Salishomyia eocenica Bickel, 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 : 32-33

Salishomyia eocenica Bickel , sp. nov.

Figure 27

zoobank.org/ ACCE57D9-7CDD-49F8-ADAF-8E2674E9124A

Etymology. The specific epithet refers to this species’ occurrence in the Eocene period.

Description

Male, body length: 1.7 mm (Figure 27.1).

Head. Ovate in lateral view; dorsal postcranium concave and appearing to partially enclose anterior mesonotum; palp with short apical seta; proboscis short, subrectangular; antenna short; postpedicel subrectangular and rounded (possibly reniform) with apical arista; arista threadlike and shorter than head height.

Thorax. Dark brown to black; dorsal setae (probably dorsocentral setae) evident; posterior mesononotum distinctly flattened, scutellum with distinct lateral and median setae.

Leg. Coxa I apparently infuscated basally, with coxae II and III yellowish; remainder of legs apparently yellow, with little evident setation and no indication of anterior preapical setae on femora II and III; [relative lengths of podomeres are representative ratios, not measurements and given in the following formula and punctuation for each leg: femur; tibia; tarsomere 1/ 2/ 3/ 4/ 5]; leg I: 3.7; 3.6, distal podomeres obscured; leg II: all podomeres obscured; leg III: 4.0; 3.4; 1.0/ 1.2/ 0.6/ 0.4/ 0.4.

Wing. Length and width, 1.4 and 0.7 mm (Figure 27.2); hyaline, C reaches wing apex, joining vein M; R 2+3 joining costa at 5/6 distance from base; R 4+ 5 in gentle anterior arc and joining costa just anterior to wing apex; M basally diverging from R 4+5, and at midlength with gentle bend to arch towards R 4+5 with the two veins becoming subparallel in distal sixth of wing, and M joining margin at apex; crossvein dm-m positioned basally, with ratio of length of dm-m crossvein/distal section M 4 = 0.3; lower calypter and halter not visible.

Abdomen. Tergites with only short setation, without long marginal setae; tergite one short and adjacent to metapostnotum; tergites two to five each well-developed, with corresponding sternite; tergite six prominent; hypopygium spheroidal with short digitiform surstylus; cercus subtriangular; hypandrium (or phallus?) curved and projecting beyond hypopygium near sternite 5.

Allotype. Female unknown.

Syncompressions. None.

Remarks

The family Dolichopodidae comprises some 7,300 species in 230 genera in the recent fauna. It is often rich and abundant in Tertiary amber deposits, a result of their use of tree trunks for both feeding and mating, thereby increasing their chance of becoming entrapped by resin flows. Dolichopodids are also numerous in marine and lacustrine littoral habitats and correspondingly are known as compression fossils from a number of fine-grained lacustrine deposits. The new genus Salishomyia from the Kishenehn Formation clearly belongs to the dolichopodid subfamily Medeterinae , based on the following characters: antenna short; postpedicel subrectangular and rounded (possibly reniform) with apical arista, dorsal postcranium concave; posterior mesonotum apparently flattened; legs without strong setation, femora II and III without preapical setae, hypopygium large and external, not enclosed by anterior postabdominal segments. Salishomyia appears to have a classical Medetera - like venation, with vein M basally diverging from R 4+5, and at midlength bending gently to arch forward towards vein R 4+5. However, in Medetera , the dm-m crossvein connects M 4 with M at the bend in vein M, while in Salishomyia , the dm-cu crossvein is positioned basad of the vein M bend, and the wing is broader. This wing character is diagnostic for Salishomyia .

The Kishenehn Formation dolichopodid fauna, as of 2017, consists of 78 specimens. Other than Salishomyia eocenica , 30 additional specimens are of potential interest. Among these are two species in a genus near Hercostomus Loew (possibly Gymnopternus Loew ), one with six males (USNM 621409, 622506, 622656, 625273, 625526 and 626174) and the other with one male (USNM 621182) and two females (USNM 622026 and 624021) of uncertain specific association. The two species can be separated by the shape of surstyli projecting from the hypopygium. Hercostomus acts as a cosmopolitan “holding genus” for many described species and remains poorly defined and is undoubtedly a polyphyletic assemblage ( Brooks, 2005). Although additional work is needed to resolve the phylogenetic relationships of this complex cosmopolitan genus, it is important to note the presence of Hercostomus -like species in the Kishenehn formation to demonstrate regional historicalbiogeographical relationships. The genus Gymnopternus is closely related to Hercostomus ; Gymnopternus lacustris was described from the Miocene Florissant beds of Colorado ( Bickel, 1995).

There are a number of additional specimens that are of interest but lack critical morphological detail. These include: 1) a species with some similarities to the recent genus Chrysotimus Loew but with a slighter build and an enlarged hypopygium (12 specimens, both males [USNM 620106, 620817, 621111, 622587 and 623229] and females [USNM 621246, 621939, 623788, 623828, 624434, 712964 and 712965]), 2) a species where veins R 4+5 and M bowed with respect to each other beyond the dm-m crossvein (three females [USNM 609598, 624638 and 712963] and one male [USNM 620605]), 3) a species with similar venation to “ Chrysotus molestus Meunier ” (which is not in the genus Chrysotus ) from Baltic amber, with a

wide wing and vein M ending well behind the wing apex (two females [USNM 620633 and 620464] and a possible male [USNM 620994]), 4) a species possibly near the abundant Baltic amber genus Palaeomedeterus Meunier (one male [USNM 624586]), and 5) a species appearing similar to the recent genus Rhaphium Meigen (one male [USNM 620398]).

Figures

FIGURE 27. Salishomyia eocenica sp. nov., USNM 622501. 1, Habitus; 2, Right wing. Scale bars equal 1.0 mm (1) and 0.5 mm (2).