Rymosia hypnolithica Kerr, 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 : 24-26

Rymosia hypnolithica Kerr , sp. nov.

Figures 21 , 22 zoobank.org/ 8C1B7B7A-C82A-400D-AC71-CA596FF9DC50 Etymology. The specific epithet is a combination of the Greek terms hypnos (sleep) and litho (stone), meaning asleep in stone.

Holotype male. USNM 624134 , 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 Rymosia is differentiated from all other fossils of the genus by the combination of its small size; cubital fork basal of r-m terminus; wings hyaline, without color; and heavily sclerotized gonostylus with dorsoapical process.

Description

Body length 3.50 mm (4.05 mm including genitalia), male, head and scutum black, abdomen light brown to brown, darkening distally (Figure 21.1).

Head. Ovoid, 0.5 mm high, 0.40 mm wide, vertex and face setose. Antenna with 14 flagellomeres, flagellomere two poorly defined, terminal flagellomere longer than wide, 0.40 mm wide, 0.10 mm long. Pedicel poorly defined, with two longer setae dorsally, approx. 0.60 mm and 0.10 mm in length, respectively (Figure 21.1).

Thorax. Length 0.90 mm. Scutal setae on dorsal surface, proepisternal bristles present, but other pleura not distinguishable, a single pair of very long (0.44 mm) bristles at posterior end of scutellum.

Wings. Left wing, 2.75 mm long, 1.0 mm wide; right wing 2.65 mm long, 1.15 mm wide (Figure 21.2); wings hyaline, covered with microtrichia arranged in rows. Stem of M much shorter than fork (0.225 mm to 1.5 mm, left; 0.225 mm to 1.55 mm, right). Branches of anterior fork do not reach wing margin. M and CuA veins without setulae. CuP strong, extending beyond CuA + M 4 furcation.

Legs. Fore coxa, 0.48 mm long; fore and mid femur 0.92 mm and 0.96 mm, respectively [hind femur not observable]; tibia of fore, mid and hind legs, 0.86, 1.18 mm and 1.46 mm in length, respectively; tarsomeres (T1–T5) of fore leg, 1.02– 1.08 mm, 0.52–0.54 mm, 0.36–0.38 mm, 0.28 mm and 0.22–0.24 mm in length, respectively; mid leg tarsomeres (T1–T5), 0.96 mm, 0.48 mm, 0.34– 0.36 mm, 0.22–0.24 mm, and 0.16–0.20 mm in length, respectively; hind leg tarsomeres (T1–T5), 1.04 mm, 0.40 mm, 0.28 mm, 0.20 mm and 0.18 mm in length, respectively (Figure 22.2). All legs with setae in parallel rows. Tibial spurs 1: 2: 2; fore tibial spurs, 0.22–0.23 mm, tibial spurs at midleg 0.27 mm and 0.37 mm long, and tibial spurs at hind leg, 0.38–0.47 mm and 0.59 mm long.

Abdomen and genitalia. Length, 2.35 mm (not counting genitalia), width, 0.7 mm (at tergite 4), uniformly setose. Genitalia, 0.52 mm long, 0.52 mm wide; tergite nine with pair of elongate setae, approximately 0.4 mm long. Dorsal branch of

gonostylus subovate with dorsoapical process measuring 0.09 mm, ventral branch of gonostylus elongate, heavily setose (Figure 22.3).

Allotype. Female unknown.

Syncompressions. None.

Remarks

The large family Mycetophilidae consists of 180 extant genera with 4,150 species and is distributed worldwide. There are 415 known fossil species, the oldest of which date from the earliest Cretaceous. Most (220) of the fossil mycetophilids are Eocene in age. The genus Rymosia s.l. ( Kjaerandsen, 2006; SØli et al., 2000) contains 87 extant species and eight fossil species, six of which are from the Eocene; R. miocenica Lewis, 1969 and R. foersteri Theobald, 1937 date to the Miocene and Oligocene respectively ( PBDB, 2018).

Unfortunately, the original descriptions of R. edwardsi Cockerell, 1921 ( Cockerell, 1921b) , R. ferruginea Cockerell, 1921 ( Cockerell, 1921b) , R. grisea Cockerell, 1921 ( Cockerell, 1921b) and R. rufescens Cockerell, 1921 ( Cockerell, 1921b) , all from the Isle of Wight, were exceedingly terse. None of the specimens was identified as either male or female. All four descriptions, however, were accompanied by a figure of a wing. Rymosia hypnolithica differs from R. edwardsi in that the latter’s wing is 5.1 mm long, two and three times that of the male and a possible female of the new species, respectively. In addition, the wing of R. edwardsi is markedly patterned. The cubital forks of R. ferruginea and R. grisea are quite basal of the medial terminus of r-m whereas these two points are nearly aligned in R. hypnolithica . While the stem of M 1+ 2 in R. grisea is half the length of r-m, in R. hypnolithica , the two are nearly the same length. The wing of R. rufescens is about as long as that of the male of R. hypnolithica , but the wing of R. rufescens (and R. ferruginea ) was reported to be reddish in color. Krzemiński et al. (in press) recently suggested that Rymosia edwardsi Cockerell, 1921 , R. ferruginea Cockerell, 1921 and R. rufescens Cockerell, 1921 , most probably belong to the tribe Mycetophilini . The body of R. longicalcar Meunier 1904 ( Meunier 1904b) is 7 mm long vs. 3.5 mm for R. hypnolithica , its flagellomeres are twice as long as wide, and its cubital fork is distal to its medial fork. Rymosia strangulata Scudder 1890 is a nearly complete specimen, although the apical quarter of the wing and the genitalia are still buried under matrix material. Scudder (1890) stated that “the drawing is incorrect” and, in his figure, Rs and r-m are both missing. He also stated that “the stalk of the upper discoidal vein” as drawn was too long. The specimen is in the collections of Harvard University Museum of Comparative Zoology and a photograph (https://mczbase.mcz.harvard.edu/specimen_images/ entomology/paleo/large/PALE-4967_ Rymosia _strangulata_ type.jpg) clearly shows a short r-m. The ratio of its length to the distance from the beginning of the fork in M to the anterior edge of the wing is 2.3; this ratio is 1.5 in R. hypnolithica .

Paratype specimens of Rymosia hypnolithica provide supportive morphological details. USNM 622565 is a paratype male with a dorsal view of the genitalia; USNM 626133 is a paratype male with black gonostyli with apical process and 9 th (epandrial) sclerite with pair of long bristles. Male specimens USNM 626148 and USNM 621302 may constitute a distinct species, with gonostyli black, of a different form (more compact/elongate), without visible apical process. In addition, leg setation appears relatively longer and antennal segments more compact (not as long relative to width). Unfortunately, these fossils are not preserved with enough morphological detail to merit description of another new species at this time. USNM 623928 (male) represents an additional related, undescribed mycetophilid. Since the mycetophilids found here belong to more than one closely related species, and species are primarily distinguished by male features, the species identity of female USNM 624494 , also an exechiine mycetophilid, remains uncertain .

Figures

FIGURE 21. Rymosia hypnolithica sp. nov., USNM 624134, male. 1, Habitus; 2, Right forewing. Scale bars equal 2.0 mm (1), 1.0 mm (2).

FIGURE 22. Rymosia hypnolithica sp. nov., USNM 624134, male. 1, antennae; 2, Spines and spurs of the legs; 3, Terminalia. Abreviations: lf, lm, lh, rm and rh are left front, left mid, left hind, right mid and right hind legs respectively. Scale bars equal 0.25 mm (1, 3) and 1.0 mm (2).