues between M 1+2,

GREENWALT & MOULTON: NEW WORLD FOSSIL DIXIDAE

CuA 1 (not present in the right wing). Haltere brown, length 0.53 mm long, knob oval, width 144 μm, length wide 207 μm.

Legs. All legs setose; metatibia expanded distally. Foreleg femur, tibia, tarsus lengths 1.28, 1.29, 1.65 mm, respectively. Midleg femur, tibia, tarsus lengths 1.71, 1.40, 1.78 mm, respectively. Hind leg femur, tibia, tarsus lengths 1.65, 1.56, 2.22 mm, respectively. Metapretarsal claws not preserved sufficiently to determine presence, absence of teeth.

Abdomen and genitalia. Abdomen light brown, length 2.66 mm (not including cerci). Segment 7 with single sclerotized spermatheca, oval, 154 μm x 115 μm. Tergite 9, posterior edge sternite 8 dark brown/black, more heavily setose than anterior portions of abdomen. Cerci dorsally situated, brown, setose, length 0.12 mm ( Figure 7.2 ). Posterior margin sternite 8 lined by numerous setae approximately 35 μm long, Cerci, tergite 9 with several setae 70 μm or longer. Sternite 9 bulbous, protruding just below cerci.

Male unknown.

Figures

FIGURE 3. Line drawings of wings. 1, Dixella intacta; 2, D. eomarginata; 3, D. curvistyla. Wing venation is from McAlpine (1981). Scale bar equals 1 mm.

FIGURE 6. Habitus of Dixella eomarginata, holotype. Scale bar equals 3 mm.

FIGURE 7. Morphological features of Dixa eomarginata. 1, Wing with an emarginate posterior margin (arrowhead); arrows denote an apparent false vein posterior to vein M. 2, Terminalia. Scale bars equal 1.0 mm (1) and 0.25 mm (2).