Efcookella nigra 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 : 16-19

Efcookella nigra Greenwalt , sp. nov.

Figure 12 zoobank.org/ B16260A9-30BA-4765-9CEA-98FFDF806172 Etymology. The specific epithet is derived from the Latin term nigra for black, the colour of the insect.

Holotype. USNM 618088 , 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. This species of Efcookella is distinguished by R 1 very short, C terminating just beyond R 4+5 significantly basal of the wing apex, the presence of a complete R 4+5 -M 1 cross vein, M 1 and M 2 diverging abruptly close to the wing margin and CuA not sigmoidal in shape. Flagellomeres compact, much wider than long.

Description

Body length 2.3 mm long, sex undetermined; entire body black (Figure 12.1).

Head. Head 0.24 mm long, 0.30 mm high; antennal flagellum, 0.28 mm long, eight flagellomeres, transverse, approximately 25 μm long and 65 μm wide.

Thorax. Scutum 0.64 mm long, tibia about 2/3 length of tarsus.

Wing. Membrane uniformly covered with microtrichia; wing length 1.99 (left), 1.81 mm (right), right wing width, 0.96 mm (Figure 12.2-3). Anterior veins C, R 1 and R 4+5 darkly pigmented; R 1 short, extending only about 1/4 the length of the wing, costa ending just distal of apex of R 4+5, well before wing apex; cross vein r-m minimal. Relatively long R 4+5 extends to 0.62 (left) and 0.65 (right) of wing length. M very lightly sclerotized, forked, M 1 and M 2 diverging abruptly before wing margin, faint R 4+5 -M 1 cross vein present, CuA strongly curved towards wing margin but not sigmoidal, CuP not visible.

Abdomen and genitalia. Abdomen 1.50 mm long, 0.4 mm in height, bulbous apically, genitalia not preserved sufficiently for characterization.

Allotype. Sex unknown.

Syncompressions. None.

Remarks

Scatopsidae is a family of very small flies, with 407 species in four subfamilies and 34 genera ( Pape et al., 2011). The genus Efcookella contains 21 extant species ( EOL, 2017). The fossil record of Scatopsidae was reviewed by Amorim (1998), subsequent to which new species have been added by Nel and Prokop (2004), Fate et al., (2013) and Nel and Coty (2016); there currently are 18 species of fossil Scatopsidae . Of the fossil species, 13 belong to extant genera although Scatopse grassaris Meunier, 1907 and S. crassicornis Meunier, 1907 are considered Scatopsidae incertae sedis. Additionally, Amorim (1998) has suggested that Procolobostema incisum Cook, 1971 , and P. obscurum Cook, 1971 may be synonyms of P. hurdi Cook, 1971 . According to Amorim (1998), most males of this genus lack the crossvein R 4+5 -M 1 while females have an incomplete R 4+5 -M 1, cross vein. Several specimens from Cretaceous amber from Myanmar, Canada, New Jersey and Lebanon have been reported but not described ( Pike, 1994; Grimaldi et al., 2000; Rasnitsyn and Ross, 2000; Poinar and Milki, 2001).

Sinoscatopse eocenica Hong, 2002 , is a potentially interesting specimen but it does not appear to be a scatopsid. As described by Hong (2002), S. eocenica has a four segmented palpus (vs. a one segmented palpus in Scatopsidae ), antennae “like the antennae of a female mosquito” with its flagellomeres longer than wide and “plumose” with a pair of setae/segment ≥ in length than the flagellomeres themselves, whereas the flagellomeres of scatopsids are compact and wider than long. In addition, S. eocenica has prominent tibial spurs on all legs (absent in Scatopsidae ). Most interesting is the wing venation: Rs originates at the mid-point of the wing with the first abscissa of M> 1/2 wing length. In all scatopsids, the cubital fork is at the very base of the wing vs. the presence of a significant stem in S. eocenica . The specimens described in Hong (2002) are stated to be housed in the Chinese Geology Museum, the Beijing Natural History Museum or personal collections; however, no single specimen has its location indicated. Until the specimen can be located and re-examined, it must be considered as Diptera incertae sedis.

Of the 18 described fossils of Scatopsidae , 17 are in amber. The exception, Reichertella fasciata Melander, 1949 , was described from the 34 myo Florissant Formation. This specimen is unique amongst the Scatopsidae in having a long R 4+5 that closely parallels the costa for most of its length. Amorim (1998) elected to preserve the original placement. Meyer (2002) lists and figures another specimen (PU-6943) of R. fasciata that was collected by the Princeton scientific expedition of 1877. This specimen, housed at the NMNH (USNM 112563), is not a type specimen. Inspection of this specimen ( Figure 13 ) does not support its assignment to the family Scatopsidae . The body is 4.5 mm in length, large for a scatopsid, with numerous bristles on the head, scutum and scutellum. This specimen is either lacking its antennae or has antennae unlike that in Scatopsidae . Most importantly, the venation is very unlike that of a scatopsid. The anterior veins are not particularly more strongly pigmented than the posterior veins. Both medial and cubital forks are present, and CuA is subparallel to M 4 and does not curve markedly towards the posterior margin, as is the case in all Scatopsidae . This specimen is assigned to Diptera indeterminate.

Efcookella nigra keys to Scatopsinae Newman, 1834 , as Aspistinae Rondani, 1840 (C swollen at junction of R 4+5), Ectaetiinae Enderlein, 1936 (stem of M 1+2 arising distal to base of R 4+5) and Psectrosciarinae Cook, 1963 (base of M 2 arising at base of R 4+5) are characterized by states not found in the fossil. Critical character states that define the tribes of Scatopsinae , Rhegmoclematini Cook, 1955 (CuA sigmoid in shape), Scatopsini Newman, 1834 (basal third of CuA gently curved towards wing margin and medial fork without a "constriction" midway to apex/R 4+5 -M 1 cross vein absent), Swammerdamellini Cook, 1972 (R 4+5 not extending beyond middle of wing — this is not the case for the genus Pararhexosa Freeman, 1990 ; this genus however has ten flagellomeres) and Colobostematini Amorim, 1994 (basal third of CuA strongly curved towards wing margin) suggest that this specimen can be assigned to Colobostematini (Amorim, 2009) . Of the six genera in Colobostematini , the specimen keys to Efcookella (formerly Cookella — see Haenni, 1998) based on CuA not sigmoidal, R 4+5 -M 1 cross vein present and scutum longer than wide. The single fossil species of Efcookella , E. eocenica Nel and Prokop, 2004 , was described from 53 Mya amber from Le Quesnoy, France. Efcookella nigra is larger than E. eocenica (2.3 mm body length vs. 1.86 mm, 124%), its wings are approximately 50% longer, its scutum is 71% longer (0.64 mm vs. 0.375 mm) and the shape of the cell formed by the cross vein R 4+5 -M 1 and the terminal abscissa of M 1 is markedly different in

shape: the terminal abscissa of M 1 in E. eocenica angles downwards from R 4+5 -M 1 at an angle of 33° while that of E. nigra is inline with the more basal abscissa of M 1.

Figures

FIGURE 12. Efcookella nigra sp. nov., USNM 618088. 1, Habitus. Inset: antennae, asterisk denotes the pedicel; 2, Left wing. Arrows mark the R5-M1 cross vein; 3, Line drawing of wing. Scale bars equal 1.0 mm (1), 0.1 mm (Inset) and 0.5 mm (2).

FIGURE 13. Reichertella fasciata (PU-6943; USNM 112563). Left wing. White arrows denote the medial and cubital forks. Inset: habitus; black arrows denote bristles. Scale bars equal 2.0 mm