Eosciarites hermes Greenwalt, 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 : 20-22

Eosciarites hermes Greenwalt , sp. nov.

Figures 16 , 17 zoobank.org/ C0541528-F65E-4593-9B09-9C1CB318C6C2 Etymology. The generic epithet is a combination of the greek word Eos (early, dawn), the genus name Sciara and the suffix “-ites” (Latin for ”having the nature of”). Eosciarites is a collective parataxon as defined by Rasnitsyn (1986; 1996). The specific epithet is the Greek word Hermes (mythical messenger of the gods).

Holotype. USNM 624633 , 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. Dakin site, Middle Fork of the Flathead River (Pinnacle, Montana, USA).

Differential Diagnosis. The absence of macrotrichia on veins M and Cu and flagellomeres with cylindrical nodes or necks differentiates this specimen from Sciara . A three-segmented palpus, R 1 joining C prior to medial fork and significantly longer than half the length of R, M+CuA significantly greater than bm-m, middle and hind tibia with a single apical tibial spur are all diagnostic of this specimen.

Description

Female (Figure 16.1). Total length 2.2 mm, light brown in colour.

Head. Black, spherical, 0.27 mm diameter; eye about 0.12 mm in diameter. Maxillary palpus threesegmented, about 0.19 mm in length, terminal two segments slightly longer than wide. Antennal base situated in a distinct depression, flagellomeres brown, quadrate basally. Apical flagellomeres not preserved (Figure 17.1).

Thorax. Black to dark red, legs light brown. Scutum covered with short scattered setae. Mediotergite with several bristles on its posterior margin, katepisternum not attentuated. Haltere light brown, knob about 0.09 mm wide and 0.16mm long.

Legs. Setose, light brown basally, tibia and tarsi darker. Forecoxa with long setae along ventral margin, hind tibia with line of spines posteriorly; middle and hind tibia with one and possibly two apical spurs respectively, spurs longer than tibia diameter; foretibia with a spur longer than foretibial diameter on either side of a dark triangular area of setae (Figure 17.2).

Wings. Length: 1.45 mm, width: 0.52 mm (Figure 16.2-3). Membrane with microtrichia, macrotrichia restricted to C, R 1 and R 4+5. C extending beyond apex of R 4+5, about half way to M 1. Sc short, free, R 1 significantly longer than half of R, R 1 with a short, brief posterior turn basally, ending well-short of medial fork. R 4+5 reaching C well before wing tip. Rs oblique to R 4+5. Base of M and stem of M 4 both shorter than r-m cross vein, ratio of r-m to M-petiole 1:2.6. M 1+2 inconspicuous, slightly longer than medial fork, M 1 and M 2 slightly divergent; cubital fork very long, with origin basal to origin of M 1+2. CuP inconspicuous or not preserved.

Abdomen and genitalia. Female, length 1.58 mm, brown; basal tergites wider than long. Tergites 3–5 with short setae at posterior margin; cercus twosegmented (Figure 17.3).

Allotype. Male unknown.

Syncompressions. Thysanoptera (1), Diptera (1).

Remarks

The family has 92 genera and 2,455 species, with a very complex taxonomy. Sciara Meigen, 1803 , with approximately 700 extant species, is one of the most species-rich genera in the class Insecta — although many of these species may be misplaced. Sciara is the largest genus in the family Sciaridae and constitutes nearly 30% of the family’s extant species. Sciara has obviously served as a default assignment for poorly preserved fossils; 89 of all 168 fossil Sciaridae are assigned to the genus ( PBDB, 2018). Species epithets such as rottensis, defectuosa, deperdita, diabolica, difficilis, ignorata, etc. may reflect authors’ frustrations in the identification of their fossil specimens ( Heyden, 1870; Scudder, 1878; Meunier, 1904b). The presence or absence of macrotrichia on veins M and/or Cu is an essential morphological character in the identification of Sciara . A common question with fossil specimens is whether the macrothrichia were ever present or whether they were just not preserved. The near universal presence of these structures on the costal and radial veins however, should serve as an internal control. Neither macrotrichia nor their sockets are preserved in veins C, R 1 and R 4+ 5 in the three species re-examined below.

While this new specimen does not appear to belong to the genus Sciara , due to the absence of macrotrichia on veins M, the fact that it is a female and the inability to determine morphological characters such as the absence or presence of a neck on the flagellomeres (Figure 17.1), make it difficult to assign the specimen to an extant genus. For an impression fossil, preservation of this specimen is exceptional, but although the claws do not appear to have teeth and the labial palps do not appear to have setae, their absence can not be definitively established. Dolichociara and Angustosciara can be eliminated due to the absence of macrotrichia on the M veins; Sciarotrichia can be eliminated due to the length of the terminal segments of its labial palps; Edidapus and Pnyxia can be eliminated as they lack a patch of anteroapical setae on their foretibia and the presence of an attenuated katepisternum; Scatopsciara can be eliminated due to R 1 less than half the length of R, Euricrium can be eliminated as it has an M fork bell-shaped, wider basally than distally; Bradysia is eliminated as its foretibia have two apical spurs; Rhynchomegalosphys and Scythropochroa can be eliminated as M+CuA is much longer than bm-m; Ceratiosciara is eliminated as it has strongly shortened convex flagellomeres; Eugnoriste is eliminated due to its greatly elongated mouthparts; Cratyna and Archicratyna are eliminated due to the presence of two midtibial spurs; Hyperlasion and Cosmosciara are eliminated due to the presence of an attenuated katepisternum (Menzel and Smith, 2017). This does not mean that the specimen does

not belong to an extant genus. However, until additional specimens are collected that may assist in such an assignment, the generic epithet Eosciarites is provided.

Figures

FIGURE 16. Eosciarites hermes sp. nov., USNM 624633. 1, Habitus; 2, Right wing, arrow points to the halter; 3, Line drawing of the right wing. Scale bars equal 1.0 mm (1) and 0.5 mm (2).

FIGURE 17. Eosciarites hermes sp. nov., USNM 624633. 1, Head, arrow points to the labellum; 2, Tibial spur of foreleg (left arrow) and tibial spur of midleg (right arrow). Arrowheads denote a small dark patch of setae; 3, Terminalia, female. Arrow and arrow head denote the two-segmented cercus and sternite 10, respectively; Scale bars equal 0.3 mm (1) and 0.5 mm (2, 3).