Pipunculinae, Walker, 1834

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 : 40-41

1802 Pipunculinae incertae sedis

Figure 36

Type horizon. Middle Eocene Coal Creek Member, Kishenehn Formation.

Type locality. Deep Ford site, Middle Fork of the Flathead River (Pinnacle, Montana, USA).

Differential diagnosis. This specimen is distinguished by antennal pedicel with prominent bristle and shorter setae, and a long, thin arista; body without long setae/bristles; wing with costa extending beyond apex to M 1, R 4+5 ending at the apex of the wing, M 2 present, CuA 2 merges with A 1 just before margin.

Description. Ventral aspect, female. Total length 3.64 mm (actual), 4.0 mm (estimated); color black. NMNH, USNM 625934 (Figure 36.1).

Head. Large, 1.27 mm wide, 0.89 mm long. Ocellar bristles absent. Occiput, if present, obscured/ destroyed by crack. Antenna well-preserved. Scape not clearly distinguishable. Pedicel 0.13 mm wide, length 74 μm, with one prominent ventral bristle 0.12 mm long plus some smaller bristles and at least eight smaller but distinct (30–80 μm) setae on the dorsal surface. Visible portion of F1 spherical, 73 μm wide, with several thin 33 μm setae. Arista long (0.46 mm), thin, basal portion 86 μm long, 26 μm wide (Figure 36.1).

Thorax. Quadrate, both length and width 1.43 mm. Scutum and scutellum not visible as the fossil is of the ventral aspect of the insect.

Wings. Length, 4.0 mm, width, 1.33 mm (left), 1.48 mm (right) (Figure 36.2). Pterostigma present, as long as 3 rd costal section. Ratio of length of 2 nd, 3 rd and 4 th costal sections 4.5:2.2:1. R 4+5 meets margin at wing apex, C extends beyond apex to reach M 1; r-m at 0.27 of length of discal cell. M 1+2 distal of r-m curved, convex. M 2 present, 0.61 of length of last abscissa of M 1+2; M 1 curved, convex, dm-cu slightly curved, CuA merges with CuP just before margin. Spurious veins in both wings in the basal radial cell and cells r 1+2 and r 4+5. Anal lobe present.

Legs. Five legs visible including yellow fore and hind tibiae; tibiae with short black setae. Front femur wide, black.

Abdomen. Sternites 1-5 length, 0.2 mm, 0.23 mm, 0.27 mm, 0.26 mm and 0.41 mm, respectively, wider than long, sternite 3, 1.3 mm wide. Lateral abdominal setae, if present, short. Terminalia not preserved. Length of sternite 5 strongly suggests that the specimen is a female, since males have sternite 5 considerably reduced compared to sternites 2–4 due to the genitalia complex that follows S5.

Allotype. Male unknown.

Syncompressions. None.

Remarks

Pipunculidae contains approximately 1,428 species in 22 extant genera placed in four subfamilies: Chalarinae Aczél, 1939a , Nephrocerinae Aczél, 1939b , Pipunculinae Walker, 1834 , and Protonephrocerinae Aczél, 1948 . According to molecular dating, the diversification of this family began approximately 85 Mya ( Wiegmann et al., 2011). The oldest, albeit undescribed, fossil is from the Fur Formation (about 55 Mya; Bonde et al., 2008). Members of the crown group of the family (with M 2 absent), however, existed as early as 51 Mya ( Archibald et al., 2014a). To date, 16 fossil specimens have been described ( Archibald et al. 2014a; Kehlmaier et al., 2014; this study).

The crack in this fossil has destroyed any remnant of an occiput. The first flagellomere is very small (smaller than the pedicel, which is not the case in any extant species), which raises the possibility that only the uppermost portion of this structure is visible. Except for the pedicel, no other long setae or bristles are visible on the head, thorax, legs or abdomen. This feature, in combination with the wing venation, eliminates the possibility that this species belongs to the Chalarinae , Protonephrocerinae (eliminated based on R 4+5 ending at the apex of the wing), part of Nephrocerinae ( Nephrocerus Zetterstedt, 1838 ) and part of Pipunculinae . Priabona Archibald et al., 2014 (Nephrocerinae) is not well enough known. In extant Pipunculinae , long and numerous (>5) bristles on pedicel occur especially in Claraeola Aczél, 1940 ( Eudorylini Rafael and De Meyer, 1992 ) of which many extant species also have M 2. Skevington and Yeates (2001) regard long bristles on the pedicel as a plesiomorphy while a larger number of bristles as an apomorphic condition. Despite the destroyed occiput, the fossil can be safely placed in the Pipunculinae . The characters required for a confident assignment to a tribe, however, let alone a genus, cannot be observed. The specimen is here assigned to Pipunculinae incertae sedis.

This Kishenehn Formation pipunculine is small relative to most fossils of the family. Pipunculidae species A ( Archibald et al., 2014a), Metanephrocerus belgardeae Archibald, Kehlmaier and Mathewes, 2014 , Protoverallia succinea Meunier, 1903, Nephrocerus oligocenicus, Carpenter and Hull, 1939 , Metanephrocerus collini Carpenter and Hull, 1939 , M. hoffeinsorum Kehlmaier and Skevington in Kehlmaier, Dierick and Skevington, 2014 , and M. groehni Kehlmaier and Skevington in Kehlmaier, Dierick and Skevington, 2014 , have wing lengths of 5.9, 9.2, 6, 8, 6, 6.7 and 6 mm, respectively. The body length of Eudorylas Aczél, 1940 species A is only 2.2 mm, while Eudorylas species A and B ( De Meyer, 1995) and Pipunculinae species A ( Archibald et al., 2014a) lack vein M 2. Unlike this incertae sedis Pipunculinae , both Protoverallia succinea and Metanephrocerus collini have long abdominal bristles; Metanephrocerus collini also has M 2 at the wing margin; Cephalosphaera baltica , according to Carpenter and Hull, 1939, has “smoky wings”, but this feature was not mentioned by Aczél (1948). Cephalosphaera baltica is larger than the Kishenehn Formation specimen as its wings are 5.5 mm in length ( Aczél, 1948). Pipunculidae species A, Metanephrocerus hoffeinsorium and M. groehni differ markedly from this Pipunculinae incertae sedis in the ratios of the 2 nd, 3 rd and 4 th costal sections length. Carpenter and Hull (1939) briefly reviewed Meunier’s (1903) fossils and indicated that Verrallia exstincta Meunier, 1903 , was conspecific with what Meunier termed a “variety” of V. exstincta which he referred to as V. kerteszia Meunier, 1903 . Aczél (1948) however, stated that “according to the figure, the 3 rd and 4 th costal sections are shorter than the 5 th (in V. kerteszia ), while the 3 rd and 4 th costal sections of V. exstincta are much longer than the 5 th.” In any case, both of these fossil specimens of Verrallia are twice the length of the Kishenehn specimen.

Figures

FIGURE 36. Pipunculidae sp. USNM 625934. 1, Habitus. Inset: antennae; 2, Left wing. Arrowheads denote spurious veins; Scale bars equal 2.0 mm (1), 0.25 mm (inset) and 1.0 mm (2).