Bibionidae, , Hardy, 1945

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 : 13-14

Bibionidae incertae sedis stat. rev. ( Dilophus magnus Dürrenfeldt, 1968 )

Figure 5

Holotype. GZG.W.14836 (originally 612-6 [ Dürrenfeldt, 1968]), both part and counterpart, is housed at the Geowissenschaftliches Museum in Göttingen , Germany.

Redescription. Sex unknown. ventral view (abdomen and part of thorax) and dorsal view (part of thorax) body length approximately 2 cm. Details of head and antennae not preserved ( Figure 5 A-C). Dorsal portion of thorax, with left wing attached, partially preserved. Mesonotum, probably light brown and concolorous with ventral part of thorax, with distinct convergent mesonotal furrows; mesonotal spines absent. Wings, overlapped and flipped horizontally relative to one another, preserved on right side of body, at least 1.65 cm long, 6.7 mm wide; Costa apparently terminates at R 4+5; Sc long, reaching C at level distal to the distal end of r-m; pterostigma slightly oval, not touching R 4+5; bRs veins 0.92 and 0.81 mm in length, r-m veins 0.96 and 0.96 mm in length; M 1 +M 2 and portions of M 1 present, M 2 and M 4 not visible; CuA very prominent, CuP not preserved ( Figure 5 ). Hind femur, tibia and tarsus 4.1, 5 and 4.6 mm long respectively; abdomen 1.2.cm long, 5 mm wide details of genitalia not preserved.

Remarks. Dilophus magnus was collected from the Willershausen clay pit, a Piacenzian (2.6 – 3.6 Ma) pond marl in Germany and described by Dürrenfeldt (1968). The description consisted mostly of body coloration with some limited data on wing venation. As originally described, the specimen is unusual relative to Dilophus in a number of respects (e.g., a relatively short r-m and a relatively long distance between the origin of Rs and the terminus of Sc). Dürrenfeldt stated that, despite the absence of the fore legs and their diagnostic tibial spines, the specimen could be identified to the genus Dilophus based on C terminating beyond R 4+5. Based on study of the holotype we disagree with Dürrenfeldt’s interpretation and believe C terminates at R 4+5. However, regardless of the interpretation of the termination point of C, we argue here that this character alone is insufficient for such an identification. The Neotropical genus Bibionellus Edwards, 1935 (e.g., B. barrettoi Lane and Forattini, 1948 ) and some African species of Bibio (e.g., B. turneri Edwards, 1925 ) have the costa extending beyond the last radial vein ( Hardy, 1950; Pinto and Amorim, 1997). In addition, the length of r-m in Dilophus is often quite a bit longer (often 2-3 times as long) than the base of Rs, which is not the case in D. magnus where r-m and base of Rs are almost subequal (it should be noted that Skartveit and Nel (2017) reassigned D. luteipennis , from Bibio , although its wing has r-m/bRs nearly subequal [their figure 213]). However, this species has neither C extending beyond R 4+5 nor evidence of fore tibial spines. Lastly, there is no indication of mesonotal spines on the piece of the mesonotum associated with the left wing. We treat D. magnus as Bibionidae incertae sedis.

Figures

FIGURE 5. Dilophus magnus Dürrenfeldt, 1968, GZG.W 14836. A, Habitus (part); B, Wing (part), arrows denote r-m crossvein of two overlapping wings; C, Habitus (counterpart); D, Wing (counterpart); E, Apex of wing (counterpart), arrow denotes vein R4+5; F, Drawing of wing. Scale bars equal 1.0 mm (A,C), 0.5 mm (B,D), and 0.2 mm (F).