Microphorella fragilis Cumming and Greenwalt, 2022

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 : 33-35

Microphorella fragilis Cumming and Greenwalt sp. n.

Figures 18-19

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Type species. Microphorus praecox Loew, 1864a (original designation)

Holotype. Male, USNM 624117 , deposited in the Department of Paleobiology , National Museum of Natural History ( NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Locality and horizon. Dakin site, Middle Fork of the Flathead River (Pinnacle, Montana, USA). Middle Eocene Coal Creek Member, Kishenehn Formation.

Etymology. The specific epithet is derived from the Latin fragilis (= fragile) referring to the delicate nature of the preservation of this fossil in thin oil shale.

Diagnosis. This species of Microphorella is the first described fossil in the genus. Within the

Parathalassiinae , Microphorella is primarily characterized by a reduced anal area of the wing and complete wing venation with cell dm closed and vein M 2 present, plus the lack of features (i.e., well-developed gena, greatly lengthened antennal stylus, enlarged palpus and double row of costal spine-like setae) that characterize other parathalassiine genera with this type of wing ( Cumming and Brooks, 2019). Within this broad definition of the genus, Microphorella fragilis can be separated from other species of Microphorella by the combi-

GREENWALT ET AL.: KISHENEHN FORMATION DIPTERA nation of a broad wing with a short R 1 vein and an abruptly tapered postpedicel apically.

Description (male). ( Figure 18A ). Head, thorax and genitalia black, abdomen and legs dark brown, body length 1.75 mm. Head 0.28 mm long, 0.37 mm high, subquadrate (possibly deformed) with large ocellar triangle; ocellar setae 67 μm in length; dichoptic, ommatrichia on eyes not discernible, frons and face broad; gena narrow. Antenna inserted just above middle of head, reddish brown (left antenna detached and inverted towards head), scape and pedicel not visible, flagellum 0.29 mm long, postpedicel 0.11 mm long, abruptly tapered apically, basal portion of postpedicel spherical, 55 μm in length, stylus with single article, 0.18 mm in length (1.6 times length of postpedicel). Palpus narrowly ovoid ( Figure 19A , arrow), about 90 μm long, 30 μm wide, setose apically; proboscis short, projecting ventrally. Thorax 0.70 mm long, strong postpronotal seta apparently absent, various scutal setae and a single pair of long apical scutellar setae, 0.20 mm in length present ( Figure 19B ). Wing ( Figure 18 B-C) broad with anal lobe not developed, 1.24 mm long, 0.61 mm wide, covered with minute microtrichia, pterostigma absent. Costa circumambient, weaker posteriorly, with single row of short evenly spaced setae anteriorly; Sc faint apically; R 1 short, reaching costa just before mid-length of wing (or before level of base of M 2); base of Rs originating opposite humeral crossvein; R 2+3 diverging from R 4+5 apically; M 1 diverging from R 4+5 beyond cell dm; M 1 and M 2 strongly diverging beyond cell dm; M 2 and M 4 nearly parallel beyond cell dm; short crossvein r-m present; crossvein bm-m nearly complete basally; cell dm present and closed; cell cua closed, rounded apically with CuA recurved; CuA+CuP slightly extended beyond cell cua. Femur, tibia and tarsus of hind and mid-legs 0.40, 0.35, 0.33 mm and 0.30, 0.40 and 0.31 mm long, respectively. Hind trochanter without spine bearing tubercle; hind femur with several widely-spaced, long thin setae, 70 μm in length; hind tarsus with tarsomere 1 as long as combined length of tarsomeres 2–5. Abdomen slightly longer than thorax, stout, 1.0 mm long including terminalia. Terminalia large and globular, about half length of abdomen, asymmetrical, lateroflexed to right and inverted with posterior end directed anteriorly; in right lateral view with large hypandrium dorsally and probable right cercus posteroventrally ( Figure 19C , arrow) with additional lobes anteroventrally.

Female. Unknown.

Synimpressions. Dipteran pupae (5), Chironomidae (20), Hymenoptera (1), Chalcidoid (1), Diptera (1) and Notonectidae (1)

Remarks. The subfamily Parathalassiinae , along with the Microphorinae , is one of the basal subfamilies in the Dolichopodidae s.lat. ( Sinclair and Cumming, 2006). Worldwide, the Parathalassiinae currently includes 51 described extant species in eight genera and approximately 45 additional undescribed species ( Cumming and Brooks, 2019). The described genera are as follows: Amphithalassius Ulrich, 1991 , Chimerothalassius Shamshev and Grootaert, 2002 , Eothalassius Shamshev and Grootaert, 2005 , Microphorella Becker, 1909 , Neothalassius Brooks and Cumming, 2016 , Parathalassius Mik, 1891 , Plesiothalassius Ulrich, 1991 and Thalassophorus Saigusa, 1986 . In addition, there are three fossil genera ( Cumming and Brooks, 2019), namely Archichrysotus Negrobov, 1978 , Cretomicrophorus Negrobov, 1978 and Retinitus Negrobov, 1978 , from various Late Cretaceous ambers ( Grimaldi and Cumming, 1999), and Electrophorella Cumming and Brooks, 2002 from Baltic amber.

As presently classified, Microphorella differs from the taxa listed above primarily by wing venation and wing shape. The genus possesses wing cell dm, which is closed by the base of M 2 and crossvein dm-m and emits three veins, M 1, M 2 and M 4. Cell cua is apically rounded with vein CuA recurved, and the shape of the wing is characterized by a reduced anal area ( Cumming and Brooks, 2019). In addition, Microphorella has a narrow gena, antennal stylus that is not greatly lengthened, short palpus, single pair of apical scutellar setae and single row of costal spine-like setae, which are features that also separate it from other parathalassiine genera.

Microphorella fragilis is the first fossil of the genus Microphorella and the first Nearctic parathalassiine fossil from the Cenozoic. It can be distinguished from other species of the genus by the combination of a broad wing with short R 1 vein and an abruptly tapered postpedicel apically. The affinities of M. fragilis within Microphorella are probably with the short R 1 group as defined by Cumming and Brooks (2019), a species group currently known only from western North America and one that may eventually need elevation to generic level.

Figures

FIGURE 18. Microphorella fragilis Cumming and Greenwalt sp. n., USNM 624117, male. A, Habitus; B, Right wing; C, Wing drawing. Scale bars equal 1.0 mm (A) and 0.5 mm (B).

FIGURE 19. Microphorella fragilis Cumming and Greenwalt sp. n., USNM 624117, male. A, Head; arrow points to pal- pus; B, Scutum; C, Male terminalia; arrow denotes cercus. Scale bars equal 0.2 mm (A, C) and 0.5 mm (B).