Brevitrichia messogenes Greenwalt and Winterton, 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 : 24-27

Brevitrichia messogenes Greenwalt and Winterton sp. n.

Figures 14-15

zoobank.org/ 2DC66356-B877-4D33-B68D-A2C3A9717D91

Type species. Pseudatrichia griseola Coquillett,1900 , by original designation.

Holotype. Female, USNM 620163 , deposited in the Department of Paleobiology , National Museum of Natural History ( NMNH), Smithsonian Institution, Washington, District of Columbia, USA.

Locality and horizon. Park 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 Greek, messogenes , middle aged, relating to the Paleogene age of the deposit bearing this fossil.

Diagnosis. Brevitrichia messogenes is the first described fossil species of the rather species-rich New World genus Brevitrichia . Most species of

PALAEO- ELECTRONICA.ORG

Brevitrichia are pale colored, frequently with a fine, grayish cuticular surface texture. Brevitrichia messogenes differs from these by the apparent uniformly dark body coloration. Additional discriminating features are lacking to enable further differentiation from other species in the genus.

Description (female). Black to brown, body length 4.0 mm ( Figure 14A ). Head dark brown/black, subspherical, 0.52 mm long, 0.48 mm high, flat ventrally; eye oval, 0.3 mm wide, 0.37 mm high; antenna short, 0.28 mm long, pedicel 66 μm high, 55 μm long, F1 0.18 mm long, slightly diamond-shaped, 92 μm maximum width, 33 μm at concave

GREENWALT ET AL.: KISHENEHN FORMATION DIPTERA terminus Figure 14B ). Thorax black, 0.89 mm long; wing short, not reaching tergite 7, 2.0 mm long, 0.65 mm wide, wing/body length = 0.5; C and R 1 pigmented though pigmentation increasingly weak posteriorly, C setose with terminus at wing apex and R 5 +M 1, distance between Sc and R 1 equal to that between R 1 and R 2+3, R 4 origin in distal third of cell r 5, cell dm 0.5 mm long, M 1 fused with R 5, CuA distinctly recurved to meet CuA+CuP, M 4 meeting wing margin ( Figure 15 A-B). Fore, mid and hind femora, tibiae and tarsi 0.33, NA, 0.6, 0.43, 0.54, 0.72, 0.42, 0.50 and 0.52 mm, respectively; fore leg tarsomeres 1-5 0.16 mm, 78 μm, 63 μm, 49 μm, 67 μm? respectively. Abdomen dark brown, 2.73 mm long, maximum basal width twice terminal width; posterior edge of tergite 8 heavily spinose, tergite 9+10 0.18 mm long, with acanthophorite spines about 80 μm long, cercus without setae, about 25 μm wide ( Figure 14C ).

Male. Unknown.

Synimpressions. Dipteran pupae

Remarks. The family Scenopinidae contains 25 genera and approximately 420 species that have been separated into three distinct subfamilies ( Winterton and Ware, 2015). The tribe Metatrichini , one of two in the subfamily Scenopininae , is distinguished from all other scenopinids by R 5 merged with M 1. The tribe contains 183 extant species in 14 genera, many endemic to the Southern Hemisphere ( Winterton and Gaimari, 2017). Three fossil species have been assigned to the family – all differ markedly from B. messogenes . Metatrichia pria Yeates and Grimald, 1993 was described from two female specimens in amber from the Dominican Republic. They are large, 7.6 mm in length, and have M 1 fused with R 5. The species is characterized by a bulging face, wing extending beyond abdomen; wing/body ratio = 0.57 vs. 0.48 for B. messogenes , R 4 fork origin in basal third of cell r 5 and at the level of the termination of R 2+ 3 in C ( Yeates and Grimaldi, 1993). Eocenotrichia magnifica Garrouste, Azar and Nel, 2016 is from the lowermost Eocene amber of Le Quesnoy, France ( Garrouste et al., 2016). Garrouste et al. (2016) keyed E. magnifica to the extant genus Propebrevitrichia Kelsey, 1969 but noted its larger size (> 7 mm vs. <4 mm) and tergite 8 slightly longer than sternite 8 and, as a result, created the new genus Eoceotrichia . The specimen is 7.6 mm in length, with M 1 fused with R 5, wing/body ratio = 0.57, R 4 fork origin in distal third of cell r 5 and R 4 distal to the termination of R 2+ 3 in C. A third and much older species, Proratites simplex Grimaldi and Cumming, 1999 , is from 90-94 MA New Jersey amber; unlike M. pria and E. magnifica , it does not have M 1 fused with R 5 and, as such, does not belong to Metatrichini ( Grimaldi and Cumming, 1999). It differs from all extant Scenopinidae in having a long thin arista-like stylus four times as long as the postpedicel. Winterton and Ware (2015) have argued that P. simplex cannot be conclusively placed in Scenopinidae .

The presence of acanthophorite spines, well-developed mouthparts, fused M 1 +R 5, relatively narrow abdomen, and relatively small size place this new fossil species in Metatrichini among the group of genera comprising Brevitrichia Hardy, 1944 , Heteromphrale Kröber, 1937 , Irwiniana Kelsey, 1971 , Propebrevitrichia Kelsey, 1969 , Paramonova Kelsey, 1970 and Riekiella Paramonov, 1955 ( Winterton and Ware, 2015). Specifically, this species is placed in the New World genus Brevitrichia as it exhibits the following (female) characteristics: mouthparts well developed, M 1 and R 5 fused apically, acanthophorite spines well developed but not tufted apically, body size relatively small and abdomen not broadly flattened. The shape of sternite 8 helps differentiate B. messogenes from Irwiniana and Heteromphrale as it is slightly rounded apically, resembling that of other species of Brevitrichia . Sternite 8 in Irwiniana is trilobate apically, or elongated in Heteromphrale ( Winterton and Gharali, 2011; Winterton and Gaimari, 2011). Based on the angle this specimen was preserved, the characteristic rounded lateral lobes typically found in Brevitrichia are not readily apparent. In addition, wing R 4 diverges from R 5 along the basal half of cell r 3 in Heteromphrale and Brevitrichia compared to along the distal half of the cell in Propebrevitrichia, Riekella , Irwiniana , Paratrichia and Paramonova . Brevitrichia messogenes displays the diverging R 4 from R 5 in the distal half of the cell, suggesting that the utility of the character in isolation may be questionable. Brevitrichia messogenes is differentiated from extant Brevitrichia species by the uniformly dark coloration, as most species are pale coloured. Few other discriminating characters are evident in this fossil.

Figures

FIGURE 14. Brevitrichia messogenes Greenwalt and Winterton sp. n., USNM 620163, female. A, Habitus; B, Head and antennae; C, Genitalia. Scale bars equal 1.0 mm (A), and 0.2 mm (B, C).

FIGURE 15. Brevitrichia messogenes Greenwalt and Winterton sp. n., USNM 620163. A, Left wing; B, wing, drawing. Scale bar = 1.0 mm.