Pseudostenolestes bechlyi, Garrouste, Romain & Nel, André, 2015

Garrouste, Romain & Nel, André, 2015, New Eocene damselflies and first Cenozoic damsel-dragonfly of the isophlebiopteran lineage (Insecta: Odonata), Zootaxa 4028 (3), pp. 354-366 : 361-364

Pseudostenolestes bechlyi sp. nov.

( Figs. 8–13 )

Material. Holotype specimen MeI 14781a–b, paratypes specimens MeI 13209, MeI 14712, and MeI 14794a–b, all at SMF.

Etymology. Named after our friend and colleague Günter Bechly, for his contributions in odonatology.

Age and outcrop. Lower Middle Eocene, Geiseltalian (Lower Lutetian), ca. 47 million year old former Maar lake Messel, near Darmstadt, Hesse, Germany.

Diagnosis. As for the family, plus presence of a dark metallic zone crossing the wing around nodus level.

Descriptions. Specimen MeI 14781a–b: MeI 14781a (a hind wing base up to nodus level): length of fragment 26.8 mm, max. width 8.9 mm; MeI 14781b (apical two-thirds of wing): 25.7 mm long; max. width 8.2 mm; wing hyaline except for a broad dark area crossing it around nodus; wing ca. 32.3 mm long, 8.9 mm wide at nodus level; a very short petiole, 0.7 mm long; anal area with two rows of cells between AA and AP because of the presence of a strong vein emerging from posterior side of subdiscoidal cell in its middle and directed towards wing base; subdiscoidal cell broad and elongate, 1.2 mm long, 0.6 mm wide; CuP vein obliquely oriented between AA and MP+CuA; distance from base to arculus 2.9 mm, from arculus to nodus 8.6 mm, from nodus to pterostigma 12.3 mm; nodus in a basal position; pterostigma long and broad, 5.2 mm long, 0.8 mm wide, covering ca. four cells; pterostigmal brace absent; distance from wing base to Ax1 2.8 mm, from Ax1 to Ax2 1.8 mm, Ax1 aligned with arculus; at least three supplementary antenodal crossveins of first row between C and ScP distal of Ax2, without corresponding crossvein of second row; discoidal cell unicellular, 1.6 mm long, 1.2 mm wide, distinctly broadened in its distal part, basal side 0.6 mm long, anterior side 1.2 mm long, posterior side 1.1 mm long, distal side MAb 1.2 mm long; ScP not crossing through nodus, unlike in Stenolestes Scudder, 1895; nodal crossvein oblique; subnodus slightly oblique with corresponding crossvein below (between RP 1/2 and IR2) of inverted obliquity; ca. 17 postnodal crossveins preserved, not aligned with the 18 postsubnodal crossveins; bases of RP 3/4 and IR2 between arculus and nodus, closer to arculus than to nodus; base of RP 3/4 3.6 mm from arculus; base of RP 2 aligned with subnodus; base of IR1 five cells and 3.3 mm distally; oblique crossvein ‘O’ present two cells distal of base of RP 2; cubito-anal area with four-six rows of cells between CuA and posterior wing margin; CuA reaching posterior wing margin just distal of nodus level; CuA strongly curved; area between MP and posterior wing margin very broad; postdiscoidal area distally widened, with one or two secondary longitudinal veins between MP and MA; area between RP 3/4 and MA with two secondary longitudinal veins in between; four rows of cells between RP 3/4 and IR2 and two rows between RP 1 and IR1; three rows of cells between IR1 and RP 2 opposite pterostigma, but only one basally.

Specimen MeI 13209 (a nearly complete hind wing). Hyaline except for a metallic colored area crossing it around nodus; 34.3 mm long, 9.4 mm wide at nodus level; length of metallic colored area at costal margin 6.9 mm; nearly all preserved details of venation identical to those of specimen MeI 14781a–b.

Specimen MeI 14712 (distal two-thirds of a wing). Hyaline except for a metallic colored area around nodus. Preserved part 24.0 mm long; length of metallic colored area at costal margin 6.9 mm; all preserved parts are identical to those of specimen MeI 14781a–b.

Specimen MeI 14794a–b: fragment MeI 14794a (nearly complete wing) 34.3 mm long, 9.3 mm wide; MeI 14794b (fragment of median part of wing): max. width 9.2 mm. All preserved parts and pattern of coloration are identical to those of specimen MeI 14781a–b, except for the distinctly less oblique subnodus.

Discussion. The comparable preserved parts of these wings are nearly identical, supporting their attribution to the same taxon. The presence of discoidal cells of ‘sieblosiid type’ together with the positions of the bases of RP 3/ 4 and IR2 midway between arculus and nodus suggest possible affinities with the Sieblosiidae or with the Dysagrioninae: Petrolestini. The presence of the oblique vein ‘O’ together supports affinities with the Sieblosiidae rather than with the Dysagrioninae. Nevertheless, Pseudostenolestes strongly differs from the known Sieblosiidae in the following characters: shape of nodus with ScP not crossing through it; base of RP 2 only one or two cells distal of subnodus instead of being more than five cells distal of it; presence of secondary antenodal crossveins distal of Ax2. Furthermore Pseudostenolestes differs from both the Sieblosiidae and the Dysagrioninae (but also from all Zygoptera) in the very particular organization of the cubito-anal veins, viz. there is a strong vein emerging from posterior side of subdiscoidal cell in its middle and directed towards wing base. This structure constitutes one of the main synapomorphies of the Epiproctophora ( Fleck et al., 2003; Bechly, 2014). It corresponds to the vein CuAb that is separating from CuAa in the postero-distal angle of the subdiscoidal cell, and is distally meeting with AA to vanish in the basal part of cubito-anal area. This structure is clearly visible in the Heterophlebioptera Bechly, 1996, in the Epiophlebiidae , (less distinct in the Stenophlebiidae ), the Isophlebioptera, but also in the anisopteran Liassogomphidae (see Fleck et al. 2003). Fleck et al. (2004) proposed that the Sieblosiidae should be removed from the Zygoptera and could be the sister group of the Epiproctophora. Pseudostenolestes shares with the Epiproctophora the synapomorphic presence of a strong CuAb directed towards wing base.

Pseudostenolestes has a subdiscoidal cell broader than in the Zygoptera and the Sieblosiidae . This character is reminiscent of the situation in the Isophlebioptera in which the hind wing subdiscoidal cell is enlarged and has a bulged posterior margin (Nel et al., 1993; Bechly, 1996, 2014). Nevertheless, nearly all the representatives of this clade have subdiscoidal cells broader than in Pseudostenolestes and a different pattern of the longitudinal veins. Only the Cyclothemistidae, Bechly, 1996 (e.g., Cyclothemistinae Cyclothemis Pritykina, 1980, and Shurabiola Pritykina, 1980, and Pseudotriassothemistinae Pseudotriassothemis), have a subdiscoidal cell as narrow as Pseudostenolestes . Interestingly the Cyclothemistidae also share with Pseudostenolestes several other characters, viz. the distal side (MAb) of the discoidal cell is about twice as long as the basal side (= posterior part of arculus); the typical pattern of the longitudinal veins in Isophlebioptera is reversed (the same situation also occurs in the Cyclothemistidae Handlirsch, 1939); thus the postdiscoidal space is not narrowed and RP 3/4 is not parallel to IR2. If the Cyclothemistinae have a narrower cubito-anal area than that of Pseudostenolestes , the Triassic Pseudotriassothemis shares with Pseudostenolestes a broad cubito-anal area. Furthermore the CuP vein of Pseudostenolestes is obliquely oriented between AA and MP+CuA. This tendency is achieved in Pseudotriassothemis, in which CuP appears aligned with basal part of AA ( Fujiyama 1991). Pseudostenolestes differs from the Cyclothemistidae in the subnodus aligned with the nodal crossing, instead of being in a more distal position ( Pritykina 1980; Fujiyama 1991). This important difference is sufficient to justify a family separation.

Mesozoic representatives of the Isophlebioptera have the discoidal cells of the fore and hind wings of different shapes (see Nel et al. 1993). Thus we can suppose that the specimens MeI 14781a–b and MeI 13209 correspond to hind wings with closed discoidal cells.

Pseudostenolestes can be considered as the first Cenozoic and youngest Isophlebioptera, while this clade was previously known only between the Upper Triassic and the Lower Cretaceous. This implies a position of ‘ghost’ taxa of the Pseudostenolestidae during the Upper Cretaceous. Until now, if we except the Cenozoic Sieblosiidae , the Epiophlebioptera was the unique Mesozoic subclade (except the Anisoptera) of the Epiproctophora that survived the Cretaceous-Cenozoic mass extinction, as it is known by modern species and a very recently discovered taxon in the mid Cretaceous Burmese amber ( Bechly and Poinar 2013). The present discovery of an Isophlebioptera in the Paleogene demonstrates that this clade survived the major odonatological turnover of the Cenomanian-Turonian ( Nel et al. 2010) and the K-T extinction.

Figures

FIGURE 8. Pseudostenolestes bechlyi gen. et sp. nov., holotype MeI 14781 b, photograph of habitus. Scale bar represents 5.0 mm.

FIGURE 9. Pseudostenolestes bechlyi gen. et sp. nov., holotype MeI 14781 a, photograph of habitus. Scale bar represents 5.0 mm.

FIGURE 10. Pseudostenolestes bechlyi gen. et sp. nov., holotype MeI 14781 b, drawing of habitus. Scale bar represents 5.0 mm.

FIGURE 11. Pseudostenolestes bechlyi gen. et sp. nov., paratype MeI 13209, photograph of habitus. Scale bar represents 5.0 mm.

FIGURE 12. Pseudostenolestes bechlyi gen. et sp. nov., paratype MeI 14712, photograph of habitus. Scale bar represents 5.0 mm.

FIGURE 13. Pseudostenolestes bechlyi gen. et sp. nov., paratype MeI 14794 a, photograph of habitus. Scale bar represents 5.0 mm.