Dilophus krantzii L. Heyden, 1870

Skartveit, John & Wedmann, Sonja, 2021, A Revision of fossil Bibionidae (Insecta: Diptera) from the Oligocene of Germany, Zootaxa 4909 (1), pp. 1-77 : 54-55

Dilophus krantzii L. Heyden, 1870

Dilophus Krantzii L. Heyden 1870: 255–257 .

Localities: Rott

Type (male): Coll. Krantz, Bonn (not seen)

Additional specimen (female, tentatively associated) Siegburg SU RO Kolz A 0082, counterpart SU RO Kolz A 0085.

Description:

Female (N=1, tentatively associated):

Total length 12.0 mm, seemingly entirely blackish-brown

Head: Length 1.5 mm, oval, complex eye relatively large, not protruding. Rostrum extending slightly in front of head. Ocellar tubercle small, not very proiminent. Antenna and palpus not preserved.

Thorax: Length 3.4 mm. Pronotum distinctive as usual for genus. Thoracic spine combs difficult to see. Haltere brownish-black.

Legs: Only one fore tibia and apical part of one hind tibia reasonably well preserved. This is about 1.6 mm long and 0.27 mm wide, in basal third with at least two (maybe as many as 5) strong, erect, sharp spines, possibly with two smaller spines at about two thirds the length. Apical spine comb not preserved.

Wing: Length 9.0 mm, width 3.2 mm, length/width = 2.8. Blackish fumose. The membrane has paler and darker patches, but it is difficult to tell if this is of taphonomical origin or traces of a pattern in life. Pterostigma 1.2 mm long, 0.29 mm wide, dark brown, narrow, distinctive. The veins are light brown, robust throughout, but only partially preserved. Radial sector a little longer than crossvein R-M. Crossvein M-CuA joins M 2 slightly apicad of furcation. Vein measurements in mm: basal R 2.5, R 1 2.1, Rs 0.6, R 4+5 4.9, R-M 0.5, basal M 2.0, distal M 1.6, M 1 3.6, M 2 3.4, M-Cu 0.8, CuA 1 4.1.

Abdomen: Length 7.1 mm, cylindrical. Cerci small and slender.

Male (gleaned from L. Heyden (1870):

Body length 12.0 mm. Entirely black.

Head length approx. 2.1 mm (measured from Heyden Fig. 24). Flagellum compact with at least 8 segments. Palpus twice as long as antenna, 4-segmented. (is Heyden’s «palpus» in fact a dislocated tarsus?).

Thorax: Length approximately 4.5 mm. Haltere dark.

Legs: Strong, fore- and mid coxae as long as femora. Fore- and mid tibiae a little longer than the femora. Hind femur length 4.4 mm, hind tibia length 3.3 mm, hind first tarsomere 1.1 mm, following tarsomeres 2.2 mm. Hind leg quite slender.

Wing: Length approx. 9.5 mm, width approx. 3.0 mm. Hyaline or slightly fumose, veins distinctive? Pterostigma dark and distinctive. Basal Radial sector about twice as long as crossvein R-M. R 4+5 rather straight. Fork of M relatively short, not much longer than the stem beyond crossvein R-M. Crossvein M-Cu meets M 2 some distance apicad of furcation.

Abdomen: Length 6.5 mm. First segment said to be about twice as wide as the second, but this is not apparent from the figure. Terminalia apparently not possible to make out.

Discussion:

There seem to be some discrepancies between Heyden’s written description and his Fig. 24. Meunier (1894) discussed this specimen based on Heyden’s description, apparently without having seen the specimen himself. Meunier stated that the description gave no evidence of the species belonging to the genus Dilophus , seemingly ignoring that Heyden stated the specimen had a circlet of spines apically on the protibia. If the species indeed is a Dilophus , it should be recognizable on account of its size. The figure in the original description ( Heyden 1870: Taf. XIV, Fig. 24) suggests a reasonably well preserved, male specimen. Unfortunately, we have not been able to trace the type specimen, the Krantz collection appears to have been scattered rather widely. The female specimen is associated with D. krantzi based on its size alone. Rather few Dilophus species in the recent fauna grow as big as 12 mm, this is likely to have been the case with the fossil species as well, though fairly large Dilophus species are known from fossils ( Skartveit & Krizmanić 2020).