Bibiodes kishenehnensis Fitzgerald, 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 : 19-20

Bibiodes kishenehnensis Fitzgerald , sp. nov.

Figures 14 , 15

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Etymology. The specific epithet is named after the Kishenehn Formation in which the holotype was preserved.

Holotype. USNM 625738 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. Spring site, Middle Fork of the Flathead River (Pinnacle, Montana, USA).

Differential diagnosis. Bibiodes kishenehnensis is a typical representative of the bibionid genus Bibiodes that is distinguished from other genera by the elongated coalescence of the stem of M and Rs veins. B. kishenehnensis is distinguished from fossil congeners by the following combination of characters: coalescence of stem of M and Rs longer (coalescence 0.43 mm and slightly longer than base of Rs), wings brown fumose (especially at anterior apical portion of wing), stigma strongly pigmented, legs black and hind basitarsus about four times as long as wide (width measured at midpoint).

Description

Female (Figure 14.1), body length (excluding antennae) 6.8 mm.

Head. Black, antennae and palps black, number of flagellomeres not discernible, as base of antennae are hidden (Figure 15.1).

Thorax. Ventral and visible lateral portions black, dorsum hidden from view.

Wings. 5.2 mm long (base of wing estimated for measurement) by 1.8 mm wide (measured at level of apical end of coalescence of stem of M and Rs (Figure 14.2-3). Anterior veins except Sc (C, radial veins, base of M including junction with Rs) bold, strongly pigmented dark brown. Sc and apical tips of medial veins faint, light brown, remainder of veins unpigmented. Sc long, fading out before stigma (presumably not reaching C as in extant species). Pterostigma strongly pigmented, dark brownish black, elongate. Wing membrane distinctly brown fumose along anterior margin from stigma to just beyond apical end of C and slightly light brown fumose elsewhere, but especially along wing edge to about M 4. Costa continued only slightly as tiny stump beyond junction with R 4+5.

Legs. Black. Length of spur of anterior tibia not discernible. Hind femur about 1.4 mm long (base of femur estimated), swollen, 0.44 mm wide (width measured at widest area on apical third). Hind tibia not swollen, straight-sided, but gradually thickened distally, 1.5–1.6 mm long by 0.28–0.30 mm wide (width measured at apex; Figure 15.3). Hind basitarsus slender, gradually slightly more robust distally, about four times as long as wide, 0.48-0.60 mm long by 0.16 wide (width measured at midpoint of basitarsus).

Abdomen and genitalia. Abdomen brown, broad, as is typical for females. Cerci light brown, ovate, with fine setae, projecting posteriorly (Figure 15.2).

Allotype. Male unknown.

Syncompressions. None.

Remarks

The family Bibionidae sensu stricto (excluding Hesperinus Walker, 1848 , but including both fossil and extant forms) consists of nine genera ( Fitzgerald, 2004; Skartveit, 2008) and 1,102 species ( Pape et al., 2011), and is distributed worldwide. Roughly 328 of these are fossil species ( PBDB, 2018), an unusually large number given the relatively small number of extant species, which is perhaps an indication of the clade being more diverse or at least more abundant in the past. However, Skartveit and Nel (2017) recently synonymized the fossil Bibio conformans Théobald, 1937 , with B. celasensis Theobald, 1937 , and suggested that B. obtusus Théobald, 1937 , and B. tenuiapacalis Théobald, 1937 , may also be synonyms. The validity of many other fossils is uncertain. Most (70%) of the fossil species date from the Miocene and Oligocene, with 79 species from the Eocene epoch.

The genus Bibiodes contains four extant species. Five fossil species, B. balticus Skartveit 2008 , B. intermedia James, 1937 , B. confluens Cockerell 1915 , B. provincialis Skartveit and Nel, 2017 , and B. nanus Skartveit, 2008 , have been described from the Eocene and Oligocene ( Cockerell, 1915; James, 1937; Skartveit, 2008; Skartveit and Nel, 2017). Bibiodes kishenehnensis differs from most fossil congeners in part by the longer coalescence of the stem of M with the base of Rs ( Figure 14 ; see additional characters in diagnosis) and in this regard is more similar to extant western Nearctic species of Bibiodes .

The Kishenehn Formation fossil insect collection contains 162 specimens of Bibionidae , including additional specimens of Bibiodes and several putative new species. The holotypes of Plecia akerionana Fitzgerald, 1999 , and Bibiodes (= Bibiodites ) confluens are housed at the NMNH.

Figures

FIGURE 14. Bibiodes kishenehnensis sp. nov., USNM 625738. 1, Habitus (ventral aspect); 2, Right wing showing the fusion of Rs and M; 3, Line drawing of the right wing. Scale bars equal 3.0 mm (1) and 1.0 mm (2).

FIGURE 15. Bibiodes kishenehnensis sp. nov., USNM 625738. 1, Head. Arrowhead points to the antenna; arrow points to the terminal palpomere; 2, Genitalia; 3, Left metatibia and tarsi. Arrow points to the tibial spur. Scale bars equal 0.5 mm (1, 2, 3).