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Rhamphomyia kitadai, Rhamphomyia brunnipennis, Rhamphomyia decens and Rhamphomyia pennipes from Middle Eocene Kishenehn Formation

Rhamphomyia kitadai, Rhamphomyia brunnipennis, Rhamphomyia decens and Rhamphomyia pennipes from Middle Eocene Kishenehn Formation

NEWS - Leland Kitada dance fly (Rhamphomyia kitadai sp. nov.), brown wings dance fly (Rhamphomyia brunnipennis sp. nov.), beautiful dance fly (Rhamphomyia decens sp. nov.) and wing-footed dance fly (Rhamphomyia pennipes sp. nov.) from the Middle Eocene Kishenehn Formation are described as species new to science.

Females of Empidinae often display sexual ornamentation, an adaptation in the animal kingdom in general, often associated with males, especially in vertebrates. Ornamentation of female Empidinae includes legs with rows of relatively large pennate scales, enlarged and/or darkly pigmented wings and an expanded abdominal pouch.

The ornamentation makes the female appear larger, more fertile and therefore more attractive to potential mates. Given the rarity of female sexual ornamentation, especially Empidini, it has become a model system for studying this phenomenon.

The known fossil record includes several genera from the mid-Jurassic era dominated by two genera, Empis and Rhamphomyia, which account for nearly 60% of all fossil evidence and no fossil record of empidine sexual ornamentation other than pennate leg scales.

Dale Greenwalt of the National Museum of Natural History, Smithsonian Institution in Washington, D.C. and Bradley Sinclair of the Canadian National Collection of Insects and the Canadian Food Inspection Agency in Ottawa reviewed this fossil record from the Middle Eocene Kishenehn Formation with enlarged and/or darkly pigmented wings and pennate leg scales.

R. brunnipennis, holotype, female, is given the specific epithet from the Classical Latin brunneus (brown) and pennis (wing) and refers to the pigmentation of the wings of this specimen. Specimen from the Dakin site, Kishenehn Formation, Colorado (USA); Middle Eocene (Lutetian).

Female length 3.46 mm (with cerci). Head 0.64 mm long, brown/black, without observable setae. Antenna black, 0.55 mm long, scape 79 μm long, pedicel 58 μm long, set apically; postpedicel 0.41 mm in length, L/Wmax = 6.8, stylus 66 μm long. Mouthparts not preserved.

Thorax brown/black, 1.18 mm long. Wing with basal portion of anterior edge slightly folded/overlapped, 2.7 mm long, 1.76 mm wide, area 3.5 mm 2 , TAL = 1.3, lw/ww = 1.55; basal sixth of wing hyaline, remainder dark brown; length of cell br > cell bm > cell cua, vein CuA recurved and confluent with underside of cell cua.

Legs black to brown, only portions of four legs preserved, not pennate. Abdomen brown/black, 1.66 mm in length, thorax/abdomen length ratio 0.71, cerci approximately 0.22 mm in length.

R. decens, holotype, female, derived from the Latin decens, meaning attractive or beautiful, and refers to the extensive sexual ornamentation of the species. Specimen from the Disbrow Creek site, Kishenehn Formation, Colorado (USA); Middle Eocene (Lutetian).

Female length (lateral view) 4.5 mm long, black. Head 0.55 mm long, 0.58 mm high, proboscis 0.58 mm long, with setae along ventral surface. Palpi (one behind the other) setose apically, 250 mm long, 45 μm wide. Antenna 0.6 mm long, both scape and pedicel set apically, 0.12 mm and 80 μm long respectively; postpedicel length 0.31 mm long, ratio of L/Wmax = 3.1, style 95 μm long, 20 μm wide.

Thorax black, approximately 1.64 mm long, laterotergite with row of long, dark setae, other setae, possibly postpronotal, notopleural and postalar, also present. Wing poorly preserved, length approximately 2.86 mm, width 1.25 mm, lw/ww = 2.29, length of cell br > cell bm > cell cua, vein CuA recurved and confluent with underside of cell cua.

Legs black, hind femur, tibia and tarsomere 1 enlarged, fore, mid and hind femora and tibiae and hind tarsomere 1 all with pennate scales; lengths and widths (scales not included) of hind femur, tibia and tarsomere 1 approximately 1.45 mm × 0.35 mm,1.57 × 0.22 mm, and 0.64 mm × 0.13 mm, respectively. Abdomen 2.45 mm in length, cerci setose, relatively small, approximately 0.25 mm long.

R. kitadai, holotype, female, named in honor of Leland Kitada who joined the Peace Corps to teach because his ethnicity prevented him from pursuing a career as a science teacher in the United States. Specimen from Disbrow Creek site, Kishenehn Formation, Colorado (USA); Middle Eocene (Lutetian).

Female length about 3.5 mm. Head 0.42 mm long, 0.49 mm high, dark brown, without observable setae. Antenna brown, 0.52 mm long, scape set apically, pedicel not preserved, stylus 64 μm long with apical process 20 μm × 8 μm wide; proboscis brown, setose, relatively short, 0.33 mm long, 0.14 mm wide at base; palpus 0.2 mm long, 50 μm in width, set apically. Thorax dark reddish brown, 1.06 mm in length, not preserved/visible.

Legs mostly brown, coxae and base of at least hind femur pale, not pennate, hind femur 0.92 mm long, 0.17 mm wide, heavily setose, hind tibia 1.09 mm long × 0.11 mm wide and hind tarsus 1.12 mm long, 90 μm wide (T1). right wing 2.7 mm long × 1.6 mm wide, area 3.6 mm2 , apparent wing area/thorax + abdomen length (TAL) = 1.3 (both wings); r4+5 unbranched, cells bm and dm incompletely preserved, M 2 /d = 1.8, lw/ww = 2.1.

Abdomen brown with intersegmental areas unpigmented, 2.1 mm in length, hind marginal setae on all tergites; ratio of thorax/abdomen lengths = 0.5. Cerci 175 μm × 33 μm, setose.

R. pennipes, holotype, female, is given the specific epithet from the Latin pennipes (winged-footed) and refers to the segmented scales on the hind legs of this specimen. Specimen from the Park site, Kishenehn Formation, Colorado (USA); Middle Eocene (Lutetian).

Female length (ventral view) 2.86 mm. Head dark brown, 0.33 mm long, 0.37 mm high, setae visible at dorsal base of proboscis and ventral portion of head; proboscis 0.33 mm long. Neither scape nor pedicel completely visible, right postpedicel set basally, length (from bulbous base) 0.26 mm, ratio of L/Wmax = 4.4.

Thorax black, 0.67 mm long, wing length 2.0 mm, width 0.94 mm, lw/ww = 2.14, wing area 1.5 mm2 , TAL = 2.5, M 2/d = 1.68, M 4 ratio = 0.4, length of cell br > cell bm > cell cua, vein CuA recurved and confluent with underside of cell cua.

Hind femur pennate with scales 0.13 mm long ventrally, 0.75 mm long, 0.17 mm wide (scales not included); hind tibia approximately 0.68 mm long, 0.13 mm wide, with shorter, narrower scales ventrally; hind tarsus 0.87 mm long, 63 μm wide (T1), mid femur and tibia both narrow and without scales; all legs dark reddish in color. Abdomen brown, 1.86 mm in length, cerci 0.16 mm long.

Original research

Dale E. Greenwalt & Bradley J. Sinclair (2024). The fossil record of female sexual ornamentation in Empididae (Diptera: Empidoidea), with description of four new species. Palaeoentomology 007 (5): 611–627, DOI:10.11646/palaeoentomology.7.5.5

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