Macrocera apithanos Kerr 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 : 17-21

Macrocera apithanos Kerr and Greenwalt sp. n.

Figures 8-11

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Type species. Macrocera lutea Meigen, 1804 , by subsequent designation ( Guérin, 1826).

Holotype. Male, USNM 624407 , deposited in the Department of Paleobiology , National Museum of Natural History ( NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Type locality and horizon. Dakin site, Middle Fork of the Flathead River (Pinnacle, Montana, USA).

GREENWALT ET AL.: KISHENEHN FORMATION DIPTERA

Middle Eocene Coal Creek Member, Kishenehn Formation.

Etymology. The specific epithet is a Greek term that means unlikely, improbable, and refers to the rarity of fossils that preserve very long, thin antennae.

Diagnosis. This species of Macrocera is distinguished from other fossils of the genus by its very long antennae, wing length/body length ratio and short vein Sc.

Description (male). ( Figures 8-9 , 11B ). Body length 3.3 mm. Head dark brown, much wider than long, 0.61 mm x 0.23 mm. Antenna (left) 8.8 mm long, narrow, 2.7 times body length; F1 66 μm wide at base, terminal flagellomere half that width at tip, basal flagellomeres ≥ 6 x pedicel length. Thorax yellowish, 0.54 mm wide, length difficult to determine due to poor preservation of relatively long, wide and less pigmented pronotum. Scutum pillose, uniformly covered by long (0.15 mm) dark brown setae; subcoxal pleural sclerites prominent, black ( Figures 8A , 9C ). Wing 3.9 mm long, 1.4 mm wide, with microtrichia. Sc terminates in C at level slightly distal of m-cu origin; costa extending 0.2 distance from R 5 to M 1. R 2+3 angled about 10° from horizontal, origin in line with terminus of R 1; Rs+M fusion minimal, present as heavily sclerotized junction only; base of M 4 with very slight curve; m-cu acutely angled (about 45°). Distal quarter of wing along anterior, apical and posterior margins of the wing infuscate ( Figure 9 A-B, 11B). Legs light brown, setose; fore, mid and hind femora 0.86, 1.62 and 1.62 mm long, respectively; fore, mid and hind tibiae 1.37, 2.42 and 1.87 mm long, respectively; fore, mid and hind tarsi 1.71, 2.02 and 2.19 mm long, respectively; apical ¾ of fore tibia with single row of short stout anteroventral spines; abdomen 1.87 mm long (genitalia not included), uniformly wide at approximately 0.4 mm, entire length of abdomen pilose, covered with uniformly long (0.15 mm) setae. Genitalia dark brown/black, gonostylus curved, hook-like, about 0.32 mm long, terminal quarter black, highly sclerotized ( Figure 8B ).

Synimpressions. Aphididae (5), Mymaridae (1), Chironomidae (1), Hemiptera (1), Thysanoptera (3)

Figures 10 A-D, 11C

Allotype. Female, USNM 729602 . Allotype and paratype USNM 768010 deposited in the Department of Paleobiology , National Museum of Natural History ( NMNH) , Smithsonian Institution, Washington, District of Columbia, USA .

Type locality and horizon. Park site (allotype), Dakin site (paratype), Middle Fork of the Flathead River ( Pinnacle , Montana, USA). Middle Eocene Coal Creek Member , Kishenehn Formation .

Description. Allotype female ( Figure 10A ) body length 4.2 mm. Head dark brown, wider than long, 0.55 mm x 0.36 mm; cerebral sclerite apparently present, roughly square in shape, approximately 0.18 mm /side. Antenna (left) setose, 3.9 mm long, narrow, terminal flagellomeres missing. Pedicel about 75 µm in diameter, uniformly setose; F1 60 µm wide at base, 0.52 mm long ( Figure 10 A-B). Thorax yellowish, 0.57 mm wide, 1.1 mm long, alar setae plentiful, dorsocentral setae less so. Subcoxal pleural sclerites present, black. Wing 3.6 mm long, 1.4 mm wide, with microtrichia. Sc terminates in C at level slightly distal of m-cu origin; costa extending 1/3 distance from R 5 to M 1. R 2+3 origin in line with terminus of R 1; Rs+M fusion not visible, base of M 4 with distinct curve towards CuA (as in paratype, Figure 11D ), more pronounced than that in holotype male; m-cu not acutely angled (parallel to costa in paratype). Entire distal half of wing infuscate ( Figures 10A , 11C ). Legs light brown, uniformly setose, mid and hind femora 1.2 and 1.4 mm long, respectively; fore, mid and hind tibiae 1.1, 1.7 and 2.0 mm long, respectively; fore, mid and hind tarsi 1.25, 1.9 and 2.1 mm long, respectively; hind tibia with two prominent spurs ( Figure 10C ). Abdomen 2.5 mm long (genitalia not included), maximum width approximately 0.7 mm, entire length of abdomen pilose, individual segments well defined. Genitalia light brown, two black spermathecae present, cerci about 40 mm in diameter and extend about 0.14 beyond sternite 8 ( Figure 10D ).

Synimpressions. Aphididae (1)

Remarks. The family Keroplatidae (superfamily Sciaroidea ) consists of 130 genera and about 1,000 species, 67 of which are fossils distributed among 29 genera ( Evenhuis and Pape, 2021). The family’s most speciose genus, Macrocera , has about 200 extant species and a worldwide distribution ( Evenhuis, 2006; Sasakawa, 2zhe antennae are “protruded, filiform, long and ... cylindrical”. Although the antenna of the holotype for the genus, M. lutea (designated by Guérin [1826]), was described by Meigen (1804) as “long or longer than the insect”, the antennae of this genus may or may not be longer than the body and in some species, they are relatively short (reviewed in Vockeroth, 1981; Blagoderov and Ševčík, 2017).

The holotype of Macrocera apithanos has an intact antennae 2.7 times as long as the body of the fly as well as vein M 4 slightly curved towards CuA at its base ( Figures 8A , 9 A-B, 11B). Although the thorax and abdomen are poorly preserved, with individual segments of the abdomen indiscernible, specimen USNM 624407 is designated as the holotype as it is a male and its genitalia are preserved, albeit poorly. The allotype ( Figures 10 A-D, 11C) and its paratype ( Figure 11A,D ) are better preserved although, in each case, the antennae appear to be incomplete. The wings of both the allotype and paratype females differ from the male in the greater extent of infuscation. The base of vein M 4 in the females is better preserved and curved to a greater degree towards CuA than in the male ( Figure 11 B-D).

A large number of Cretaceous species of Sciaroidea have been described, including Burmacrocera petiolata Cockerell, 1917 (sex undetermined) from Myanmar ( Blagoderov and Grimaldi, 2004). Burmacrocera petiolata is a small species with a wing length of 2 mm and an antennal length of 1.2 mm. The venation of B. petiolata is similar to M. apithanos but the Eocene species a shorter Sc, R 1 and R 2+3 less steeply angled to C, M 1+2 shorter, M 1 reaching margin below wing apex, M 4 bent towards the posterior and CuA reaching the wing margin. The older literature contains a number of species designated as Macrocera that were subsequently reassigned: Meunier (1899) listed, but neither appropriately described nor figured, M. grandis Lundström, 1912 and M. minuta Meunier, 1899 from Baltic amber and both have been declared nomina nuda by Evenhuis (2006). Macrocera abundare Meunier, 1904 , M. ciliata Meunier, 1904 and M. filiformis Meunier, 1904 were described and figured by Meunier (1904) but were subsequently assigned to the extinct genus Kelneria Matile, 1979 which differs from Macrocera in that R 1 is shorter (less than half the length of the wing) and its basal cell is reduced. Six fossil species of the genus, all from the Cenozoic, are currently known. Macrocera electracornis Evenhuis, 2006 [ M. longicornis Meunier, 1904 ], a male from Baltic amber, was figured with an antenna three times body length but with Sc long (0.64 x wing length vs. 0.38 x wing length for M. apithanos ). Macrocera soccata Meunier, 1899 (male) and M. elegantissima Meunier, 1904 (female), both from Baltic amber, have antennae about half the body length, and antennae reaching the end of the abdomen, respectively. The genitalia of Macrocera soccata are figured as long and thin; M. elegantissima has flagellomeres <4 x the length of the pedicel, vs. ≥ 6 x in M. apithanos . The antenna of Macrocera melanopoda Hong, 1974 (male) from 50 Ma amber of the Guchengzi Formation in the Liaoning Provence of China, is relatively short, about 1.3 mm in length ( Hong et al., 1974). Additionally, the curvature of the gonostylus of Macrocera melanopoda is much less than that of M. apithanos (about 90° vs. 180°, respectively).

Two fossil species are preserved as compression fossils, M. archaica Armbruster, 1938 ( Armbruster, 1938), sex unknown, from the Miocene Randeck Maar and M. umbonata Statz, 1944 ( Statz, 1944), a female from the Oligocene Rott Formations of Germany. Neither described the antennae – the antennae are missing in M. umbonata . The former species, as originally figured, has the M fork – which Armbruster referred to as “Archaic” – at the level of the terminus of R 1, while in M. apithanos , R 1 ends far distad of the fork. In addition, R 2+3 originates far distal to the terminus of R 1 and is closer to vertical than horizontal (50°) in M. archaica while, in M. apithanos , this vein is closer to horizontal (10°) and originates below the terminus of R 1. Both M. umbonata and M. archaica are larger than M. apithanos (4.7 mm and 5.5 mm, respectively, vs. 3.3 mm) but more importantly, the ratio of wing length to body length in these two species is less than one (0.91 and 0.76, respectively) vs. 1.18 in M. apithanos . Both M. archaica and M. umbonata have the fusion of Rs and M (Rs+M) equal to or longer than the basal sector of M 1+2, whereas in M. apithanos , the junction of Rs and M 1+2 is no more than a thickening of the veins at that point. Macrocera umbonata also differs from the North American fossil in that m-cu in the former is horizontal while it is acutely angled at about 45° in M. apithanos . The genitalia of Macrocera umbonata were neither described nor figured.

Figures

FIGURE 8. Macrocera apithanos Kerr and Greenwalt sp. n., USNM 624407, male. A, Habitus; B, Genitalia. Black arrows denote setae; white arrow denotes a row of fore tibial spines. Scale bar equals 5.0 mm (A) and 0.5 mm (B).

FIGURE 9. Macrocera apithanos Kerr and Greenwalt sp. n., USNM 624407. A, Left wing; B, Left wing, drawing; C, Body, setose. Scale bars equal 1.0 mm.

FIGURE 10. Macrocera apithanos Kerr and Greenwalt sp. n. (allotype), USNM 729602, female. A, Habitus. B, Head, dorsal view. Arrows from top to bottom denote end of F1, spherical setose pedicel and cerebral sclerite. C, Hind tibial spurs. D, Genitalia. Scale bars equal 5.0 mm (A), 0.5 mm (B), 0.2 mm (C), and 0.5 mm (D).

FIGURE 11. Macrocera apithanos Kerr and Greenwalt sp. n. A, Habitus of paratype female, USNM 768010. B-D, Area of wing basal of vein M1+2 of B) holotype, C) allotype female and D) paratype female. Scale bar equals 3.0 mm (A).