At last, a Pennsylvanian stem-stonefly (Plecoptera) discovered

Abstract

Background: Stem-relatives of many winged insect orders have been identified among Pennsylvanian fossils (Carboniferous Period). Owing to their presumed 'basal' position in insect phylogeny, stoneflies were expected to occur at this period. However, no relative has ever been designated convincingly.

Results: In this paper, we report specimens belonging to a new fossil insect species collected from the Tupo Formation (Pennsylvanian; China). The wing venation of Gulou carpenteri gen. et sp. nov. exhibits character states diagnostic of the order Plecoptera, but lack character states shared by unequivocal representatives of the order. Derived from this identification, the delimitation of the fossil species is ascertained based on comparison of several extant stonefly species. This comparative analysis allowed a trait present in G. carpenteri gen. et sp. nov., but rarely occurring in extant species, to be documented and highlighted as atavistic. Affinities of taxa formerly proposed as putative stem-stoneflies are reconsidered in the light of the new discovery.

Conclusions: Gulou carpenteri gen. et sp. nov. is considered the only genuine Plecoptera reported from the Pennsylvanian. Continuing efforts on the systematics of Pennsylvanian winged insects indicate a fauna more diverse than previously appreciated. It suggests that insects already had a long, yet undocumented, history by this time.

Figure 1

Gulou carpenteri gen. et sp. nov. (Pennsylvanian; Xiaheyan Village, Tupo Formation, Ningxia, China). A-C, Specimen CNU-NX1-143, holotype; A, drawing and photograph (negative imprint); B, detail of head and fore leg, as located on A (negative imprint); C, detail of forewing arculus (*), as located on A (negative imprint, light-mirrored); D, E, Specimen CNU-NX1-144; D, drawing (RHW omitted) and photograph (positive imprint); E, detail of hind wing arculus (*), as located on D (positive imprint).

Figure 2

Gulou carpenteri gen. et sp. nov. (Pennsylvanian; Xiaheyan Village, Tupo Formation, Ningxia, China). A, Specimen CNU-NX1-141, drawing and photograph (negative imprint); B-F, Specimen CNU-NX1-145; B, drawing and photograph (imprint polarity unknown); C, D, detail of hind leg tarsi, as located on B; E, detail of mid leg tarsus, as located on B (with tentative interpretation of segmentation); F, detail of fore leg, as located on B; G, Specimen CNU-NX1-140, drawing and photograph (negative imprint); H, Specimen CNU-NX1-146, drawing and photograph (negative imprint, light-mirrored).

Figure 3

Selection of extant stonefly forewings for comparison with fossil material. A-D, Acroneuria abnormis Newman, 1838; A, Specimen IWC OB 799 (♀), left forewing; B-C, Specimen IWC OB 800 (♀); B, Left forewing; C, Right forewing; D, Specimen IWC OB 810 (♂), right forewing; E-H, Acroneuria carolinensis Banks, 1905 (large arrows indicate various conditions of the connection between MP and CuA); E, Specimen IWC OB 833 (♀), left forewing; F-G, Specimen IWC OB 834 (♀); B, Left forewing; C, Right forewing; H, Specimen IWC OB 838 (♂), left forewing; I-L, Pteronarcys californica Newport, 1851 (large arrows indicate various conditions of the connection between RP and MA); I-J, Specimen IWC OB 816 (♀); I, Left forewing; J, Right forewing; K-L, Specimen IWC OB 824 (♂); K, Left forewing; L, Right forewing; M-P, Pteronarcys princeps Banks, 1907; M-N, Specimen IWC OB 828; M, Left forewing; N, Right forewing; O-P, Specimen IWC OB 830 (♂); O, Left forewing; P, Right forewing. RP and MP branches indicated by blue and red dots, respectively; r-m fold indicated by a dashed line.

Figure 4

Recent phylogenetic hypotheses on the position of Plecoptera with respect to fossil taxa (tentative 'cladistic-inspired' representations). A, According to various authors [2]; B, According to D. S. Aristov and A. P. Rasnitsyn [25].