Figure 3.

(A) Number of costal cross veins in the forewing of 34 species of stoneflies from 13 families. Filled circles represent taxa from the basal superfamily Nemouroidea, open circles represent taxa from the more derived clades; squares represent fossil species (see D; these were excluded from the statistical analyses). (B) Mean residual (+SE) number of costal cross veins in forewings of the two basal clades (“B”) vs. the more derived clades (“D”; P = 0.009); residuals are from the regression of costal cross vein number on wing length. (C) Number of cubital cross veins as a function of wing length. There was no significant difference in residual values for cubital cross veins in basal vs. derived taxa (P = 0.39). (D) Drawings of the earliest known fossil stonefly wings [≈260 million years ago; reproduced with permission from ref. 12 (Copyright 1965, Annual Reviews)].