Zygoptera, Selys, 1854

Nel, André, Poschmann, Markus J. & Wedmann, Sonja, 2020, New dragonflies and damselflies (Odonata) from the late Oligocene of Enspel (Rhineland-Palatinate, SW Germany), Palaeontologia Electronica (a 59) 23 (3), pp. 1-24 : 16-18

Undetermined Zygoptera (Wedmann, 2000: 15, pl. 9, fig. 1)

Figure 11

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Type material. Holotype PE 1995 /9164- LS (compression fossil of a rather well-preserved body with the three basal abdominal segments and bases of the four wings), stored at the State Collection of Natural History of Rhineland-Palatinate.

Diagnosis. Wing with a narrow area between CuA and posterior wing margin with two rows of cells.

Etymology. Named after the mined and now disappeared Stöffel hill, that once covered the sediments of paleolake Enspel.

Description. Head visible from frontal, hammer-shaped, with globular eyes well-separated, 4.6 mm wide, dark; meso-metathorax 9.3 mm long, 4.7 mm high, dorsally green-blue metallic; abdomen dorsally green-blue metallic, ventrally dark; second segment with secondary male genital apparatus; only parts of the wings between their bases and nodi preserved, 19.1 mm long, petiole of wings 4.8 mm long; distance from base to arculus 5.8 mm, from arculus to nodus 4.8 mm; estimated distance between nodus and wing apex 21.3 mm; estimated wing length 32.0 mm; wing 4.9 mm wide at level of nodus; Ax1 and Ax2 2.1 mm apart; Ax2 aligned with arculus; discoidal cells of fore- and hind wings identical, basal side 0.5 mm long, costal side 0.9 mm long, distal side (MAb) 0.9 mm long, ventral side 13.8 mm long; ScP kinked at nodus; nodal crossing and subnodus perpendicular to RA and RP1/2, respectively; bases of RP3/4 and IR2 mid-

PALAEO- ELECTRONICA.ORG way between nodus and arculus, that of RP3/4 3.0 mm distal of arculus, that of IR2 1.5 mm of that of RP3/4; one row of cells between RP3/4 and MAa and in postdiscoidal area in preserved parts; CuA strongly curved, ending on posterior wing margin well distal of level of nodus; two rows of cells between CuA and posterior wing margin.

Remarks. The wing venation of this fossil, although incompletely preserved, is very similar to that of the Oligocene genus Oligolestes in the shape of the discoidal cells, subnodus being perpendicular to RP1/2 and RA, bases of IR2 and RP3/4 located midway between arculus and nodus, arculus opposite Ax2, curved CuA with three rows of cells between it and posterior wing margin, base of RP2 well distal to subnodus, narrow area between RP3/4 and MAa (Schmidt, 1958: fig. 2). Statz (1935: 12) indicated that the arculus of O. grandis is 5.5 mm from the wing base but, after the photograph of Schmidt (1958: 3, pl. 1, fig. 1), the wing is broken at base, and thus the petiole is certainly longer than the estimation of Statz. Schmidt added that the wing is 39.0 mm long, and proposed a reconstruction with an elongate petiole figured with dotted lines. The ratio (wing width at level of nodus/distance nodus to arculus) is 1.05 for the two fossils, suggesting that the other main proportions are also similar. We calculate the estimated distance between the nodus and the wing apex of Oligolestes stoeffelensis sp. nov. after its ratio with the distance between arculus and nodus compared to that of O. grandis ; and thus we could establish an estimation of the total wing length of O. stoeffelensis sp. nov., which would be ca. 32 mm, thus it is distinctly smaller than O. grandis . The ratio (distance nodus to arculus/width cubital area) is 3.3 for O. grandis while it is 4.3 in O. stoeffelensis sp. nov., corresponding to a narrower cubital area in the latter.

The exact phylogenetic position of the genus Oligolestes remains somewhat enigmatic, although Nel et al. (2005a) considered it as belonging to the stem group of the Cenozoic family Sieblosiidae . The Sieblosiidae sensu stricto are characterized by the presence of a highly specialised nodus apparently traversed by ScP, as the terminal kink of CP is shifted basally together with the nodal and subnodal veinlets and the nodal membrane sclerotisation is reduced. Such structure is only present, among the Odonata , in the Mesozoic anisopteran family Aeschnidiidae . Our fossil, O. grandis , and Italolestes Nel et al., 2005 , have a ScP making a kink in the nodus as in the other Odonata . Italolestes differs from our fossil and O. grandis in the nodal crossing and subnodus of ‘normal’ obliquity (Nel et al., 2005a-b; Nel and Fleck, 2012). The Miocene sieblosiid genera Paraoligolestes Nel and Escuillié, 1993 and Miostenolestes Nel et al., 2005 have a venation also very similar to that of our fossil and O. grandis , especially in the rather narrow discoidal cells (compared to those of the Oligocene Sieblosia Handlirsch, 1906 , Stenolestes Scudder, 1895 , Parastenolestes Nel and Paicheler, 1994b , or the Miocene Germanolestes Nel and Fleck, 2012), but their ScP cross through the nodus (Nel and Escuillié, 1993; Nel and Paicheler, 1994b).

Notice that the current phylogenetic relationships of the Sieblosiidae remain uncertain, being either related to the Epiproctophora (the so-called ‘Anisozygoptera’ + Anisoptera) or to the Zygoptera (see discussion in Fleck et al., 2004).

Oligolestes stoeffelensis sp. nov. is of great interest for the head morphology in Sieblosiidae . In the few sieblosiid specimens with the head preserved, it is deformed due to the projection of the mouthparts and the crushing of the frons (Nel et al., 2005: fig. 11). This phenomenom is quite frequent among the fossil Zygoptera (Nel and Papazian, 1985: figs. 1-4; but see also http://mediaphoto.mnhn.fr/media/15184399435421FO8gTE- JGLR9en8s or http://mediaphoto.mnhn.fr/media/ 15184399443786A3TS35X0Rz2fEVq) or even in the Tarsophlebiidae (sister-group of Odonata ) (Fleck et al., 2014: fig. 1). In the case of Oligolestes stoeffelensis sp. nov., the lateral position of the body together with the rotation of the head have led to the absence of frontal projection of the mouthparts and to a minimal deformation of the head. It clearly confirms that the head of the Sieblosiidae is of zygopteran hammer-type.

Oligolestes stoeffelensis sp. nov. is also of great interest because it has the dorsal surface of the thorax and abdomen green-blue metallic (probably physical colors, as it can be frequently observed in fossil insects preserved in diatomites), a character that was unknown for the other Sieblosiidae . Preservation of metallic structural colors in Enspel insects was hitherto primarily known from exceptionally well-preserved beetle fossils (e.g., Wedmann, 2000, Wedmann et al., 2010, McNamara, 2013; Penney and Jepson, 2014: figs 46–48).

Figures

FIGURE 11. Oligolestes stoeffelensis sp. nov., holotype PE 1995/9164-LS. 1, Photograph of habitus; 2, Hind wing, Arc arculus, d discoidal cell, N nodus, Sn subnodus. Scale bar is 10 mm.