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Two new species of Paramesosciophilodes (Diptera, Nematocera, Mesosciophilidae) from the Middle Jurassic of China

Abstract Two new species, Paramesosciophilodes bellus sp. n. and Paramesosciophilodes rarissima sp. n., from the Jiulongshan Formation at Daohugou Village, Inner Mongolia, China, are described in the extinct family Mesosciophilidae. Altogether seven genera with 21 species of mesosciophilids have been described from the Jurassic of Siberia and Kazakhstan, the Lower Cretaceous of Transbaikalia, and the Middle Jurassic of Inner Mongolia. An emended generic diagnosis of Paramesosciophilodes and a list of known taxa of mesosciophilids are provided.


Introduction
Mesosciophilidae is one of the extinct dipteran families of the suborder Nematocera. Rohdendorf (1946) described a species, Mesosciophila venosa, which was assigned to a new subfamily, Mesosciophilinae, within the family Allactoneuridae, along with Fungivoritinae. Later he implicitly synonymized Mesosciophilinae with Fungivoritidae and excluded Allactoneura DeMejere, 1907 from the family (Rohdendorf 1957,  rather than to its previous assignment to the family of Pleciofungivoridae or the family Mesosciophilidae (Zhang 2007).
Here, based on a combination of unique wing venational characters of two recently collected specimens, we describe Paramesosciophilodes bellus sp. n. and Parame-sosciophilodes rarissima sp. n. These specimens with bodies and complete wings were collected from the late Middle Jurassic Jiulongshan Formation of Daohugou Village in the Ningcheng County, Chifeng City, southeastern Inner Mongolia, China. Many well-preserved fossil insects have been described from this locality recently , such as dipterans, neuropterans, orthopterans, heteropterans, etc. (Zhang et al. , 2011Wang et al. 2010;Gu et al. 2012;Yao et al. 2012).

Materials and methods
This study is based on two specimens housed in the Key Lab of Insect Evolution & Environmental Changes, Capital Normal University, Beijing, China (Curator: Dong Ren). The specimens were examined under a LEICA MZ12.5 dissecting microscope. The photos of fossils were taken with a Nikon SMZ1000 stereo microscope. Line drawings were prepared with the aid of CorelDraw 12 graphic software. The method of calculating the ratio of cell r length vs. wing length is as follows: the length of cell r is the length along R 1 , while the length of wing is the length from wing base to wing apex. Wing venation nomenclature follows that of Wootton and Ennos (1989) and Shcherbakov et al. (1995): bRs or dRs = section of R 4+5 basal or distal to r-m, respectively; bM 1+2 or dM 1+2 = section of M 1+2 basal or distal to r-m, respectively. Emended diagnosis. Medium (sized mesosciophilid gnats. Body (including legs) covered with long, dense pubescence. Mesonotum convex. Scutellum sharp, clearly projecting. Wing, Sc 1 elongate, slightly shorter than one-half of wing length (0.43-0.47 times as long as wing length); Sc 2 situated distinctly basad to Rs origin, arising near midway between h to Sc 1 ending; bRs shorter than r-m; R 1 slightly curved; both R 1 and R 4+5 divergent terminally; Rs furcated distad or at level of fork of M 1+2 ; R 2+3 oblique and curved; R 4+5 arched near its midlength; cell r 0.16-0.19 times as long as wing length; stem of M not developed; M 1+2 furcated slightly distad, or basad, to level of Sc 1 ending. Tibiae and tarsi with sparse, short setae. Etymology. The specific name is from the Latin of bellus, meaning beautiful and delicate, for the well-preserved and beautiful specimen.

Paramesosciophilodes bellus
Material. Holotype No. CNU-DIP-NN2013631 p/c, part and counterpart. A well-preserved insect with complete body and two wings but poorly preserved halter, without head, in dorsoventral aspect.
Diagnosis. The Sc 1 ending proximad of the midlength of cell r; bRs 0.7 times of the length of r-m; R 4+5 strongly curved; M 1+2 forking basad of forking of Rs, and distad of the level of Sc 1 ending; CuA strongly arched, reaching the posterior margin of the wing markedly basad of Rs forking to R 2+3 and R 4+5 .
Description of holotype. Medium-sized mesosciophilid with dark body, adult male, in dorsal aspects (Figs 1 and 2A). Wings out-spread, length 5.4 mm, width 2.0 mm. Body length 7.2 mm. Head and antennae not preserved. Thorax convex, length 2.0 mm, width 1.3 mm. Scutellum clearly projecting. Abdomen thin, subcylindrical, length 5.2 mm, width 1.7 mm, approx. 2.6 times as long as head and thorax combined, with eight abdominal segments, first four segments gradually widened distally, last four segments gradually narrowed terminally. Partially preserved male genitalia relatively small, distinctly narrower than eighth abdominal segment. Halters poorly preserved. Legs relatively thin and long, femora clearly thicker in the middle; femora, tibiae and tarsi with two rows of sparse and short setae. Hind leg length 6.3 mm (femur 1.7 mm, tibia 2.4 mm, tarsus 2.2 mm).
Wings membranous, oblong, darker in color in costal area, moderately wide (length 2.7 times of width), and not reaching the apex of abdomen at rest (Fig. 2). C strong, ending beyond wing apex, at which R 4+5 ending. Sc 1 relatively long, approx. 0.4 times the length of wing, ending far distad of the intersection of bRs and r-m. Humeral vein distinct and oblique. Sc 2 well developed, starting in front of bRs. Cell r distinctly small (0.89 mm), approx. 0.165 times the wing length (5.4 mm). Section of R from Sc 2 to bRs origin approx. 2.4 times as long as bRs. R forking into three branches: R 1 , R 2+3 and R 4+5 . R 1 and R 4+5 somewhat divergent terminally; R 2+3 and R 4+5 arched. Forking of Rs distad of the level of M forking. Rs strong, arising from beyond the basal one-third of length of wing, bRs+dRs nearly 0.4 times the R 4+5 . Rs forking to R 2+3 and R 4+5 distad of forking of M 1+2 . Section bRs 0.7 times the r-m. R 1 slightly curved, relatively long (nearly 0.5 times the length of wing), slightly deflected after junction with R 2+3 ; R 2+3 slightly curved, shifted toward wing base, beyond the level of M 1+2 forking. Vein R 4+5 strongly arched near its midway, almost parallel with R 1 , but slightly oblique at apex. Stem of M completely reduced basad of crossvein m-cu, with only a short segment distad of m-cu. Stem of M forking into M 1+2 and M 3+4. M 1+2 forking into M 1 and M 2 near R 2+3 level. M 1 arched anteriorly, M 2 nearly straight. Crossvein r-m short, curved, slightly oblique, shorter than bRs, nearly perpendicular to M 1+2 , almost parallel to R 2+3 , intersected at M 1+2 , forking to bM 1+2 and dM 1+2 . bM 1+2 approx. 6.6 times as long as m-cu. dM 1+2 approx. as long as bM 1+2 , and longer than r-m. CuA running parallel close to M 3+4 basally. CuA reaching the posterior margin of wing at approx. the same level of M 1+2 forking to M 1 and M 2 . CuP short, slightly curved at its midway, not reaching the posterior margin of wing.
Remarks. Paramesosciophilodes bellus sp. n. resembles most closely P. ningchengensis, but can be distinguished from the latter in having Sc 1 ending at C proximad of the miglength of cell r (vs. at the miglength of cell r for P. ningchengensis) and CuA reaching the posterior margin of the wing markedly basad of Rs forking to R 2+3 and R 4+5 (vs. slightly basad of Rs forking to R 2+3 and R 4+5 ).
This new species is differentiated from P. ningchengensis, P. eximia, P. aequus, and P. rarissima sp. n. based on a combination of characters listed in Table 2. Etymology. The specific name is from the Latin word of rarissimus, meaning rare.

Paramesosciophilodes rarissima
Material. Holotype No. CNU-DIP-NN2013145 p/c, part and counterpart. A well-preserved insect with complete body with two wings, without head and halters, in dorsoventral aspect.
Diagnosis. Sc 1 ending near the midlength of cell r; bRs 0.8 times the r-m; R 4+5 strongly curved; M 1+2 forking basad of R 2+3 level and distad of level of Sc 1 ending at C; CuA strongly arched, reaching the posterior margin of the wing at the level of intersection of Rs forking to R 2+3 and R 4+5 .
Description of holotype. Medium-sized mesosciophilid gnats, in dorsal aspect (Figs 3 and 4A). Body length (without head and part of thorax) 7.2 mm as preserved. Legs covered with long, dense pubescence. Head, antennae, and halters not preserved. Thorax length 1.8 mm, width 1.5 mm. Mesonotum convex. Scutellum sharp, clearly projecting. Wings membranous, oblong, length 5.0 mm, width 2.2   mm, darker in color in costal area, length 2.3 times width, and not reaching the apex of abdomen at rest. Abdomen thin, subcylindrical, length 5.4 mm, width 1.5 mm, with first five segments gradually widened distally, other segments gradually narrowed terminally. Legs poorly preserved, femora thicker in the middle, covered with numerous setae. C strong, ending beyond wing apex, at which R 4+5 ending (Fig. 4). Sc converging with C before the level of R 4+5 . Sc 1 elongate, slightly shorter than one-half of wing length (0.43-0.47 times the wing length), and ending far distad of the intersection of bRs and r-m. Vein h distinct and oblique. Sc 2 developed well, starting in front of Rs, situated distinctly basal to Rs origin, arising beyond midway between h to Sc 1 ending. Cell r relatively large (0.92 mm), approx. 0.18 times the wing length (5.0 mm). The section of R from Sc 2 to Rs origin approx. 0.7 times the section bRs. R forking to R 1 and Rs, then Rs to R 2+3 and R 4+5 . Both R 1 and R 4+5 somewhat divergent terminally; R 2+3 and R 4+5 arched. Rs usually strong, arising from basal one-half of length of wing, forking to R 2+3 and R 4+5 beyond the forking of M 1+2 . Section bRs 0.8 times the r-m. R 1 slightly curved, relatively long, nearly 0.5 times the wing. Both R 1 and R 4+5 divergent terminally. R 2+3 curved, beyond the level of M 1 and M 2 forking. R 4+5 strongly arched near its midlength. Stem of M, basad to crossvein m-cu completely reduced, with only a short segment distal to m-cu. Stem of M forking into M 1+2 and M 3+4 . M 1+2 forking into M 1 and M 2 basad of R 2+3 level and distad to level of Sc 1 ending at C. M 1 arched cephalad. M 2 nearly straight. Crossvein r-m short, curved, slightly oblique, shorter than bRs, r-m intersecting M 1+2 and dividing M 1+2 into bM 1+2 and dM 1+2 . Section bM 1+2 approx. 4.3 times the crossvein m-cu. Section dM 1+2 approx. 1.2 times the section bM 1+2 , and longer than r-m. CuA running parallel and close to M 3+4 basally. CuP short, slightly curved midway, reaching the posterior margin of wing at the same level as Sc 1 ending at C.
Remarks. Paramesosciophilodes rarissima sp. n. is distinguished from all other species of Paramesosciophilodes based on a combination of characters listed in Table 2.

Discussion
As shown in Table 1, a total of 7 genera and 21 species of mesosciophilids have been reported from various localities in the Jurassic of Siberia and Kazakhstan, Lower Cretaceous of Transbaikalia, and Middle Jurassic of Inner Mongolia. One genus with 2 species was described in the Middle Jurassic Itat Formation, Siberia; 6 genera with 13 species were reported from the Middle Jurassic Jiulongshan Formation of Daohugou, Inner Mongolia, China; 2 genera with 3 species were described from the Late Jurassic Karabastau Formation in Kazakhstan; and one genus with 3 species was documented from the Early Cretaceous Zaza Formation at Baissa, Transbaikalia.
The data show that the known earliest mesosciophilids have been reported from the Middle Jurassic, while the latest ones are described from the Early Cretaceous. It seems that mesosciophilids became less diverse in the Early Cretaceous, and were possibly replaced by Mycetophilidae (Blagoderov 1993), which is supported by Zhang's data, who listed all the mesosciophilids and mycetophilids from Daohugou, and compared them with other faunas (Zhang 2002).