Hoplocyrtoma eocenica Sinclair and Greenwalt, 2022

Greenwalt, Dale E., Amorim, Dalton De Souza, Hauser, Martin, Kerr, Peter H., Fitzgerald, Scott J., Winterton, Shaun L., Cumming, Jeffrey M., Evenhuis, Neal L. & Sinclair, Bradley J., 2022, Diptera of the Middle Eocene Kishenehn Formation II, Palaeontologia Electronica (a 22) 25 (2), pp. 1-52 : 35-37

Hoplocyrtoma eocenica Sinclair and Greenwalt sp. n.

Figures 20-21

zoobank.org/ B9FBCA7E-96C1-4702-AD62-AFCFA2813778

Type species. Cyrtoma procera Loew, 1864b (original designation)

Holotype. Female, USNM 621518 , deposited in the Department of Paleobiology , National Museum of Natural History ( NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Locality and horizon. Park site, Middle Fork of the Flathead River (Pinnacle, Montana, USA). Middle Eocene Coal Creek Member, Kishenehn Formation.

Etymology. The specific epithet refers to this species occurrence in the Eocene period.

Diagnosis. Hoplocyrtoma eocenica is identified as belonging to Hoplocyrtoma due to a combination of C ending at R 4+5, M forked and evanescent – weakest at base, cell dm absent, CuA and cell cu a present, anal lobe well developed and hind femur enlarged, hind leg raptorial.

Description (female). Dorsolateral aspect ( Figure 20A ). Body length 2.15 mm, (left) wing shorter than body, 1.81 mm x 0.79 mm; ratio of wing length to body length = 0.84; head dark brown/black, thorax black, abdomen brown. Head oval, approximately 0.39 mm in diameter; palpus 3 times as long as broad, 0.12 mm long; pedicel suboval, approximately 50 μm long, with row of short setae at apical border; postpedicel conical, gradually tapered, 165 μm long, 60 μm maximum width; stylus 105 μm in length ( Figure 21A ). Thorax approximately 0.75 mm long, at least one pair of long bristles at apex of scutellum. Wing (right) 2.3 times long as wide, 1.81 mm long, 0.79 mm wide; covered with microtrichia; costa with short setae, terminates at R 4+5, setae longer along the posterior margin of wing and along well-developed anal lobe; Sc light, close to and parallel to R 1, fading away at proximal end of pterostigma; R 1 ending in C ¾ of the length of wing, pterostigma anterior to and along the distal half of R 1; C, R 1, R 2+3 and R 4+5 more heavily sclerotized, than other longitudinal veins, though all weaker at base of wing; R 2+3 straight, R 4+5 gently sinuous, with both veins broadly divergent at wing margin. M nearly absent at mid-wing, forked into evanescent M 1 and M 2, both of which reach wing margin. Cross vein r-m origin just distal to R 1 fork, cell br shorter than cell bm, cell bm longer than cell cua, cell dm absent; M 4 reaching wing margin; CuA recurrent, stronger at base, reaching CuA+CuP; CuA+CuP very weak, possibly not reaching wing margin ( Figure 20 B-C). Fore tarsus and hind legs preserved. Hind leg raptorial, femur enlarged, length and width 0.79 and 0.20 mm, respectively; width to length ratio = 0.25. Hind femur darkly pigmented on dorsal surface, light brown elsewhere, with two interspersed rows of short stout spines and thinner, longer setae on ventral surface. Hind tibia geniculate at base, much shorter than corresponding femur, 0.59 mm long, 80 μm wide just below bend, 117 μm at apex; tarsus 0.59 mm long ( Figure 21B ). Abdomen excluding genitalia, 1.15 mm long, setae present along apical surface of at least tergite 2. Abdomen terminating in pair of elongate cerci; cercus thin, approximately 0.14 mm long ( Figure 21C ).

Male. Unknown.

Synimpressions. One Hymenoptera (Parasitica)

Remarks. Given the age of the Empidoidea – fossils from the Jurassic are known and evidence suggests that extant families and subfamilies were well established by the Early Cretaceous ( Grimaldi and Cumming, 1999; Grimaldi and Engel, 2005) – and the unique and readily recognizable morphology of members of Bicellariinae , the absence of this family from the fossil record up to this point is surprising. Hoplocyrtoma eocenica is the first known fossil of the subfamily, a monophyletic clade suggested by Sinclair and Cumming (2006) as Bicellariini , to be sister to Hybotinae . Wahlberg and Johanson (2018) elevated this lineage to subfamily rank and assigned it as sister to all other Hybotidae based on molecular phylogenetic analysis. The subfamily contains three genera, Bicellaria Maquart, 1823 , Hoplocyrtoma and Leptocyrtoma Saigusa, 1986 , all of which are characterized by an unique wing venation that includes cell dm absent and the branches of M evanescent, especially at their base. Both Bicellaria and Leptocyrtoma are defined, in part, by the absence of enlarged raptorial hind legs, a distinguishing feature of Hoplocyrtoma ( Melander, 1928; Saigusa,1986). Melander (1928) stated: “The hind femora are swollen and abundantly armed beneath with a mixture of spines and thorns. The hind tibiae are much shorter than the femora, not clavate but nearly straight and cylindrical, geniculate at the knee”.

Hoplocyrtoma eocenica is differentiated from the four extant species in the genus, H. japonica Saigusa and Kato, 2002 , H. watanabei, Saigusa and Kato, 2002 , H. procera Loew, 1864b and H. femorata Loew, 1864b , as follows: the former three species are characterized by having the postpedicel sharply attenuated apically, whereas the postpedicel in H. femorata and H. eocenica is gradually

PALAEO- ELECTRONICA.ORG tapered. Hoplocyrtoma eocenica is much smaller than H. femorata , with a wing length of more than 4.0 mm in the latter species.

Figures

FIGURE 20. Hoplocyrtoma eocenica Sinclair and Greenwalt sp. n., USNM 621518, female. A, Habitus; B, Left wing; C, Left wing, drawing. Scale bars equal 2.0 mm (A) and 1.0 mm (B).

FIGURE 21. Hoplocyrtoma eocenica Sinclair and Greenwalt sp. n., USNM 621518. A, Antennae and mouthparts; B, Left hind leg; C, Genitalia. Scale bars equal 0.2 mm (A, C) and 0.5 mm (B).