Variability and symmetry of a Jurassic nocturnal predatory cockroach (Blattida: Raphidiomimidae)

Abstract

Cockroaches are as of yet the only animal group with a fossil record complete enough to reveal\nthe quantitative changes of individual intraspecific variability over a considerable interval of time (320\nMa). Ninety three individuals of the first known nocturnal and/or crepuscular carnivorous cockroach\nDivocina noci gen. et sp. nov. of the family Raphidiomimidae (Middle Jurassic Jiulongshan Formation;\nDaohugou, Inner Mongolia Province, China) now reveal the comparison of variability and symmetry of\nright and left wings separately. The sole significant difference is the more pronounced variability of the\nanterior part (involved in flight) of the left forewings, which may be the consequence of the superposition\nof the left wing and its protective function associated with vein reorganizations.\nThe overall variability coefficient of the number of veins in the distal forewing margin and total\nnumber of veins at the margin (CVtotal= 7.65; hindwing CVtotal= 7.54) was low when compared with the\nwing centre, which together with wing symmetry suggest comparatively good flight. The total number\nof veins is in perfect congruence with the variability of Fortiblatta cuspicolor Liang, Vrsanský and Ren,\n2009- another raphidiomimid from the same locality (CVtotal = 7.70; hind wing CVtotal= 7.33). In spite of\nnearly identical overall variability, data for respective veins vary up to 30%. Different also is the mean\nasymmetry expressed as the difference in the number of veins meeting at the margin between the respective\nsides (4.7% of Divocina vs 7.0% of Fortiblatta cuspicolor). It follows that the general variability is to a\nlarge extent independent of variability of respective characters as well as of symmetry values.