Four new species of hangingflies (Insecta, Mecoptera, Bittacidae) from the Middle Jurassic of northeastern China

Abstract Two new species of Mongolbittacus Petrulevičius, Huang & Ren, 2007, Mongolbittacus speciosus sp. n. and Mongolbittacus oligophlebius sp. n., and two new species of Exilibittacus Yang, Ren & Shih, 2012, Exilibittacus foliaceus sp. n. and Exilibittacus plagioneurus sp. n., in the family Bittacidae, are described and illustrated based on five well-preserved fossil specimens. These specimens were collected from the late Middle Jurassic Jiulongshan Formation of Daohugou, Inner Mongolia, China. These new findings enhance our understanding of the morphological characters of early hangingflies and highlight the diversity of bittacids in the Mid Mesozoic ecosystems.


Introduction
Bittacidae, a large family of Mecoptera commonly called hangingflies, live mainly in the temperate or warm tropical climates. The fifth tarsomere of bittacids can be folded against the fourth with the only one claw at pretarsus (Petrulevičius et al. 2007). Since this special tarsi structure is shared by a sister group of Cimbrophlebiidae (Archibald 2009;Yang et al. 2012a), it is suggested that this morphological character may be

Material and methods
The fossil specimens were examined with a Leica M165C dissecting microscope and illustrated with the aid of a camera lucida attached to the microscope; drawings were scanned into a computer by EPSON5100 and were edited with Adobe Photoshop® CS3. Photographs of the specimens and magnified images of the details were taken with a digital camera system attached to the Leica M165C. Specimens were at times treated with ethanol (95%) on the surface to enhance the clarity and contrast. All type specimens are deposited in the Key Lab of Insect Evolution and Environmental Changes, the College of Life Sciences, Capital Normal University, Beijing, China (CNUB, Ren Dong, Curator). The wing venation nomenclature follows Byers (1979). The term of 'bittacid cross' is defined as the crossveins of [R 4+5 -M 1+2 , M 1+2 -M 3 ] (Bechly and Schweigert 2000).
Diagnosis. In forewing, Sc reaching the anterior margin proximad of the forking of Rs; one crossvein between C and R 1 ; 1A and 2A fusing at base; and 2A sharply curving to the posterior margin.
Description. A male specimen in lateral view. The head oviform with robust and slender chewing mouthparts. Compound eyes large and oval. Antennae almost complete, filiform, about 6.9 mm long, comprising about twenty antennomeres; the lengths of basal antennomeres almost the same, but several apical antennomeres shorter than the basal ones. Thorax divided into pronotum, mesonotum and metanotum from the lateral view (Figs 1A-C, 4B, F).
Legs. Long and slender in lateral view, densely covered with short setae. But all legs fragmented due to poor preservation. Mesocoxa, metacoxa, trochanter visible in lateral view. Mid tibia 4.4 mm; tibial spurs long and sharp. Tarsus with 5 tarsomeres and a single pretarsal claw, but the fifth tarsomere not folded against the fourth as  preserved. In addition, the second and third tarsomeres covered with a few small spines ( Fig. 1A-D).
Forewing. No maculation, base of wing narrow. Sc short, one oblique subcostal crossvein (Scv) between Sc and R 1 ; one crossvein between R 1 and C; R 1 smooth and reaching the dark pterostigmal area; Rs originating from R 1 at an acute angle; one crossvein between R 1 and R 2+3 , one crossvein between R 2+3 and R 4 and one crossvein between R 4 and R 5 ; the 'bittacid cross' not aligned, Z-shaped (in side view), and posterior part of 'the 'bittacid cross' distad of the forking of M 3+4 ; M with four branches and bifurcating proximad of the forking of Rs; one crossvein between R 5 and M 1 , one between M 1 and M 2 and one between M 2 and M 3 ; M 4 simple, one long and oblique crossvein between M 4 and Cu 1 ; Cu 1 and M overlapping at base for a short distance; Cu 2 curving sharply with a 90° angle, reaching the posterior margin; Cu 1 and Cu 2 almost parallel, with three crossveins between them, the first oblique crossvein located at the base of the wing, the second at the level of Scv, and the third near the sharp bending of Cu 2 . Veins 1A and 2A fusing at base, 1A reaching the posterior margin proximad of the origination of Rs from R 1 ; two crossveins between 1A and Cu 2 ( Hind wing. Sc short, reaching the anterior margin proximad of the forking of Rs; one crossvein between R 1 and C; One subcostal crossvein (Scv) between Sc and R 1 , one crossvein between R 1 and R 2+3 , and one short crossvein between R 2+3 and R 4 ; R 4 sharply bending upwards, then parallel with R 5 , one crossvein between them; the 'bittacid cross' not aligned, Z-shaped; M forking proximad of the bifurcation of Rs; one crossvein between R 5 and M 1 , one between M 1 and M 2 , one between M 2 and M 3 and one oblique crossvein between M 4 and Cu 1 ; Cu 1 and Cu 2 almost parallel with two crossveins between them; Cu 2 bending sharply with an 90° angle at the level slightly proximad of the forking of M 3+4 ; one crossvein between Cu 2 and 1A (Figs 2E-H, 3B). Abdomen. Abdomen 6.5 mm long, with 9 visible segments. The ninth tergum (T9) connecting gonocoxite with dense short setae at the apex, epiandrium well-preserved with long setae on the surface; procitiger and cercus present in lateral view (Figs 1A-C, 4A, C).
Remarks. Mongolbittacus speciosus sp. n. (Figs 1-4) is assigned to the genus Mongolbittacus based on the following generic diagnostic characters: R 4+5 plus R 4 distinctively curved; M 4 simple; the 'bittacid cross' not aligned; wide posterior anal field; and the forking of M proximad of the Rs forking. M. speciosus sp. n. is distinguished from the other two species of Mongolbittacus by veins of 1A and 2A fusing at base, and 2A sharply curving to the posterior margin, as shown in the key below. Diagnosis. The posterior part of the "bittacid cross' coinciding with the forking of M 3+4 ; one oblique crossvein between R 2+3 and R 4 at the bifurcation of R 2+3 ; and length of R 3 0.9 times as long as R 2+3 .
Description. Poorly preserved with only one complete forewing and the basal part of one hind wing. But the mid-tibia with two long spurs and five tarsomeres wellpreserved, covered by dense short setae (Fig. 5A, B, D).
Forewing. Sc reaching the anterior margin proximad of the forking of Rs, one crossvein between C and R 1 ; one subcostal crossvein (Scv) between Sc and R 1 ; Rs bifurcating into four branches, one crossvein between R 1 and R 2+3 and one oblique crossvein between R 2+3 and R 4 ; Rs arising from R 1 at an acute angle; length of R 3 0.9 times as long as R 2+3 ; one crossvein between R 4 and R 5 ; M with four branches and bifurcating proximad of the forking of Rs; the 'bittacid cross' not aligned; the posterior part of the 'bittacid cross' coinciding with the forking of M 3+4 ; one crossvein between R 5 and M 1 , one between M 1 and M 2 and one between M 2 and M 3 ; one crossvein between Cu 1 and M 4 , Cu 1 and Cu 2 parallel with two crossveins between them; one crossvein between Cu 2 and 1A; 1A reaching the posterior margin distad of the origination of Rs from R 1 ; 2A bending sharply and reaching the posterior margin, a short crossvein between 1A and 2A (Figs 5C, E, 6C).

Remarks.
Mongolbittacus oligophlebius sp. n. (Figs 5, 6) is assigned to the genus Mongolbittacus based on the following generic diagnostic characters: R 4+5 plus R 4 distinctively curved; M 4 simple; the 'bittacid cross' not aligned; posterior anal field broad; and 2A bending sharply and reaching the posterior margin. This new species is differentiated from M. daohugoensis and M. speciosus sp. n. by characters as shown in the key below.   Forewing: Sc reaching the anterior margin at the same level or proximad of the forking of R 4+5 ; the 'bittacid cross' aligned, the posterior of the 'bittacid cross' distad of the bifurcation of M 3+4 ; 1A terminating at the posterior margin at the same level or distad of the origination of Rs from R 1 . Hind wing: Rs with three or four branches, M with three branches and 2A absent.
Diagnosis. Forewing: pterostigmal crossveins (Pcv) absent, but 2A present. Hind wing: Rs with four branches and the bifurcation of Rs at the same level of the bifurcation of M.
Description. A female holotype preserved in dorsal view. Antenna filiform, scape, pedicel and part of other antennomeres preserved. The vertex of the head raised. Legs not well-preserved, covered with short setae; the fifth tarsomere folded against the fourth, a claw present (Fig. 7A, B).
Forewing. The base of wings narrow, pterostigma slightly dark. Sc terminating at the anterior margin proximad of the R 4+5 forking; one subcostal crossvein (Scv) between Sc and R 1 ; R 1 running straight through pterostigma, without sagging; one crossvein between R 1 and R 2+3 ; Rs with four branches, R 4 slightly curved at beginning and then parallel with R 5 ; one crossvein between R 2+3 and R 4 and one crossvein between R 4 and R 5 ; M with four branches, M 3+4 forking far proximad of the bifurcation of M 1+2 ; the 'bittacid cross' aligned and gently curved, posterior part of the 'bittacid cross' reaching M 3 distad of the M 3+4 forking point; one crossvein between R 5 and M 1 , one between M 1 and M 2 and one between M 2 and M 3 ; Cu 1 and Cu 2 almost parallel with two crossveins between them, one crossvein between M 4 and Cu 1 ; 1A and 2A simple and one crossvein between them; 1A reaching the posterior margin at the same level of the origination of Rs from R 1 ; 2A reaching the posterior margin at the same level of the origination point of M (Fig. 7C).
Hind wing. With the same shape as the forewing. R 1 running smoothly through pterostigma; pterostigmal crossveins (Pcv) absent; Rs with four branches; one crossvein between R 2+3 and R 4 and one between R 4 and R 5 ; the 'bittacid cross' aligned; M divided into three branches; two crossveins between R 5 and M 1 , one between M 1 and M 2 , one between M 2 and M 3 and one between M 3 and Cu 1 ; Cu 1 and Cu 2 parallel and with one crossvein between them. Vein 1A reaching the posterior margin at the level slightly proximad of the Rs originating from R 1 , one crossvein between Cu 2 and 1A (Fig. 7D).
Abdomen. Abdomen 9.1 mm long, with ten visible segments. Female genital structure well-preserved from the dorsal view. Supraanale and cercus covered with small and short setae (Fig. 7A, B, E, F).
Remarks. Exilibittacus foliaceus sp. n. (Fig. 7) is assigned to the genus Exilibittacus Yang, Ren & Shih, 2012 based on the following generic diagnostic characters: in forewing, Sc reaching the anterior margin proximad of the forking of R 4+5 and the 'bittacid cross' aligned; and in hind wing, Rs with four branches while M with three branches. Exilibittacus foliaceus sp. n. is distinguished from the other two species as shown by the key below.
Holotype. Female, CNU-MEC-NN2013013 P/C, in dorsal view. Abdomen length 8.3 mm, forewing length 9.3 mm with a maximal width of 2.3 mm; hind wing length 8.4 mm with a maximal width of 2.2 mm.
Diagnosis. Forewing Sc terminating at the anterior margin at the same level of the R 4+5 forking; Vein 1A terminating at the posterior margin distad of the origination of Rs from R 1 .
Description. Female, small-sized, head not preserved but mesothorax and metathorax preserved. Legs partially preserved, one hind leg with five tarsomeres present but the pretarsal claw not preserved, the fifth tarsomere folded against the fourth; the first and second tarsomeres with several spines. (Fig. 8A-D) Forewing. Wing narrow basally with obviously dark pterostigma. Sc long, reaching the anterior margin at the same level of the R 4+5 forking; R 1 not forking, one subcostal crossvein (Scv) between Sc and R 1 , Scv about 1/6 as long as the Sc length between Scv and the apex of Sc; one pterostigmal crossvein (Pcv) and one crossvein between R 1 and R 2+3 ; Rs with four branches, one crossvein between R 3 and R 4 , one between R 2+3 and R 4 and one between R 4 and R 5 ; M with four branches, M 4 base bending sharply; the 'bittacid cross' aligned, the posterior part of the 'bittacid cross' reaching M 3 distad of the M 3+4 forking point; two crossveins between R 5 and M 1 , one between M 1 and M 2 and one between M 2 and M 3 ; Cu 1 ending before the forking of R 4+5 , one crossvein between M 4 and Cu 1 , one between Cu 1 and Cu 2 ; one short crossvein between Cu 2 and 1A; 1A terminating at the posterior margin distad of the origination of Rs; 2A ending proximad of the originations of Rs and M, one crossvein between 1A and 2A (Fig. 9A, C).
Hind wing. Sc short, reaching the anterior margin before the forking of R 4+5 , one crossvein (Scv) between Sc and R 1 ; R 1 smooth and not sagging through the pterostigmal area; one pterostigmal crossvein (Pcv) present. Rs with three branches; one crossvein between R 1 and R 2 , one between R 2 and R 3 and one between R 3 and R 4 ; M with three branches; two crossveins between R 4 and M 1 , one between M 1 and M 2 and one between M 2 and M 3 ; the 'bittacid cross' not aligned; one between M 3 and Cu 1 and one between Cu 1 and Cu 2 . Vein 1A terminating at the posterior margin distad of the origination of Rs, one crossvein between Cu 2 and 1A (Fig. 9B, D).
Abdomen. Ten segments visible, genital segments not preserved ( Fig. 8A-C). Remarks. Exilibittacus plagioneurus sp. n. (Figs 8, 9) is assigned to Exilibittacus Yang, Ren & Shih, 2012 based on the following generic diagnostic characters: in forewing, Sc reaching the anterior margin at the same level of the forking of R 4+5 and the 'bittacid cross' aligned, and in hind wing, M with three branches. The new species is differentiated from E. lii and E. foliaceus sp. n. by characters shown in the key below.

Key to species of Exilibittacus based on characters of both fore-and hind-wings
1 Rs with four branches in hind wing (Fig. 7D) 1A terminating at the posterior margin of the forewing distad of the origination of Rs (Fig. 9A)