Tackling the "Protoblattoidea problem": Revision of Protoblattinopsis stubblefieldi (Dictyoptera; Late Carboniferous)

Abstract

The forewing morphology of the fossil species †Protoblattinopsis stubblefieldi Laurentiaux, 1953 (Dictyoptera; Late Carboniferous) is re-investigated. Unlike previously stated, in this species, the stems of R and M are distinct and CuA has branches. The occurrence of the putative plesiomorphies "long ScP" and "differentiated R sectors" (i.e., RA and RP) in †P. stubblefieldi indicates a position basal to all extant Dictyoptera and many members of its paraphyletic stem. Unlike representatives of the families †Archimylacridae and †Blattinopsidae, but similar to Blattodea s. str., †P. stubblefieldi lacks a M-CuA arculus. The comparison of the branching pattern of the median system in †P. stubblefieldi and †Archimylacridae suggests that the arculus of the latter is composed of posterior branches of M. It is noted that the distal location of the point of origin of CuA and CuP, the sigmoid course of the anterior stem of CuA, the strong curvature of CuP, and the occurrence of a short fusion between R/RP and the anterior branch of M are similarities with the representatives of the genus Polyphaga BrullĂŠ, 1835, belonging to Dictyoptera s. str. However, these similar character states are unlikely to be homologous in these taxa, mainly because the hypothesis that Polyphaga is the sister group of the remaining Dictyoptera s. str. (or even Blattodea s. str.) is not strongly supported. Owing to its character state combination, the species †P. stubblefieldi is unique within the "Protoblattoidea waste-basket". Comprehensive studies of wing morphology in stem-Dictyoptera are needed to clarify whether it might be closely related to the lineage from which Dictyoptera s. str. evolved.