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

  • Jun-Hui Liang
  • Peter Vršanský
  • Dong Ren
Keywords: insects, fossil cockroaches, Bathonian, Middle Jurassic, nocturnal, Raphidiomimidae, predators


Cockroaches are as of yet the only animal group with a fossil record complete enough to reveal the quantitative changes of individual intraspecific variability over a considerable interval of time (320 Ma). Ninety three individuals of the first known nocturnal and/or crepuscular carnivorous cockroach Divocina noci gen. et sp. nov. of the family Raphidiomimidae (Middle Jurassic Jiulongshan Formation; Daohugou, Inner Mongolia Province, China) now reveal the comparison of variability and symmetry of right and left wings separately. The sole significant difference is the more pronounced variability of the anterior part (involved in flight) of the left forewings, which may be the consequence of the superposition of the left wing and its protective function associated with vein reorganizations. The overall variability coefficient of the number of veins in the distal forewing margin and total number of veins at the margin (CVtotal= 7.65; hindwing CVtotal= 7.54) was low when compared with the wing centre, which together with wing symmetry suggest comparatively good flight. The total number of veins is in perfect congruence with the variability of Fortiblatta cuspicolor Liang, Vršanský and Ren, 2009– another raphidiomimid from the same locality (CVtotal = 7.70; hind wing CVtotal= 7.33). In spite of nearly identical overall variability, data for respective veins vary up to 30%. Different also is the mean asymmetry expressed as the difference in the number of veins meeting at the margin between the respective sides (4.7% of Divocina vs 7.0% of Fortiblatta cuspicolor). It follows that the general variability is to a large extent independent of variability of respective characters as well as of symmetry values.