Fig. 4

Several examples of the fossil insects with the wings possessing venational asymmetry reported from the Mesozoic of China. a–c, Paristopsyche angelineae within Mecoptera showing the different branches of vein MP3 between left and right forewings. a, photograph of the specimen; b, line drawing of left forewing, vein MP3 with typical one branch; c, line drawing of right forewing, vein MP3 with two branches. d–g, Exilibittacus lii within Mecoptera showing the different vein RP and MP on fore and hind wings. D, photograph of the specimen. e and f, right and left forewings with RP1+2 forking and MP with four branches. g, left hind wing with RP1+2 not forking and MP with three branches. h–j, Synapocossus sciacchitanoae within Hemiptera showing the RP coalesced with M1 on right and left forewings. h, photograph of the specimen. i, left wing with the Rs coalesced with M1 at a point. j, right wing with the RP coalesced with M1 for about 1 mm. k–m, Sinosharaperla zhaoi within Plecoptera showing different Rs forking on right and left forewings. k, photograph of the specimen. l, part of right hind wing showing Rs with two terminal branches. m, part of left hind wing, Rs with only one branch. Scale bar represents 5 mm (h and k), 2 mm (a–d), 1 mm (e–g, i, j, l and m)