Agathomyia eocenica Tkoč, 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 : 34-36

Agathomyia eocenica Tkoč , sp. nov.

Figures 30 , 31 zoobank.org/ AD4A9FE2-B217-444B-84BA-770423E2F470 Etymology. The specific epithet, a Latin adjective, refers to the geologic epoch (Eocene) in which this species lived.

Holotype. Agathomyia eocenica Tkoč , female; NMNH, USNM 553697 .

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

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

Differential diagnosis. This species has the typical wing shape and wing venation of Agathomyia , i.e., it has seven longitudinal veins (Sc, R 1, R 2+3, R 4+5, M 1+2, M 4, CuA+CuP), two crossveins (r-m, dm-m) and three non-costal cells are present (rm, bm, cua). Body and legs are dark brown in color; head and abdomen are black to gray; wing with microtrichia, M 1+2 not forked; antenna with first flagellomere conical and several basal aristomeres; tarsomeres of hind leg broad, tarsomere I the longest, both tarsomere II and III wider than long.

Description

Female (Figure 30.1), body dark brown, body length, 4.4 mm, wing length 3.6 mm.

Head. Dark brown, 0.49 mm long, 0.87 mm high (Figure 31.4). Labellum 0.31 mm long, setose with setae approximately 50 μm long; first flagellomere 0.15 mm long, conical, with maximum width 0.10 mm, narrowed apically with three basal aristomeres approximately 50 μm x 30 μm (L x W). Arista not preserved. Proboscis and palpus light brown.

Thorax. Length, 1.51 mm; 4 notopleural setae (two short, two long) visible, one long prescutellar dorsocentral seta and one supraalar seta.

Wing. Length, 3.6 mm, at the middle, width 1.3 mm, with microtrichia (Figure 30.2). First longitudinal vein (R 1) devoid of any spines. Costal cell (c) a little longer than portion of C on subcostal cell (sc), 1.26: 1.10 mm. Length of discal cell (d) 1.55 mm, cell cup, 0.89 mm, bm, 0.57 mm, and rm, 0.77 mm. Plane of crossvein r-m intersects cell c at 59% of its 1.26 mm length. Posterior crossvein (dm-m) almost twice as long (0.34 mm) as distal part of M 4, 0.20 mm. Cell cua elongated, its length about three times portion of vein (CuA+CuP) beyond it.

Legs. Legs dark brown (Figure 31.2-3). Front coxa with long setae. Apex of front femur and basal parts of tibia (= “knees”) of lighter color. Setation of front and middle legs not visible. Visible hind tarsomeres slightly flattened, with dark bifurcated setae (an apomorphic character for family Platypezidae , see Tkoč et al. [2017]).

Abdomen and genitalia. Length, 2.63 mm long, maximum height 0.76 mm; abdominal segments narrowed gradually towards apex, T6–T7 with a row of erect blackish setae at posterior margin (Figure 31.1), approximately 0.13 mm in length (margins of the more anterior tergites not visible). Setae of two basal segments not visible. Cercus 0.16 mm in length, 43 μm in height.

Allotype. Male unknown.

Syncompressions. Diptera (1).

Remarks

The family Platypezidae , with the other flies in Platypezoidea, is thought to be sister to all other Cyclorrhapha ( Wiegmann et al., 2011). Within the Platypezoidea, the family is sister to the clade ( Opetiidae + Microsania ) ( Tkoč et al., 2017). The family is relatively small, with more than 250 extant species in 17 extant genera ( Tkoč et al., 2017). The Paleobiology Database reports 17 fossils of Platypezoidea, most of which from the early Cretaceous ( Mostovski, 1996). Evenhuis (1994) listed 11 species of Platypezidae (including Opetiidae ) in nine genera. Amorim et al. (2018) have recently updated the positions of the Cretaceous biota. Four platypezid fossils are Eocene in age: Two species have been described from the Green River Formation ( Callomyia hypolitha Cockerell, 1909 and C. torporata Scudder, 1890 ), one species from the Florissant ( Eucallimyia fortis Cockerell, 1911 ) and Oppenheimiella baltica Meunier, 1893 from Baltic amber.

The specimen Agathoymia eocenica sp. nov. from the Kishenehn Formation is the first described extinct species of Agathomyia . Its inclusion into any Agathomyia species group is, however, problematic. Some of the important characters required to establish its position within the genus (exact colouration, color of setae on tergites 1–2, setation on middle tibia) are not preserved in the fossil. Figure 30.3 provides a comparison with the recent species Agathomyia antennata ( Zetterstedt, 1819) . The venation is very similar to this species, but there are observable differences: 1) cell cua is more elongated in A. eocenica ; 2) the anal lobe has a different shape; 3) the cell between M 4 and CuA+CuP is narrower and not lobate posteriorly in

A. eocenica ; 4) the costal cell (c) is slightly longer than the portion of costa on subcostal cell (sc) in A. eocenica .

Figures

FIGURE 30. Agathomyia eocenica sp. nov., USNM 553697. 1, Habitus; 2, Left wing; 3, Wing of extant species Agathomyia antennata. Scale bars equal 2.0 mm (1) and 1.0 mm (2). Inset: Apical terminus of R4+5 at costa (right wing).

FIGURE 31. Agathomyia eocenica sp. nov., USNM 553697. 1, Terminal part of abdomen; 2, Legs. Arrows point to three tarsi of the front and middle legs; 3, Hind leg; 4, Head. Long arrow denotes apical marginal setae of the pedicel, short arrow denotes several basal aristomeres – the terminal aristae are missing. Inset: Labellum with postero-ventral setae. Scale bars equal 0.5 mm (1), 1.0 mm (2) and 0.25 mm (3, 4).